mercury/doc/user_guide.texi

\input texinfo
@setfilename mercury_user_guide.info
@settitle The Mercury User's Guide

@c --- texi2html doesn't support the @dir commands yet
@c @dircategory The Mercury Programming Language
@c @direntry
@c * Mercury User's Guide: (mercury_user_guide).  The Mercury User's Guide.
@c @end direntry

@c Uncomment the line below to enable documentation of the Aditi interface.
@set aditi

@c @smallbook
@c @cropmarks
@finalout
@setchapternewpage off

@c ----------------------------------------------------------------------------

@c We use the following indices in this document:
@c
@c	The "@cindex" / "cp" (concept) index:
@c		for general concepts (e.g. "Determinism", "Debugging", etc.)
@c	The "@pindex" / "pg" (program) index:
@c		for programs or shell scripts (mmc, mgnuc, etc.).
@c	The "@findex" / "fn" (function) index:
@c		for command-line options.
@c	The "@kindex" / "ky" (keystroke) index:
@c		for mdb commands.
@c	The "@vindex" / "vr" (variable) index:
@c		for environment variables and Mmake variables.
@c
@c That is in case we ever want to produce separate indices for the
@c different categories.  Currently, however, we merge them all into
@c a single index, via the commands below.

@syncodeindex fn cp
@syncodeindex ky cp
@syncodeindex vr cp
@syncodeindex pg cp

@c ----------------------------------------------------------------------------

@ifinfo
This file documents the Mercury implementation, version <VERSION>.

Copyright (C) 1995-2002 The University of Melbourne.

Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.

@ignore
Permission is granted to process this file through Tex and print the
results, provided the printed document carries copying permission
notice identical to this one except for the removal of this paragraph
(this paragraph not being relevant to the printed manual).

@end ignore
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided also that
the entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions.
@end ifinfo

@titlepage
@title The Mercury User's Guide
@subtitle Version <VERSION>
@author Fergus Henderson
@author Thomas Conway
@author Zoltan Somogyi
@author Peter Ross
@author Tyson Dowd
@page
@vskip 0pt plus 1filll
Copyright @copyright{} 1995-2002 The University of Melbourne.

Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided also that
the entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions.
@end titlepage

@c ----------------------------------------------------------------------------

@contents
@page

@c ----------------------------------------------------------------------------

@ifinfo
@node Top,,, (mercury)
@top The Mercury User's Guide, version <VERSION>

This guide describes the compilation environment of Mercury ---
how to build and debug Mercury programs.

@menu
* Introduction::    General overview.
* Filenames::       File naming conventions.
* Using mmc::       Compiling and linking programs with the Mercury compiler.
* Running::         Execution of programs built with the Mercury compiler.
* Using Mmake::     ``Mercury Make'', a tool for building Mercury programs.
* Libraries::       Creating and using libraries of Mercury modules.
* Using Aditi::     Executing Mercury predicates using the Aditi
                    deductive database.
* Debugging::       The Mercury debugger @samp{mdb}.
* Profiling::       Analyzing the performance of Mercury programs.
* Invocation::      List of options for the Mercury compiler.
* Environment::     Environment variables used by the compiler and utilities.
* C compilers::     How to use a C compiler other than GNU C.
* Foreign language interface:: Interfacing to other programming
		    languages from Mercury.
* Index::
@end menu
@end ifinfo

@c ----------------------------------------------------------------------------

@node Introduction
@chapter Introduction

This document describes the compilation environment of Mercury.
It describes how to use @samp{mmc}, the Mercury compiler;
how to use @samp{mmake}, the ``Mercury make'' program,
a tool built on top of ordinary or GNU make
to simplify the handling of Mercury programs;
how to use @samp{mdb}, the Mercury debugger;
and how to use @samp{mprof}, the Mercury profiler.

We strongly recommend that programmers use @samp{mmake} rather
than invoking @samp{mmc} directly, because @samp{mmake} is generally
easier to use and avoids unnecessary recompilation.

@c ----------------------------------------------------------------------------

@node Filenames
@chapter File naming conventions
@cindex File extensions
@cindex File names

Mercury source files must be named @file{*.m}.
Each Mercury source file should contain a single Mercury module
whose module name should be the same as the filename without
the @samp{.m} extension.

The Mercury implementation uses a variety of intermediate files, which
are described below.  But all you really need to know is how to name
source files.  For historical reasons, the default behaviour is for
intermediate files to be created in the current directory, but if you
use the @samp{--use-subdirs} option to @samp{mmc} or @samp{mmake}, all
@findex --use-subdirs
these intermediate files will be created in a @file{Mercury}
subdirectory, where you can happily ignore them.
Thus you may wish to skip the rest of this chapter.

In cases where the source file name and module name don't match,
the names for intermediate files are based on the name of the
module from which they are derived, not on the source file name.

Files ending in @file{.int}, @file{.int0}, @file{.int2} and @file{.int3}
are interface files; these are generated automatically by the compiler,
using the @samp{--make-interface} (or @samp{--make-int}),
@samp{--make-private-interface} (or @samp{--make-priv-int}),
@samp{--make-short-interface} (or @samp{--make-short-int}) options.
@findex --make-int
@findex --make-interface
@findex --make-short-int
@findex --make-short-interface
@findex --make-priv-interface
@findex --make-private-interface
@findex --make-optimization-interface
@findex --make-transitive-optimization-interface
@findex --make-trans-opt-int
Files ending in @file{.opt} are
interface files used in inter-module optimization,
and are created using the @samp{--make-optimization-interface}
(or @samp{--make-opt-int}) option.
Similarly, files ending in @file{.trans_opt} are interface files used in
transitive inter-module optimization, and are created using the
@samp{--make-transitive-optimization-interface}
(or @samp{--make-trans-opt-int}) option.

Since the interface of a module changes less often than its implementation,
the @file{.int}, @file{.int0}, @file{.int2}, @file{.int3}, @file{.opt},
and @file{.trans_opt} files will remain unchanged on many compilations.
To avoid unnecessary recompilations of the clients of the module,
the timestamps on the these files are updated only if their contents change.
@file{.date}, @file{.date0}, @file{.date3}, @file{.optdate},
and @file{.trans_opt_date}
files associated with the module are used as date stamps;
they are used when deciding whether the interface files need to be regenerated.

@file{.c_date}, @file{.il_date}, @file{.java_date},
@file{.s_date} and @file{.pic_s_date} files
perform a similar function for @file{.c}, @file{.il}, @file{.java},
@file{.s} and @file{.pic_s} files respectively. When smart recompilation
(@pxref{Auxiliary output options}) works out that a module
does not need to be recompiled, the timestamp file for the
target file is updated, and the timestamp of the target file
is left unchanged.
@findex --smart-recompilation

@file{.used} files contain dependency information for smart recompilation
(@pxref{Auxiliary output options}).
@findex --smart-recompilation

Files ending in @file{.d} are automatically-generated Makefile fragments
which contain the dependencies for a module.
Files ending in @file{.dep} are automatically-generated Makefile fragments
which contain the rules for an entire program.
Files ending in @file{.dv} are automatically-generated Makefile fragments
which contain variable definitions for an entire program.

As usual, @file{.c} files are C source code,
@file{.h} files are C header files,
and @file{.o} files are object code.
In addition, @file{.pic_o} files are object code files
that contain position-independent code (PIC).
@file{.s} files and @file{.pic_s} files are assembly language.
@file{.java} and @file{.class} files are Java source code
and Java bytecode respectively.
@file{.il} files are Microsoft Intermediate Language (MSIL) files
for the .NET Common Language Runtime.
@c XXX mention .dll and .exe?

@ifset aditi
Files ending in @file{.rlo} are Aditi-RL bytecode files, which are
executed by the Aditi deductive database system (@pxref{Using Aditi}).
@end ifset

@c ----------------------------------------------------------------------------

@node Using mmc
@chapter Using the Mercury compiler

Following a long Unix tradition,
the Mercury compiler is called @samp{mmc}
(for ``Melbourne Mercury Compiler'').
@pindex mmc
Some of its options (e.g. @samp{-c}, @samp{-o}, and @samp{-I})
have a similar meaning to that in other Unix compilers.

Arguments to @samp{mmc} may be either file names (ending in @samp{.m}),
or module names, with @samp{.} (rather than @samp{__} or @samp{:})
as the module qualifier.  For a module name such as @samp{foo.bar.baz},
the compiler will look for the source in files @file{foo.bar.baz.m},
@file{bar.baz.m}, and @file{baz.m}, in that order.
Note that if the file name does not include all the module
qualifiers (e.g. if it is @file{bar.baz.m} or @file{baz.m}
rather than @file{foo.bar.baz.m}), then the module name in the
@samp{:- module} declaration for that module must be fully qualified.
To make the compiler look in another file for a module, use
@samp{mmc -f @var{sources-files}} to generate a mapping from module name
to file name, where @var{sources-files} is the list of source files in
the directory (@pxref{Output options}).

To compile a program which consists of just a single source file,
use the command

@example
mmc @var{filename}.m
@end example

Unlike traditional Unix compilers, however,
@samp{mmc} will put the executable into a file called @file{@var{filename}},
not @file{a.out}.

For programs that consist of more than one source file, we @emph{strongly}
recommend that you use Mmake (@pxref{Using Mmake}).  Mmake will perform
all the steps listed below, using automatic dependency analysis
to ensure that things are done in the right order, and that
steps are not repeated unnecessarily.
If you use Mmake, then you don't need to understand the details
of how the Mercury implementation goes about building programs.
Thus you may wish to skip the rest of this chapter.

To compile a source file to object code without creating an executable,
use the command

@example
mmc -c @var{filename}.m
@end example

@samp{mmc} will put the object code into a file called @file{@var{module}.o},
where @var{module} is the name of the Mercury module defined in
@file{@var{filename}.m}.
It also will leave the intermediate C code in a file called
@file{@var{module}.c}.
If the source file contains nested modules, then each sub-module will get
compiled to separate C and object files.

Before you can compile a module,
you must make the interface files
for the modules that it imports (directly or indirectly).
You can create the interface files for one or more source files
using the following commands:

@example
mmc --make-short-int @var{filename1}.m @var{filename2}.m ...
mmc --make-priv-int @var{filename1}.m @var{filename2}.m ...
mmc --make-int @var{filename1}.m @var{filename2}.m ...
@end example
@findex --make-short-int
@findex --make-priv-int
@findex --make-int

If you are going to compile with @samp{--intermodule-optimization} enabled,
then you also need to create the optimization interface files.

@example
mmc --make-opt-int @var{filename1}.m @var{filename2}.m ...
@end example
@findex --make-opt-int

If you are going to compile with @samp{--transitive-intermodule-optimization}
enabled, then you also need to create the transitive optimization files.
@findex --transitive-intermodule-optimization

@example
mmc --make-trans-opt @var{filename1}.m @var{filename2}.m ...
@end example
@findex --make-trans-opt

Given that you have made all the interface files,
one way to create an executable for a multi-module program
is to compile all the modules at the same time
using the command

@example
mmc @var{filename1}.m @var{filename2}.m ...
@end example

This will by default put the resulting executable in @file{@var{filename1}},
but you can use the @samp{-o @var{filename}} option to specify a different
name for the output file, if you so desire.
@findex -o

The other way to create an executable for a multi-module program
is to compile each module separately using @samp{mmc -c},
@findex -c
and then link the resulting object files together.
The linking is a two stage process.

First, you must create and compile an @emph{initialization file},
which is a C source file
containing calls to automatically generated initialization functions
contained in the C code of the modules of the program:

@example
c2init @var{module1}.c @var{module2}.c ... > @var{main-module}_init.c,
mgnuc -c @var{main-module}_init.c
@end example
@pindex c2init
@pindex mgnuc

The @samp{c2init} command line must contain
the name of the C file of every module in the program.
The order of the arguments is not important.
The @samp{mgnuc} command is the Mercury GNU C compiler;
it is a shell script that invokes the GNU C compiler @samp{gcc}
@c (or some other C compiler if GNU C is not available)
with the options appropriate for compiling
the C programs generated by Mercury.

You then link the object code of each module
with the object code of the initialization file to yield the executable:

@example
ml -o @var{main-module} @var{module1}.o @var{module2}.o ... @var{main_module}_init.o
@end example
@pindex ml

@samp{ml}, the Mercury linker, is another shell script
that invokes a C compiler with options appropriate for Mercury,
this time for linking.  @samp{ml} also pipes any error messages
from the linker through @samp{mdemangle}, the Mercury symbol demangler,
so that error messages refer to predicate and function names from
the Mercury source code rather than to the names used in the intermediate
C code.

The above command puts the executable in the file @file{@var{main-module}}.
The same command line without the @samp{-o} option
would put the executable into the file @file{a.out}.

@samp{mmc} and @samp{ml} both accept a @samp{-v} (verbose) option.
You can use that option to see what is actually going on.
For the full set of options of @samp{mmc}, see @ref{Invocation}.

@c ----------------------------------------------------------------------------

@node Running
@chapter Running programs

Once you have created an executable for a Mercury program,
you can go ahead and execute it.  You may however wish to specify
certain options to the Mercury runtime system.
The Mercury runtime accepts
options via the @samp{MERCURY_OPTIONS} environment variable.
@vindex MERCURY_OPTIONS
The most useful of these are the options that set the size of the stacks.
(For the full list of available options, see @ref{Environment}.)

@c XXX FIXME This is wrong for the case when --high-level-code is enabled.
The det stack and the nondet stack
are allocated fixed sizes at program start-up.
The default size is 4096k for the det stack and 128k for the nondet stack,
but these can be overridden with the
@samp{--detstack-size} and @samp{--nondetstack-size} options,
@findex --detstack-size
@findex --nondetstack-size
whose arguments are the desired sizes of the det and nondet stacks
respectively, in units of kilobytes.
On operating systems that provide the appropriate support,
the Mercury runtime will ensure that stack overflow
is trapped by the virtual memory system.
@cindex Stack size
@cindex Stack overflow

With conservative garbage collection (the default),
the heap will start out with a zero size,
and will be dynamically expanded as needed,
When not using conservative garbage collection,
the heap has a fixed size like the stacks.
The default size is 4 Mb, but this can be overridden
with the @samp{--heap-size} option.
@cindex Heap size
@cindex Heap overflow

@c ----------------------------------------------------------------------------

@node Using Mmake
@chapter Using Mmake
@pindex mmake
@pindex make: see Mmake
@cindex Building programs
@cindex Recompiling

Mmake, short for ``Mercury Make'',
is a tool for building Mercury programs
that is built on top of ordinary or GNU Make @footnote{
We might eventually add support for ordinary ``Make'' programs,
but currently only GNU Make is supported.}.
With Mmake, building even a complicated Mercury program
consisting of a number of modules is as simple as

@example
mmc -f @var{source-files}
mmake @var{main-module}.depend
mmake @var{main-module}
@end example

Mmake only recompiles those files that need to be recompiled,
based on automatically generated dependency information.
Most of the dependencies are stored in @file{.d} files that are
automatically recomputed every time you recompile,
so they are never out-of-date.
A little bit of the dependency information is stored in @file{.dep}
and @file{.dv} files which are more expensive to recompute.
The @samp{mmake @var{main-module}.depend} command which recreates the
@file{@var{main-module}.dep} and @file{@var{main-module}.dv} files needs
to be repeated only when you add or remove a module from your program,
and there is no danger of getting an inconsistent executable if you forget
this step --- instead you will get a compile or link error.

The @samp{mmc -f} step above is only required if there are any source
files for which the file name does not match the module name.
@samp{mmc -f} generates a file @file{Mercury.modules} containing
a mapping from module name to source file.  The @file{Mercury.modules}
file must be updated when a source file for which the file name does
not match the module name is added to or removed from the directory.

@samp{mmake} allows you to build more than one program in the same directory.
Each program must have its own @file{.dep} and @file{.dv} files,
and therefore you must run @samp{mmake @var{program}.depend}
for each program.  The @samp{Mercury.modules} file is used for
all programs in the directory.

If there is a file called @samp{Mmake} or @samp{Mmakefile} in the
current directory,
Mmake will include that file in its automatically-generated Makefile.
The @samp{Mmake} file can override the default values of
various variables used by Mmake's builtin rules,
or it can add additional rules, dependencies, and actions.

Mmake's builtin rules are defined by the file
@file{@var{prefix}/lib/mercury/mmake/Mmake.rules}
(where @var{prefix} is @file{/usr/local/mercury-@var{version}} by default,
and @var{version} is the version number, e.g. @samp{0.6}),
as well as the rules and variables in the automatically-generated
@file{.dep} and @file{.dv} files.
These rules define the following targets:

@table @file
@item @var{main-module}.depend
Creates the files @file{@var{main-module}.dep} and
@file{@var{main-module}.dv} from @file{@var{main-module}.m}
and the modules it imports.
This step must be performed first.
It is also required whenever you wish to change the level of
inter-module optimization performed (@pxref{Overall optimization options}).

@item @var{main-module}.ints
Ensure that the interface files for @var{main-module}
and its imported modules are up-to-date.
(If the underlying @samp{make} program does not handle transitive dependencies,
this step may be necessary before
attempting to make @file{@var{main-module}} or @file{@var{main-module}.check};
if the underlying @samp{make} is GNU Make, this step should not be necessary.)

@item @var{main-module}.check
Perform semantic checking on @var{main-module} and its imported modules.
Error messages are placed in @file{.err} files.

@item @var{main-module}
Compiles and links @var{main-module} using the Mercury compiler.
Error messages are placed in @file{.err} files.

@item @var{main-module}.split
Compiles and links @var{main-module} using the Mercury compiler,
with the Mercury compiler's @samp{--split-c-files} option enabled.
For more information about @samp{--split-c-files}, see
@ref{Output-level (LLDS -> C) optimization options}.

@item @var{main-module}.javas
Compiles @var{main-module} to Java source files (@file{*.java}).

@item @var{main-module}.classes
Compiles @var{main-module} to Java bytecode files (@file{*.class}).

@item @var{main-module}.ils
Compiles @var{main-module} to MSIL files (@file{*.il})
for the .NET Common Language Runtime.

@c XXX mention .dlls and .exe targets?

@item lib@var{main-module}
Builds a library whose top-level module is @var{main-module}.
This will build a static object library, a shared object library
(for platforms that support it), and the necessary interface files.
For more information, see @ref{Libraries}.

@item lib@var{main-module}.install
Builds and installs a library whose top-level module is @var{main-module}.
This target will build and install a static object library and
(for platforms that support it) a shared object library,
for the default grade and also for the additional grades specified
in the @code{LIBGRADES} variable.  It will also build and install the
necessary interface files. The variable @code{INSTALL} specifies
the name of the command to use to install each file, by default
@samp{cp}. The variable @code{INSTALL_MKDIR} specifies the command to use
to create directories, by default @samp{mkdir -p}.
For more information, see @ref{Installing libraries}.
@vindex LIBGRADES
@vindex INSTALL
@vindex INSTALL_MKDIR

@item @var{main-module}.clean
Removes the automatically generated files
that contain the compiled code of the program
and the error messages produced by the compiler.
Specifically, this will remove all the @samp{.c}, @samp{.s}, @samp{.o},
@samp{.pic_o}, @samp{.prof}, @samp{.no}, @samp{.ql}, @samp{.used},
@ifset aditi
@samp{.schema},
@end ifset
and @samp{.err} files
belonging to the named @var{main-module} or its imported modules.
Use this target whenever you wish to change compilation model
(@pxref{Compilation model options}).
This target is also recommended whenever you wish to change the level
of inter-module optimization performed (@pxref{Overall optimization
options}) in addition to the mandatory @var{main-module}.depend.

@item @var{main-module}.realclean
Removes all the automatically generated files.
In addition to the files removed by @var{main-module}.clean, this
removes the @samp{.int}, @samp{.int0}, @samp{.int2},
@samp{.int3}, @samp{.opt}, @samp{.trans_opt},
@samp{.date}, @samp{.date0}, @samp{.date3}, @samp{.optdate},
@samp{.trans_opt_date},
@ifset aditi
@samp{.rlo},
@end ifset
@samp{.h} and @samp{.d} files
belonging to one of the modules of the program,
and also the various possible executables, libraries and dependency files
for the program as a whole ---
@samp{@var{main-module}},
@samp{@var{main-module}.split},
@samp{lib@var{main-module}.a},
@samp{lib@var{main-module}.so},
@samp{@var{main-module}.split.a},
@samp{@var{main-module}.init},
@samp{@var{main-module}.dep}
and
@samp{@var{main-module}.dv}.

@item clean
This makes @samp{@var{main-module}.clean} for every @var{main-module}
for which there is a @file{@var{main-module}.dep} file in the current
directory, as well as deleting the profiling files
@samp{Prof.CallPair},
@samp{Prof.Counts},
@samp{Prof.Decl},
@samp{Prof.MemWords}
and
@samp{Prof.MemCells}.

@item realclean
This makes @samp{@var{main-module}.realclean} for every @var{main-module}
for which there is a @file{@var{main-module}.dep} file in the current
directory, as well as deleting the profiling files as per the @samp{clean}
target.

@end table

@cindex Variables, Mmake
@cindex Mmake variables
The variables used by the builtin rules (and their default values) are
defined in the file @file{@var{prefix}/lib/mercury/mmake/Mmake.vars}, however
these may be overridden by user @samp{Mmake} files.  Some of the more
useful variables are:

@table @code

@item MAIN_TARGET
@vindex MAIN_TARGET
The name of the default target to create if @samp{mmake} is invoked with
any target explicitly named on the command line.

@item MC
@vindex MC
The executable that invokes the Mercury compiler.

@item GRADEFLAGS and EXTRA_GRADEFLAGS
@vindex GRADEFLAGS
@vindex EXTRA_GRADEFLAGS
Compilation model options (@pxref{Compilation model options})
to pass to the Mercury compiler, linker, and other tools
(in particular @code{mmc}, @code{mgnuc}, @code{ml}, and @code{c2init}).

@item MCFLAGS and EXTRA_MCFLAGS
@vindex MCFLAGS
@vindex EXTRA_MCFLAGS
Options to pass to the Mercury compiler.
(Note that compilation model options should be
specified in @code{GRADEFLAGS}, not in @code{MCFLAGS}.)

@item MGNUC
@vindex MGNUC
The executable that invokes the C compiler.

@item MGNUCFLAGS and EXTRA_MGNUCFLAGS
@vindex MGNUCFLAGS
@vindex EXTRA_MGNUCFLAGS
Options to pass to the mgnuc script.

@item CFLAGS and EXTRA_CFLAGS
@vindex CFLAGS
@vindex EXTRA_CFLAGS
Options to pass to the C compiler.

@item JAVACLAGS and EXTRA_JAVACFLAGS
@vindex JAVACFLAGS
@vindex EXTRA_JAVACFLAGS
Options to pass to the Java compiler (if you are using it).

@item MS_CLFLAGS and EXTRA_MS_CLFLAGS
@vindex MS_CLFLAGS
@vindex EXTRA_MS_CLFLAGS
Options to pass to the Microsoft command line C++ compiler (if you are
using it).

@item MS_CL_NOASM 
@vindex MS_CL_NOASM
The option to control whether the Microsoft command line C++ compiler
will generate .NET assemblies from Managed C++ files.  Set to
@samp{:noAssembly} to turn off assembly generation, leave empty to turn
on assembly generation.  The default is to leave this variable empty.

@item ML
@vindex ML
The executable that invokes the linker.

@item MLFLAGS and EXTRA_MLFLAGS
@vindex MLFLAGS
@vindex EXTRA_MLFLAGS
Options to pass to the ml and c2init scripts.
(Note that compilation model options should be
specified in @code{GRADEFLAGS}, not in @code{MLFLAGS}.)

@item LDFLAGS and EXTRA_LDFLAGS
@vindex LDFLAGS
@vindex EXTRA_LDFLAGS
Options to pass to the command used by the ml script to link
executables (use @code{ml --print-link-command} to find out
what command is used, usually the C compiler).

@item LD_LIBFLAGS and EXTRA_LD_LIBFLAGS
@vindex LD_LIBFLAGS
@vindex EXTRA_LD_LIBFLAGS
Options to pass to the command used to by the ml script to link
shared libraries (use @code{ml --print-shared-lib-link-command}
to find out what command is used, usually the C compiler
or the system linker, depending on the platform).

@item MLLIBS and EXTRA_MLLIBS
@vindex MLLIBS
@vindex EXTRA_MLLIBS
A list of @samp{-l} options specifying libraries used by the program
(or library) that you are building.  @xref{Using libraries}.

@item MLOBJS and EXTRA_MLOBJS
@vindex MLOBJS
@vindex EXTRA_MLOBJS
A list of extra object files to link into the program (or library)
that you are building.

@item C2INITFLAGS and EXTRA_C2INITFLAGS
@vindex C2INITFLAGS
@vindex EXTRA_C2INITFLAGS
Options to pass to the linker and the c2init program.
@code{C2INITFLAGS} and @code{EXTRA_C2INITFLAGS} are obsolete synonyms
for @code{MLFLAGS} and @code{EXTRA_MLFLAGS} (@code{ml} and @code{c2init}
take the same set of options).
(Note that compilation model options and extra files to be processed by
c2init should not be specified in @code{C2INITFLAGS} - they should be
specified in @code{GRADEFLAGS} and @code{C2INITARGS}, respectively.)

@item C2INITARGS and EXTRA_C2INITARGS
@vindex C2INITARGS
@vindex EXTRA_C2INITARGS
Extra files to be processed by c2init.  These variables should not be
used for specifying flags to c2init (those should be specified in
@code{MLFLAGS}) since they are also used to derive extra dependency
information.

@item EXTRA_LIBRARIES
@vindex EXTRA_LIBRARIES
A list of extra Mercury libraries to link into any programs or libraries
that you are building.
Libraries should be specified using their base name; that is, without any
@samp{lib} prefix or extension.
For example the library including the files @file{libfoo.a} and
@file{foo.init} would be referred to as just @samp{foo}.
@xref{Using libraries}.

@item EXTRA_LIB_DIRS
@vindex EXTRA_LIB_DIRS
A list of extra Mercury library directory hierarchies to search when
looking for extra libraries.  @xref{Using libraries}.

@item INSTALL_PREFIX
@vindex INSTALL_PREFIX
The path to the root of the directory hierarchy where the libraries,
etc. you are building should be installed.  The default is to install in
the same location as the Mercury compiler being used to do the install.

@item INSTALL
@vindex INSTALL
The command used to install each file in a library. The command should
take a list of files to install and the location to install them.
The default command is @samp{cp}.

@item INSTALL_MKDIR
@vindex INSTALL_MKDIR
The command used to create each directory in the directory hierarchy
where the libraries are to be installed. The default command is
@samp{mkdir -p}.

@item LIBGRADES
@vindex LIBGRADES
A list of additional grades which should be built when installing libraries.
The default is to install the Mercury compiler's default set of grades.
Note that this may not be the set of grades in which the standard libraries
were actually installed.
@vindex GRADEFLAGS
Note also that any @code{GRADEFLAGS} settings will also be applied when
the library is built in each of the listed grades, so you may not get what
you expect if those options are not subsumed by each of the grades listed.
@end table

Other variables also exist - see
@file{@var{prefix}/lib/mercury/mmake/Mmake.vars} for a complete list.

If you wish to temporarily change the flags passed to an executable,
rather than setting the various @samp{FLAGS} variables directly, you can
set an @samp{EXTRA_} variable.  This is particularly intended for
use where a shell script needs to call mmake and add an extra parameter,
without interfering with the flag settings in the @samp{Mmakefile}.

For each of the variables for which there is version with an @samp{EXTRA_}
prefix, there is also a version with an @samp{ALL_} prefix that
is defined to include both the ordinary and the @samp{EXTRA_} version.
If you wish to @emph{use} the values any of these variables
in your Mmakefile (as opposed to @emph{setting} the values),
then you should use the @samp{ALL_} version.

It is also possible to override these variables on a per-file basis.
For example, if you have a module called say @file{bad_style.m}
which triggers lots of compiler warnings, and you want to disable
the warnings just for that file, but keep them for all the other modules,
then you can override @code{MCFLAGS} just for that file.  This is done by
setting the variable @samp{MCFLAGS-bad_style}, as shown here:

@example
MCFLAGS-bad_style = --inhibit-warnings
@end example

Mmake has a few options, including @samp{--use-subdirs},
@samp{--save-makefile}, @samp{--verbose}, and @samp{--no-warn-undefined-vars}.
For details about these options, see the man page or type @samp{mmake --help}.

Finally, since Mmake is built on top of Make or GNU Make, you can also
make use of the features and options supported by the underlying Make.
In particular, GNU Make has support for running jobs in parallel, which
is very useful if you have a machine with more than one CPU.

As an alternative to Mmake, the Mercury compiler now contains a
significant part of the functionality of Mmake, using the
@samp{--make} option.  
@findex --make
To use the compiler's internal make with Mmake, set the
@samp{MMAKE_USE_MMC_MAKE} environment variable to @samp{yes},
or create a file @file{Mercury.options} in the directory
containing the source files.  When this is done, Mmake will
process source files written in other programming languages,
but all Mercury compilation will be done by @samp{mmc --make}.

The advantages of the @samp{mmc --make} over Mmake are that there
is no @samp{mmake depend} step and the dependencies are more accurate.
Library installation (@pxref{Libraries}) and parallel makes are
not yet supported.

The Mmake variables above can be used by @samp{mmc --make} if they
are set in a file called @file{Mercury.options}. The @file{Mercury.options}
file has the same syntax as an Mmakefile, but only variable assignments and
@samp{include} directives are allowed.  All variables in the Mercury.options
are treated as if they are assigned using @samp{:=}.  As with Mmake,
variables may also be set in the environment.

@c ----------------------------------------------------------------------------

@node Libraries
@chapter Libraries
@cindex Libraries

Often you will want to use a particular set of Mercury modules
in more than one program.  The Mercury implementation
includes support for developing libraries, i.e. sets of Mercury modules
intended for reuse.  It allows separate compilation of libraries
and, on many platforms, it supports shared object libraries.

@menu
* Writing libraries::
* Building libraries::
* Installing libraries::
* Using libraries::
@end menu

@node Writing libraries
@section Writing libraries

A Mercury library is identified by a top-level module,
which should contain all of the modules in that library as sub-modules.
It may be as simple as this @file{mypackage.m} file:

@example
:- module mypackage.
:- interface.
:- include_module foo, bar, baz.
@end example

@noindent
This defines a module @samp{mypackage} containing
sub-modules @samp{mypackage:foo}, @samp{mypackage:bar},
and @samp{mypackage:baz}.

It is also possible to build libraries of unrelated
modules, so long as the top-level module imports all
the necessary modules.  For example:

@example
:- module blah.
:- import_module fee, fie, foe, fum.
@end example

@noindent
This example defines a module @samp{blah}, which has
no functionality of its own, and which is just used
for grouping the unrelated modules @samp{fee},
@samp{fie}, @samp{foe}, and @samp{fum}.

Generally it is better style for each library to consist
of a single module which encapsulates its sub-modules,
as in the first example, rather than just a group of
unrelated modules, as in the second example.

@node Building libraries
@section Building libraries
@cindex Shared objects
@cindex Shared libraries
@cindex Static libraries
@cindex Position independent code
@cindex PIC (position independent code)

Generally Mmake will do most of the work of building
libraries automatically.  Here's a sample @code{Mmakefile} for
creating a library.

@example
MAIN_TARGET = libmypackage
depend: mypackage.depend
@end example

The Mmake target @samp{lib@var{foo}} is a built-in target for
creating a library whose top-level module is @samp{@var{foo}.m}.
The automatically generated Mmake rules for the target @samp{lib@var{foo}}
will create all the files needed to use the library.
(You will need to run @samp{mmake @var{foo}.depend} first
to generate the module dependency information.)

Mmake will create static (non-shared) object libraries
and, on most platforms, shared object libraries;
however, we do not yet support the creation of dynamic link
libraries (DLLs) on Windows.
Static libraries are created using the standard tools @samp{ar}
and @samp{ranlib}.
Shared libraries are created using the @samp{--make-shared-lib}
option to @samp{ml}.
The automatically-generated Make rules for @samp{libmypackage}
will look something like this:

@example
libmypackage: libmypackage.a libmypackage.so \
		$(mypackage.ints) $(mypackage.int3s) \
		$(mypackage.opts) $(mypackage.trans_opts) mypackage.init

libmypackage.a: $(mypackage.os)
	rm -f libmypackage.a
	$(AR) $(ARFLAGS) libmypackage.a $(mypackage.os) $(MLOBJS)
	$(RANLIB) $(RANLIBFLAGS) mypackage.a

libmypackage.so: $(mypackage.pic_os)
	$(ML) $(MLFLAGS) --make-shared-lib -o libmypackage.so \
		$(mypackage.pic_os) $(MLPICOBJS) $(MLLIBS)

libmypackage.init:
	...

clean:
	rm -f libmypackage.a libmypackage.so
@end example
@vindex AR
@vindex ARFLAGS
@vindex MLOBJS
@vindex RANLIB
@vindex RANLIBFLAGS
@vindex ML
@vindex MLFLAGS
@vindex MLPICOBJS
@vindex MLLIBS

If necessary, you can override the default definitions of the variables
such as @samp{ML}, @samp{MLFLAGS}, @samp{MLPICOBJS}, and @samp{MLLIBS}
to customize the way shared libraries are built.  Similarly @samp{AR},
@samp{ARFLAGS}, @samp{MLOBJS}, @samp{RANLIB}, and @samp{RANLIBFLAGS}
control the way static libraries are built.  (The @samp{MLOBJS} variable
is supposed to contain a list of additional object files to link into
the library, while the @samp{MLLIBS} variable should contain a list of
@samp{-l} options naming other libraries used by this library.
@samp{MLPICOBJS} is described below.)

Note that to use a library, as well as the shared or static object library,
you also need the interface files.  That's why the
@samp{libmypackage} target builds @samp{$(mypackage.ints)} and
@samp{$(mypackage.int3s)}.
If the people using the library are going to use intermodule
optimization, you will also need the intermodule optimization interfaces.
The @samp{libmypackage} target will build @samp{$(mypackage.opts)} if
@samp{--intermodule-optimization} is specified in your @samp{MCFLAGS}
variable (this is recommended).
@findex --intermodule-optimization
Similarly, if the people using the library are going to use transitive
intermodule optimization, you will also need the transitive intermodule
optimization interfaces (@samp{$(mypackage.trans_opt)}).
These will be built if @samp{--trans-intermod-opt} is specified in your
@samp{MCFLAGS} variable.
@findex --trans-intermod-opt

In addition, with certain compilation grades, programs will need to
execute some startup code to initialize the library; the
@samp{mypackage.init} file contains information about initialization
code for the library.  The @samp{libmypackage} target will build this file.

On some platforms, shared objects must be created using position independent
code (PIC), which requires passing some special options to the C compiler.
On these platforms, @code{Mmake} will create @file{.pic_o} files,
and @samp{$(mypackage.pic_os)} will contain a list of the @file{.pic_o} files
for the library whose top-level module is @samp{mypackage}.
In addition, @samp{$(MLPICOBJS)} will be set to @samp{$MLOBJS} with
all occurrences of @samp{.o} replaced with @samp{.pic_o}.
On other platforms, position independent code is the default,
so @samp{$(mypackage.pic_os)} will just be the same as @samp{$(mypackage.os)},
which contains a list of the @file{.o} files for that module,
and @samp{$(MLPICOBJS)} will be the same as @samp{$(MLOBJS)}.

@node Installing libraries
@section Installing libraries

@samp{mmake} has support for alternative library directory hierarchies.
These have the same structure as the @file{@var{prefix}/lib/mercury} tree,
including the different subdirectories for different grades and different
machine architectures.

In order to support the installation of a library into such a tree, you
simply need to specify (e.g. in your @file{Mmakefile}) the path prefix
and the list of grades to install:

@example
INSTALL_PREFIX = /my/install/dir
LIBGRADES = asm_fast asm_fast.gc.tr.debug
@end example
@vindex INSTALL_PREFIX
@vindex LIBGRADES

This specifies that libraries should be installed in
@file{/my/install/dir/lib/mercury}, in the default grade plus
@samp{asm_fast} and @samp{asm_fast.gc.tr.debug}.
If @samp{INSTALL_PREFIX} is not specified, @samp{mmake} will attempt to
install the library in the same place as the standard Mercury libraries.
If @samp{LIBGRADES} is not specified, @samp{mmake} will use the Mercury
compiler's default set of grades, which may or may not correspond to the
actual set of grades in which the standard Mercury libraries were installed.

To actually install a library @samp{lib@var{foo}}, use the @samp{mmake}
target @samp{lib@var{foo}.install}.
This also installs all the needed interface files, and (if intermodule
optimisation is enabled) the relevant intermodule optimisation files.

One can override the list of grades to install for a given library
@samp{lib@var{foo}} by setting the @samp{LIBGRADES-@var{foo}} variable,
or add to it by setting @samp{EXTRA_LIBGRADES-@var{foo}}.

The command used to install each file is specified by @samp{INSTALL}.
If @samp{INSTALL} is not specified, @samp{cp} will be used.
@vindex INSTALL

The command used to create directories is specified by @samp{INSTALL_MKDIR}.
If @samp{INSTALL_MKDIR} is not specified, @samp{mkdir -p} will be used.
@vindex INSTALL_MKDIR

Note that currently it is not possible to set the installation prefix
on a library-by-library basis.

@node Using libraries
@section Using libraries
@cindex Libraries, linking with

Once a library is installed, using it is easy.
Suppose the user wishes to use the library @samp{mypackage} (installed
in the tree rooted at @samp{/some/directory/mypackage}) and the library
@samp{myotherlib} (installed in the tree rooted at
@samp{/some/directory/myotherlib}).
The user need only set the following Mmake variables:

@example
EXTRA_LIB_DIRS = /some/directory/mypackage/lib/mercury \
		/some/directory/myotherlib/lib/mercury
EXTRA_LIBRARIES = mypackage myotherlib
@end example
@vindex EXTRA_LIBRARIES
@vindex EXTRA_LIB_DIRS

@findex --intermodule-optimization
When using @samp{--intermodule-optimization} with a library which
uses the C interface, it may be necessary to add @samp{-I} options to
@samp{MGNUCFLAGS} so that the C compiler can find any header files
used by the library's C code.

Mmake will ensure that the appropriate directories are searched for
the relevant interface files, module initialisation files, compiled
libraries, etc.

@findex --mld
@findex --mercury-library-directory
@findex --ml
@findex --mercury-library
To use a library when invoking @samp{mmc} directly, use the @samp{--mld}
and @samp{--ml} options (@pxref{Link options}).

Beware that the directory name that you must use in @samp{EXTRA_LIB_DIRS}
or as the argument of the @samp{--mld} option is not quite the same as
the name that was specified in the @samp{INSTALL_PREFIX} when the library
was installed --- the name needs to have @samp{/lib/mercury} appended.

One can specify extra libraries to be used on a program-by-program
basis.  For instance, if the program @samp{foo} also uses the library
@samp{mylib4foo}, but the other programs governed by the Mmakefile don't,
then one can declare:

@example
EXTRA_LIBRARIES-foo = mylib4foo
@end example

@c ----------------------------------------------------------------------------

@node Debugging
@chapter Debugging
@cindex Debugging
@cindex Tracing
@pindex mdb

@menu
* Quick overview::
* GNU Emacs interface::
* Tracing of Mercury programs::
* Preparing a program for debugging::
* Tracing optimized code::
* Mercury debugger invocation::
* Mercury debugger concepts::
* Debugger commands::
@end menu

@node Quick overview
@section Quick overview

This section gives a quick and simple guide to getting
started with the debugger.  The remainder of this chapter
contains more detailed documentation.

To use the debugger, you must
first compile your program with debugging enabled.
You can do this by using the @samp{--debug} option to @samp{mmc},
or by including @samp{GRADEFLAGS = --debug} in your @file{Mmakefile}.

@findex --debug
@example
bash$ mmc --debug hello.m
@end example

Once you've compiled with debugging enabled, you can use the @samp{mdb}
command to invoke your program under the debugger:

@pindex mdb
@example
bash$ mdb ./hello arg1 arg2 ...
@end example

Any arguments (such as @samp{arg1 arg2 ...} in this example)
that you pass after the program name will be given as arguments
to the program.

The debugger will print a start-up message
and will then show you the first trace event,
namely the call to @code{main/2}:

@example
       1:      1  1 CALL pred hello:main/2-0 (det)
                         hello.m:13
mdb>
@end example

By hitting enter at the @samp{mdb>} prompt, you can step through
the execution of your program to the next trace event:

@example
       2:      2  2 CALL pred io:write_string/3-0 (det)
                         io.m:2837 (hello.m:14)
mdb>
Hello, world
       3:      2  2 EXIT pred io:write_string/3-0 (det)
                         io.m:2837 (hello.m:14)
mdb>

@end example

For each trace event, the debugger prints out several pieces of
information.  The three numbers at the start of the display are the
event number, the call sequence number, and the call depth. 
(You don't really need to pay too much attention to those.)
They are followed by the event type (e.g. @samp{CALL} or @samp{EXIT}).
After that comes the identification of the procedure
in which the event occurred, consisting of the module-qualified name
of the predicate or function to which the procedure belongs,
followed by its arity, mode number and determinism.
This may sometimes be followed by a "path"
(@pxref{Tracing of Mercury programs}).
At the end is the file name and line number of the
called procedure and (if available) also the file name
and line number of the call.

The most useful @code{mdb} commands have single-letter abbreviations.
The @samp{alias} command will show these abbreviations:

@example
mdb> alias
?      =>    help
EMPTY  =>    step
NUMBER =>    step
P      =>    print *
b      =>    break
c      =>    continue
d      =>    stack
f      =>    finish
g      =>    goto
h      =>    help
p      =>    print
r      =>    retry
s      =>    step
v      =>    vars
@end example

The @samp{P} or @samp{print *} command will display the values
of any live variables in scope.
The @samp{f} or @samp{finish} command can be used if you want
to skip over a call.
The @samp{b} or @samp{break} command can be used to set break-points.
The @samp{d} or @samp{stack} command will display the call stack.
The @samp{quit} command will exit the debugger.

That should be enough to get you started.
But if you have GNU Emacs installed, you should strongly
consider using the Emacs interface to @samp{mdb} --- see
the following section.

For more information about the available commands,
use the @samp{?} or @samp{help} command, or see @ref{Debugger commands}.

@node GNU Emacs interface
@section GNU Emacs interface
@cindex GNU Emacs
@cindex Emacs

As well as the command-line debugger, mdb, there is also an Emacs
interface to this debugger.  Note that the Emacs interface only
works with GNU Emacs, not with XEmacs.

With the Emacs interface, the debugger will display your source code
as you trace through it, marking the line that is currently being
executed, and allowing you to easily set breakpoints on particular
lines in your source code.  You can have separate windows for
the debugger prompt, the source code being executed, and for
the output of the program being executed.
In addition, most of the mdb commands are accessible via menus.

To start the Emacs interface, you first need to put the following
text in the file @file{.emacs} in your home directory,
replacing "/usr/local/mercury-1.0" with the directory
that your Mercury implementation was installed in.

@example
(setq load-path (cons (expand-file-name
  "/usr/local/mercury-1.0/lib/mercury/elisp")
  load-path))
(autoload 'mdb "gud" "Invoke the Mercury debugger" t)
@end example

Build your program with debugging enabled, as described
in @ref{Quick overview} or @ref{Preparing a program for debugging}.
Then start up Emacs, e.g. using the command @samp{emacs},
and type @kbd{M-x mdb @key{RET}}. Emacs will then prompt you for
the mdb command to invoke

@example
Run mdb (like this): mdb 
@end example

@noindent
and you should type in the name of the program that you want to debug
and any arguments that you want to pass to it:

@example
Run mdb (like this): mdb ./hello arg1 arg2 ...
@end example

Emacs will then create several "buffers": one for the debugger prompt,
one for the input and output of the program being executed, and one or more
for the source files.  By default, Emacs will split the display into two
parts, called "windows", so that two of these buffers will be visible.
You can use the command @kbd{C-x o} to switch between windows,
and you can use the command @kbd{C-x 2} to split a window into two
windows.  You can use the "Buffers" menu to select which buffer is
displayed in each window.

If you're using X-Windows, then it is a good idea
to set the Emacs variable @samp{pop-up-frames} to @samp{t}
before starting mdb, since this will cause each buffer to be
displayed in a new "frame" (i.e. a new X window).
You can set this variable interactively using the
@samp{set-variable} command, i.e.
@kbd{M-x set-variable @key{RET} pop-up-frames @key{RET} t @key{RET}}.
Or you can put @samp{(setq pop-up-frames t)} in the @file{.emacs}
file in your home directory.

For more information on buffers, windows, and frames,
see the Emacs documentation.

Another useful Emacs variable is @samp{gud-mdb-directories}.
This specifies the list of directories to search for source files.
You can use a command such as

@example
M-x set-variable @key{RET}
gud-mdb-directories @key{RET}
(list "/foo/bar" "../other" "/home/guest") @key{RET}
@end example

@noindent
to set it interactively, or you can put a command like

@example
(setq gud-mdb-directories
  (list "/foo/bar" "../other" "/home/guest"))
@end example

@noindent
in your @file{.emacs} file.

At each trace event, the debugger will search for the
source file corresponding to that event, first in the
same directory as the program, and then in the directories
specified by the @samp{gud-mdb-directories} variable.
It will display the source file, with the line number
corresponding to that trace event marked by
an arrow (@samp{=>}) at the start of the line.

Several of the debugger features can be accessed by moving
the cursor to the relevant part of the source code and then
selecting a command from the menu.
You can set a break point on a line by moving the cursor to the
appropriate line in your source code (e.g. with the arrow keys,
or by clicking the mouse there), and then selecting
the "Set breakpoint on line" command from the "Breakpoints"
sub-menu of the "MDB" menu.  You can set a breakpoint on
a procedure by moving the cursor over the procedure name
and then selecting the "Set breakpoint on procedure"
command from the same menu.  And you can display the value of
a variable by moving the cursor over the variable name
and then selecting the "Print variable" command from the
"Data browsing" sub-menu of the "MDB" menu.
Most of the menu commands also have keyboard short-cuts,
which are displayed on the menu.

Note that mdb's @samp{context} command should not be used if
you are using the Emacs interface, otherwise the Emacs
interface won't be able to parse the file names and
line numbers that mdb outputs, and so it won't be able to
highlight the correct location in the source code.

@node Tracing of Mercury programs
@section Tracing of Mercury programs
@cindex Tracing

The Mercury debugger is based on a modified version of the box model
on which the four-port debuggers of most Prolog systems are based.
Such debuggers abstract the execution of a program
into a sequence, also called a @emph{trace},
of execution events of various kinds.
The four kinds of events supported by most Prolog systems (their @emph{ports})
are

@cindex debugger trace events
@cindex trace events
@cindex call (trace event)
@cindex exit (trace event)
@cindex redo (trace event)
@cindex fail (trace event)
@table @emph
@item call
A call event occurs just after a procedure has been called,
and control has just reached the start of the body of the procedure.
@item exit
An exit event occurs when a procedure call has succeeded,
and control is about to return to its caller.
@item redo
A redo event occurs when all computations
to the right of a procedure call have failed,
and control is about to return to this call
to try to find alternative solutions.
@item fail
A fail event occurs when a procedure call has run out of alternatives,
and control is about to return to the rightmost computation to its left
that still has possibly successful alternatives left.
@end table

Mercury also supports these four kinds of events,
but not all events can occur for every procedure call.
Which events can occur for a procedure call, and in what order,
depend on the determinism of the procedure.
The possible event sequences for procedures of the various determinisms
are as follows.

@table @emph
@item nondet procedures
a call event, zero or more repeats of (exit event, redo event), and a fail event
@item multi procedures
a call event, one or more repeats of (exit event, redo event), and a fail event
@item semidet and cc_nondet procedures
a call event, and either an exit event or a fail event
@item det and cc_multi procedures
a call event and an exit event
@item failure procedures
a call event and a fail event
@item erroneous procedures
a call event
@end table

In addition to these four event types,
Mercury supports @emph{exception} events.
An exception event occurs
when an exception has been thrown inside a procedure,
and control is about to propagate this exception to the caller.
An exception event can replace the final exit or fail event
in the event sequences above
or, in the case of erroneous procedures,
can come after the call event.

Besides the event types call, exit, redo, fail and exception,
which describe the @emph{interface} of a call,
Mercury also supports several types of events
that report on what is happening @emph{internal} to a call.
Each of these internal event types has an associated parameter called a path.
The internal event types are:

@cindex then (trace event)
@cindex else (trace event)
@cindex disj (trace event)
@cindex switch (trace event)
@table @emph
@item then
A then event occurs when execution reaches
the start of the then part of an if-then-else.
The path associated with the event specifies which if-then-else this is.
@item else
An else event occurs when execution reaches
the start of the else part of an if-then-else.
The path associated with the event specifies which if-then-else this is.
@item disj
A disj event occurs when execution reaches
the start of a disjunct in a disjunction.
The path associated with the event specifies
which disjunct of which disjunction this is.
@item switch
A switch event occurs when execution reaches
the start of one arm of a switch
(a disjunction in which each disjunct unifies a bound variable
with different function symbol).
The path associated with the event specifies
which arm of which switch this is.
@c @item pragma_first
@c @item pragma_later
@end table

@cindex path
@cindex goal path
A path is a sequence of path components separated by semicolons.
Each path component is one of the following:

@table @code
@item c@var{num}
The @var{num}'th conjunct of a conjunction.
@item d@var{num}
The @var{num}'th disjunct of a disjunction.
@item s@var{num}
The @var{num}'th arm of a switch.
@item ?
The condition of an if-then-else.
@item t
The then part of an if-then-else.
@item e
The else part of an if-then-else.
@item ~
The goal inside a negation.
@item q
The goal inside an existential quantification.
@end table

A path describes the position of a goal
inside the body of a procedure definition.
For example, if the procedure body is a disjunction
in which each disjunct is a conjunction,
then the path @samp{d2;c3;} denotes the third conjunct
within the second disjunct.
If the third conjunct within the second disjunct is an atomic goal
such as a call or a unification,
then this will be the only goal with whose path has @samp{d2;c3;} as a prefix.
If it is a compound goal,
then its components will all have paths that have @samp{d2;c3;} as a prefix,
e.g. if it is an if-then-else,
then its three components will have the paths
@samp{d2;c3;?;}, @samp{d2;c3;t;} and @samp{d2;c3;e;}.

Paths refer to the internal form of the procedure definition.
When debugging is enabled
(and the option @samp{--trace-optimized} is not given),
the compiler will try to keep this form
as close as possible to the source form of the procedure,
in order to make event paths as useful as possible to the programmer.
Due to the compiler's flattening of terms,
and its introduction of extra unifications to implement calls in implied modes,
the number of conjuncts in a conjunction will frequently differ
between the source and internal form of a procedure.
This is rarely a problem, however, as long as you know about it.
Mode reordering can be a bit more of a problem,
but it can be avoided by writing single-mode predicates and functions
so that producers come before consumers.
The compiler transformation that
potentially causes the most trouble in the interpretation of goal paths
is the conversion of disjunctions into switches.
In most cases, a disjunction is transformed into a single switch,
and it is usually easy to guess, just from the events within a switch arm,
just which disjunct the switch arm corresponds to.
Some cases are more complex;
for example, it is possible for a single disjunction
can be transformed into several switches,
possibly with other, smaller disjunctions inside them.
In such cases, making sense of goal paths
may require a look at the internal form of the procedure.
You can ask the compiler to generate a file
with the internal forms of the procedures in a given module
by including the options @samp{-dfinal -Dpaths} on the command line
when compiling that module.

@node Preparing a program for debugging
@section Preparing a program for debugging

When you compile a Mercury program, you can specify
whether you want to be able to run the Mercury debugger on the program or not.
If you do, the compiler embeds calls to the Mercury debugging system
into the executable code of the program,
at the execution points that represent trace events.
At each event, the debugging system decides
whether to give control back to the executable immediately,
or whether to first give control to you,
allowing you to examine the state of the computation and issue commands.

Mercury supports two broad ways of preparing a program for debugging.
The simpler way is to compile a program in a debugging grade,
which you can do directly by specifying a grade
that includes the word ``debug'' (e.g. @samp{asm_fast.gc.debug}),
or indirectly by specifying the @samp{--debug} grade option
to the compiler, linker, and other tools
(in particular @code{mmc}, @code{mgnuc}, @code{ml}, and @code{c2init}).
If you follow this way,
and accept the default settings of the various compiler options
that control the selection of trace events (which are described below),
you will be assured of being able to get control
at every execution point that represents a potential trace event,
which is very convenient.

The two drawbacks of using a debugging grade
are the large size of the resulting executables,
and the fact that often you discover that you need to debug a big program
only after having built it in a non-debugging grade.
This is why Mercury also supports another way
to prepare a program for debugging,
one that does not require the use of a debugging grade.
With this way, you can decide, individually for each module,
which of three trace levels, @samp{none}, @samp{shallow} and @samp{deep},
you want to compile them with:

@cindex debugger trace level
@cindex trace level
@cindex shallow tracing
@cindex deep tracing
@table @samp
@item none
A procedure compiled with trace level @samp{none}
will never generate any events.
@item deep
A procedure compiled with trace level @samp{deep}
will always generate all the events requested by the user.
By default, this is all possible events,
but you can tell the compiler that
you are not interested in some kinds of events
via compiler options (see below).
@item shallow
A procedure compiled with trace level @samp{shallow}
will generate interface events
if it is called from a procedure compiled with trace level @samp{deep},
but it will never generate any internal events,
and it will not generate any interface events either
if it is called from a procedure compiled with trace level @samp{shallow}.
If it is called from a procedure compiled with trace level @samp{none},
the way it will behave is dictated by whether
its nearest ancestor whose trace level is not @samp{none}
has trace level @samp{deep} or @samp{shallow}.
@end table

The intended uses of these trace levels are as follows.

@table @samp
@item deep
You should compile a module with trace level @samp{deep}
if you suspect there may be a bug in the module,
or if you think that being able to examine what happens inside that module
can help you locate a bug.
@item shallow
You should compile a module with trace level @samp{shallow}
if you believe the code of the module is reliable and unlikely to have bugs,
but you still want to be able to get control at calls to and returns from
any predicates and functions defined in the module,
and if you want to be able to see the arguments of those calls.
@item none
You should compile a module with trace level @samp{none}
only if you are reasonably confident that the module is reliable,
and if you believe that knowing what calls other modules make to this module
would not significantly benefit you in your debugging.
@end table

In general, it is a good idea for most or all modules
that can be called from modules compiled with trace level @samp{deep}
to be compiled with at least trace level @samp{shallow}.

You can control what trace level a module is compiled with
by giving one of the following compiler options:

@table @samp
@item --trace shallow
This always sets the trace level to @samp{shallow}.
@item --trace deep
This always sets the trace level to @samp{deep}.
@item --trace minimum
In debugging grades, this sets the trace level to @samp{shallow};
in non-debugging grades, it sets the trace level to @samp{none}.
@item --trace default
In debugging grades, this sets the trace level to @samp{deep};
in non-debugging grades, it sets the trace level to @samp{none}.
@end table

As the name implies, the fourth alternative is the default,
which is why by default you get
no debugging capability in non-debugging grades
and full debugging capability in debugging grades.
The table also shows that in a debugging grade,
no module can be compiled with trace level @samp{none}.

@strong{Important note}:
If you are not using a debugging grade, but you compile
some modules with @samp{--trace shallow} or @samp{--trace deep},
then you must also pass the @samp{--trace} (or @samp{-t}) option
to c2init and to the Mercury linker.
If you're using Mmake, then you can do this by including @samp{--trace}
in the @samp{MLFLAGS} variable.

If you're using Mmake, then you can also set the compilation options
for a single module named @var{Module} by setting the Mmake variable
@samp{MCFLAGS-@var{Module}}.  For example, to compile the file
@file{foo.m} with deep tracing, @file{bar.m} with shallow tracing,
and everything else with no tracing, you could use the following:

@example
MLFLAGS     = --trace
MCFLAGS-foo = --trace deep
MCFLAGS-bar = --trace shallow
@end example

@node Tracing optimized code
@section Tracing optimized code

@c XXX we should consider where to document --suppress-trace
@c and --stack-trace-higher-order

By default, all trace levels other than @samp{none}
turn off all compiler optimizations
that can affect the sequence of trace events generated by the program,
such as inlining.
If you are specifically interested in
how the compiler's optimizations affect the trace event sequence,
you can specify the option @samp{--trace-optimized},
which tells the compiler that it does not have to disable those optimizations.
(A small number of low-level optimizations
have not yet been enhanced to work properly in the presence of tracing,
so compiler disables these even if @samp{--trace-optimized} is given.)

@node Mercury debugger invocation
@section Mercury debugger invocation

The executables of Mercury programs
by default do not invoke the Mercury debugger
even if some or all of their modules were compiled with some form of tracing,
and even if the grade of the executable is a debugging grade,
This is similar to the behaviour of executables
created by the implementations of other languages;
for example the executable of a C program compiled with @samp{-g}
does not automatically invoke gdb or dbx etc when it is executed.

Unlike those other language implementations,
when you invoke the Mercury debugger @samp{mdb},
you invoke it not just with the name of an executable
but with the command line you want to debug.
If something goes wrong when you execute the command

@example
@var{prog} @var{arg1} @var{arg2} ...
@end example

and you want to find the cause of the problem,
you must execute the command

@example
mdb @var{prog} @var{arg1} @var{arg2} ...
@end example

because you do not get a chance
to specify the command line of the program later.

When the debugger starts up, as part of its initialization
it executes commands from the following three sources, in order:
@enumerate
@item
@vindex MERCURY_DEBUGGER_INIT
The file named by the @samp{MERCURY_DEBUGGER_INIT} environment variable.
Usually, @samp{mdb} sets this variable to point to a file
that provides documentation for all the debugger commands
and defines a small set of aliases.
However, if @samp{MERCURY_DEBUGGER_INIT} is already defined
when @samp{mdb} is invoked, it will leave its value unchanged.
You can use this override ability to provide alternate documentation.
If the file named by @samp{MERCURY_DEBUGGER_INIT} cannot be read,
@samp{mdb} will print a warning,
since in that case, that usual online documentation will not be available.
@item
@cindex mdbrc
@cindex .mdbrc
The file named @samp{.mdbrc} in your home directory.
You can put your usual aliases and settings here.
@item
The file named @samp{.mdbrc} in the current working directory.
You can put program-specific aliases and settings here.
@end enumerate

@node Mercury debugger concepts
@section Mercury debugger concepts

The operation of the Mercury debugger @samp{mdb}
is based on the following concepts.

@table @emph
@item break points
@cindex debugger break points
@cindex break points
@cindex spy points
The user may associate a break point
with some events that occur inside a procedure;
the invocation condition of the break point says which events these are.
The four possible invocation conditions (also called scopes) are:
@sp 1
@itemize @bullet
@item
the call event,
@item
all interface events,
@item
all events, and
@item
the event at a specific point in the procedure.
@end itemize
@sp 1
The effect of a break point depends on the state of the break point.
@sp 1
@itemize @bullet
@item
If the state of the break point is @samp{stop},
execution will stop and user interaction will start
at any event within the procedure that matches the invocation conditions,
unless the current debugger command has specifically disabled this behaviour
(see the concept @samp{strict commands} below).
@sp 1
@item
If the state of the break point is @samp{print},
the debugger will print any event within the procedure
that matches the invocation conditions,
unless the current debugger command has specifically disabled this behaviour
(see the concept @samp{print level} below).
@end itemize
@sp 1
Neither of these will happen if the break point is disabled.
@sp 1
@item strict commands
@cindex strict debugger commands
When a debugger command steps over some events
without user interaction at those events,
the @emph{strictness} of the command controls whether
the debugger will stop execution and resume user interaction
at events to which a break point with state @samp{stop} applies.
By default, the debugger will stop at such events.
However, if the debugger is executing a strict command,
it will not stop at an event
just because a break point in the stop state applies to it.

@cindex debugger interrupt
@cindex interrupt, in debugger
@cindex control-C
If the debugger receives an interrupt (e.g. if the user presses control-C),
it will stop at the next event regardless of what command it is executing
at the time.
@sp 1
@item print level
@cindex print level
@cindex debugger print level
When a debugger command steps over some events
without user interaction at those events,
the @emph{print level} controls under what circumstances
the stepped over events will be printed.
@sp 1
@itemize @bullet
@item
When the print level is @samp{none},
none of the stepped over events will be printed.
@sp 1
@item
When the print level is @samp{all},
all the stepped over events will be printed.
@sp 1
@item
When the print level is @samp{some},
the debugger will print the event only if a break point applies to the event.
@end itemize
@sp 1
Regardless of the print level, the debugger will print
any event that causes execution to stop and user interaction to start.
@sp 1
@item default print level
The debugger maintains a default print level.
The initial value of this variable is @samp{some},
but this value can be overridden by the user.
@sp 1
@item current environment
Whenever execution stops at an event, the current environment
is reset to refer to the stack frame of the call specified by the event.
However, the @samp{up}, @samp{down} and @samp{level} commands
can set the current environment
to refer to one of the ancestors of the current call.
This will then be the current environment until another of these commands
changes the environment yet again or execution continues to another event.
@sp 1
@item procedure specification
@cindex procedure specification (in mdb)
@cindex debugger procedure specification
Some debugger commands, e.g. @samp{break},
require a parameter that specifies a procedure.
Such a procedure specification has
the following components in the following order:
@itemize @bullet
@item
An optional prefix of the form @samp{pred*} or @samp{func*}
that specifies whether the procedure belongs to a predicate or a function.
@item
An optional prefix of the form @samp{@var{module}:} or @samp{@var{module}__}
that specifies the name of the module that defines
the predicate or function to which the procedure belongs.
@item
The name of the predicate or function to which the procedure belongs.
@item
An optional suffix of the form @samp{/@var{arity}}
that specifies the arity of the predicate or function
to which the procedure belongs.
@item
An optional suffix of the form @samp{-@var{modenum}}
that specifies the mode number of the procedure
within the predicate or function to which the procedure belongs.
@end itemize
@end table

@node Debugger commands
@section Debugger commands

When the debugger (as opposed to the program being debugged) is interacting
with the user, the debugger prints a prompt and reads in a line of text,
which it will interpret as its next command line.
A command line consists of a single command,
or several commands separated by semicolons.
Each command consists of several words separated by white space.
The first word is the name of the command,
while any other words give options and/or parameters to the command.

A word may itself contain semicolons or whitespace if it is
enclosed in single quotes (').
This is useful for commands that have other commands as parameters,
for example @samp{view -w 'xterm -e'}.
Characters that have special meaning to @samp{mdb} will be treated like
ordinary charaters if they are escaped with a backslash (\).
It is possible to escape single quotes, whitespace, semicolons, newlines
and the escape character itself.

Some commands take a number as their first parameter.
For such commands, users can type `@var{number} @var{command}'
as well as `@var{command} @var{number}'.
The debugger will treat the former as the latter,
even if the number and the command are not separated by white space.

@menu
* Interactive query commands::
* Forward movement commands::
* Backward movement commands::
* Browsing commands::
* Breakpoint commands::
* Parameter commands::
* Help commands::
* Experimental commands::
* Developer commands::
* Miscellaneous commands::
@end menu

@node Interactive query commands
@subsection Interactive query commands

@table @code
@item query @var{module1} @var{module2} @dots{}
@itemx cc_query @var{module1} @var{module2} @dots{}
@itemx io_query @var{module1} @var{module2} @dots{}
@kindex query (mdb command)
@kindex cc_query (mdb command)
@kindex io_query (mdb command)

@c This documentation has been duplicated in 
@c Opium-M/source/interactive_queries.op so please tell me (jahier@irisa.fr)
@c to update my documentation on interactive queries if you update this 
@c subsection.

These commands allow you to type in queries (goals) interactively
in the debugger.  When you use one of these commands, the debugger
will respond with a query prompt (@samp{?-} or @samp{run <--}),
at which you can type in a goal; the debugger will the compile
and execute the goal and display the answer(s).
You can return from the query prompt to the @samp{mdb>} prompt
by typing the end-of-file indicator (typically control-D or control-Z),
or by typing @samp{quit.}.
@sp 1
The module names @var{module1}, @var{module2}, @dots{} specify
which modules will be imported.  Note that you can also
add new modules to the list of imports directly at the query prompt,
by using a command of the form @samp{[@var{module}]}, e.g. @samp{[int]}.
You need to import all the modules that define symbols used in your query.
Queries can only use symbols that are exported from a module;
entities which are declared in a module's implementation section
only cannot be used.
@sp 1
The three variants differ in what kind of goals they allow. 
For goals which perform I/O, you need to use @samp{io_query};
this lets you type in the goal using DCG syntax.
For goals which don't do I/O, but which have determinism
@samp{cc_nondet} or @samp{cc_multi}, you need to use @samp{cc_query};
this finds only one solution to the specified goal.
For all other goals, you can use plain @samp{query}, which
finds all the solutions to the goal.
@sp 1
For @samp{query} and @samp{cc_query}, the debugger will print
out all the variables in the goal using @samp{io__write}.
The goal must bind all of its variables to ground terms,
otherwise you will get a mode error.
@sp 1
The current implementation works by compiling the queries on-the-fly
and then dynamically linking them into the program being debugged.
Thus it may take a little while for your query to be executed.
Each query will be written to a file named @file{query.m} in the current
directory, so make sure you don't name your source file @file{query.m}.
Note that dynamic linking may not be supported on some systems;
if you are using a system for which dynamic linking is not supported,
you will get an error message when you try to run these commands.
@sp 1
You may also need to build your program using shared libraries
for interactive queries to work.
With Linux on the Intel x86 architecture, the default is for
executables to be statically linked, which means that dynamic
linking won't work, and hence interactive queries won't work either
(the error message is rather obscure: the dynamic linker complains
about the symbol @samp{__data_start} being undefined).
To build with shared libraries, you can use
@samp{MGNUCFLAGS=--pic-reg} and @samp{MLFLAGS=--shared} in your
Mmakefile.  See the @file{README.Linux} file in the Mercury
distribution for more details.

@end table

@node Forward movement commands
@subsection Forward movement commands

@table @code
@item step [-NSans] [@var{num}]
@kindex step (mdb command)
Steps forward @var{num} events.
If this command is given at event @var{cur}, continues execution until
event @var{cur} + @var{num}. The default value of @var{num} is 1.
@sp 1
The options @samp{-n} or @samp{--none}, @samp{-s} or @samp{--some},
@samp{-a} or @samp{--all} specify the print level to use
for the duration of the command,
while the options @samp{-S} or @samp{--strict}
and @samp{-N} or @samp{--nostrict} specify
the strictness of the command.
@sp 1
By default, this command is not strict, and it uses the default print level.
@sp 1
A command line containing only a number @var{num} is interpreted as
if it were `step @var{num}'.
@sp 1
An empty command line is interpreted as `step 1'.
@sp 1
@item goto [-NSans] @var{num}
@kindex goto (mdb command)
Continues execution until the program reaches event number @var{num}.
If the current event number is larger than @var{num}, it reports an error.
@sp 1
The options @samp{-n} or @samp{--none}, @samp{-s} or @samp{--some},
@samp{-a} or @samp{--all} specify the print level to use
for the duration of the command,
while the options @samp{-S} or @samp{--strict}
and @samp{-N} or @samp{--nostrict} specify
the strictness of the command.
@sp 1
By default, this command is strict, and it uses the default print level.
@sp 1
@item next [-NSans] [@var{num}]
@kindex next (mdb command)
Continues execution until it reaches the next event of
the @var{num}'th ancestor of the call to which the current event refers.
The default value of @var{num} is zero,
which means skipping to the next event of the current call.
Reports an error if execution is already at the end of the specified call.
@sp 1
The options @samp{-n} or @samp{--none}, @samp{-s} or @samp{--some},
@samp{-a} or @samp{--all} specify the print level to use
for the duration of the command,
while the options @samp{-S} or @samp{--strict}
and @samp{-N} or @samp{--nostrict} specify
the strictness of the command.
@sp 1
By default, this command is strict, and it uses the default print level.
@sp 1
@item finish [-NSans] [@var{num}]
@kindex finish (mdb command)
Continues execution until it reaches a final (EXIT, FAIL or EXCP) port
of the @var{num}'th ancestor of the call to which the current event refers.
The default value of @var{num} is zero,
which means skipping to the end of the current call.
Reports an error if execution is already at the desired port.
@sp 1
The options @samp{-n} or @samp{--none}, @samp{-s} or @samp{--some},
@samp{-a} or @samp{--all} specify the print level to use
for the duration of the command,
while the options @samp{-S} or @samp{--strict}
and @samp{-N} or @samp{--nostrict} specify
the strictness of the command.
@sp 1
By default, this command is strict, and it uses the default print level.
@c The documentation of fail is commented out, because the implementation does
@c not yet do this right thing when the procedure call we want to get to the
@c FAIL port of is inside a commit.
@c @sp 1
@c @item fail [-NSans] [@var{num}]
@c Continues execution until it reaches a FAIL or EXCP port
@c of the @var{num}'th ancestor of the call to which the current event refers.
@c The default value of @var{num} is zero,
@c which means skipping to the end of the current call.
@c Reports an error if execution is already at the desired port,
@c or if the determinism of the selected call
@c does not guarantee that it will eventually fail.
@c @sp 1
@c The options @samp{-n} or @samp{--none}, @samp{-s} or @samp{--some},
@c @samp{-a} or @samp{--all} specify the print level to use
@c for the duration of the command,
@c while the options @samp{-S} or @samp{--strict}
@c and @samp{-N} or @samp{--nostrict} specify
@c the strictness of the command.
@c @sp 1
@c By default, this command is strict, and it uses the default print level.
@sp 1
@item exception [-NSans]
@kindex exception (mdb command)
Continues the program until execution reaches an exception event.
Reports an error if the current event is already an exception event.
@sp 1
The options @samp{-n} or @samp{--none}, @samp{-s} or @samp{--some},
@samp{-a} or @samp{--all} specify the print level to use
for the duration of the command,
while the options @samp{-S} or @samp{--strict}
and @samp{-N} or @samp{--nostrict} specify
the strictness of the command.
@sp 1
By default, this command is strict, and it uses the default print level.
@sp 1
@item return [-NSans]
@kindex return (mdb command)
Continues the program until the program finished returning,
i.e. until it reaches a port other than EXIT.
Reports an error if the current event already refers to such a port.
@sp 1
The options @samp{-n} or @samp{--none}, @samp{-s} or @samp{--some},
@samp{-a} or @samp{--all} specify the print level to use
for the duration of the command,
while the options @samp{-S} or @samp{--strict}
and @samp{-N} or @samp{--nostrict} specify
the strictness of the command.
@sp 1
By default, this command is strict, and it uses the default print level.
@sp 1
@item forward [-NSans]
@kindex forward (mdb command)
Continues the program until the program resumes forward execution,
i.e. until it reaches a port other than REDO or FAIL.
Reports an error if the current event already refers to such a port.
@sp 1
The options @samp{-n} or @samp{--none}, @samp{-s} or @samp{--some},
@samp{-a} or @samp{--all} specify the print level to use
for the duration of the command,
while the options @samp{-S} or @samp{--strict}
and @samp{-N} or @samp{--nostrict} specify
the strictness of the command.
@sp 1
By default, this command is strict, and it uses the default print level.
@sp 1
@item mindepth [-NSans] @var{depth}
@kindex mindepth (mdb command)
Continues the program until the program reaches an event
whose depth is at least @var{depth}.
Reports an error if the current event already refers to such a port.
@sp 1
The options @samp{-n} or @samp{--none}, @samp{-s} or @samp{--some},
@samp{-a} or @samp{--all} specify the print level to use
for the duration of the command,
while the options @samp{-S} or @samp{--strict}
and @samp{-N} or @samp{--nostrict} specify
the strictness of the command.
@sp 1
By default, this command is strict, and it uses the default print level.
@sp 1
@item maxdepth [-NSans] @var{depth}
@kindex maxdepth (mdb command)
Continues the program until the program reaches an event
whose depth is at most @var{depth}.
Reports an error if the current event already refers to such a port.
@sp 1
The options @samp{-n} or @samp{--none}, @samp{-s} or @samp{--some},
@samp{-a} or @samp{--all} specify the print level to use
for the duration of the command,
while the options @samp{-S} or @samp{--strict}
and @samp{-N} or @samp{--nostrict} specify
the strictness of the command.
@sp 1
By default, this command is strict, and it uses the default print level.
@sp 1
@item continue [-NSans]
@kindex continue (mdb command)
Continues execution until it reaches the end of the program.
@sp 1
The options @samp{-n} or @samp{--none}, @samp{-s} or @samp{--some},
@samp{-a} or @samp{--all} specify the print level to use
for the duration of the command,
while the options @samp{-S} or @samp{--strict}
and @samp{-N} or @samp{--nostrict} specify
the strictness of the command.
@sp 1
By default, this command is not strict. The print level used
by the command by default depends on the final strictness level:
if the command is strict, it is @samp{none}, otherwise it is @samp{some}.
@end table
@sp 1
@node Backward movement commands
@subsection Backward movement commands
@sp 1
@table @code
@item retry
@kindex retry (mdb command)
Restarts execution at the call port
of the call corresponding to the current event.
@sp 1
The command will report an error unless
the values of all the input arguments are available at the current port.
(The compiler will keep the values
of the input arguments of traced predicates as long as possible,
but it cannot keep them beyond the point where they are destructively updated.)
@c XXX THE EXCEPTION IS NOT YET IMPLEMENTED.
@c The exception is values of type `io__state';
@c the debugger can perform a retry if the only missing value is of
@c type `io__state' (there can be only one io__state at any given time).
@c @sp 1
@c A retry in which the values of all input arguments are available
@c works fine, provided that the predicates defined in C code that are
@c called inside the repeated computation do not pose any problems.
@c A retry in which a value of type `io__state' is missing has the
@c following effects:
@c @sp 1
@c @itemize @bullet
@c @item
@c Any input and/or output actions in the repeated code will be repeated.
@c @item
@c Any file close actions in the repeated code
@c for which the corresponding file open action is not also in the repeated code
@c may cause later I/O actions referring to the file to fail.
@c @item
@c Any file open actions in the repeated code
@c for which the corresponding file close action
@c is not also in the repeated code
@c may cause later file open actions to fail due to file descriptor leak.
@c @end itemize
@sp 1
The debugger can perform a retry only from an exit or fail port;
only at these ports does the debugger have enough information
to figure out how to reset the stacks.
If the debugger is not at such a port when a retry command is given,
the debugger will continue forward execution
until it reaches an exit or fail port of the call to be retried
before it performs the retry.
This may require a noticeable amount of time.
@c XXX not yet
@c and may result in the execution of I/O and/or other side-effects.
@sp 1
@item retry @var{num}
Restarts execution at the call port of the call corresponding to
the @var{num}'th ancestor of the call to which the current event belongs.
For example, if @var{num} is 1, it restarts the parent of the current call.
@end table
@sp 1
@node Browsing commands
@subsection Browsing commands
@sp 1
@table @code
@item vars
@kindex vars (mdb command)
Prints the names of all the known variables in the current environment,
together with an ordinal number for each variable.
@sp 1
@item print [-fpv] @var{name}
@itemx print [-fpv] @var{num}
@kindex print (mdb command)
Prints the value of the variable in the current environment
with the given name, or with the given ordinal number.
This is a non-interactive version of the @samp{browse}
command (see below).  Various settings
which affect the way that terms are printed out
(including e.g. the maximum term depth) can be set using
the @samp{set} command.
@sp 1
The options @samp{-f} or @samp{--flat}, @samp{-p} or @samp{--pretty},
and @samp{-v} or @samp{--verbose} specify the format to use for printing.
@sp 1
@item print [-fpv] *
Prints the values of all the known variables in the current environment.
@sp 1
The options @samp{-f} or @samp{--flat}, @samp{-p} or @samp{--pretty},
and @samp{-v} or @samp{--verbose} specify the format to use for printing.
@sp 1
@item print [-fpv]
@item print [-fpv] goal
Prints the goal of the current call in its present state of instantiation.
@sp 1
The options @samp{-f} or @samp{--flat}, @samp{-p} or @samp{--pretty},
and @samp{-v} or @samp{--verbose} specify the format to use for printing.
@sp 1
@item print [-fpv] exception
Prints the value of the exception at an EXCP port.
Reports an error if the current event does not refer to such a port.
@sp 1
The options @samp{-f} or @samp{--flat}, @samp{-p} or @samp{--pretty},
and @samp{-v} or @samp{--verbose} specify the format to use for printing.
@sp 1
@item browse [-fpv] @var{name}
@itemx browse [-fpv] @var{num}
@kindex browse (mdb command)
Invokes an interactive term browser to browse
the value of the variable in the current environment
with the given ordinal number or with the given name.
@sp 1
The interactive term browser allows you
to selectively examine particular subterms. 
The depth and size of printed terms
may be controlled. 
The displayed terms may also be clipped to fit
within a single screen.
@sp 1
The options @samp{-f} or @samp{--flat}, @samp{-p} or @samp{--pretty},
and @samp{-v} or @samp{--verbose} specify the format to use for browsing.
@sp 1
For further documentation on the interactive term browser,
invoke the @samp{browse} command from within @samp{mdb} and then
type @samp{help} at the @samp{browser>} prompt.
@sp 1
@item browse [-fpv]
@item browse [-fpv] goal
Invokes the interactive term browser to browse
the goal of the current call in its present state of instantiation.
@sp 1
The options @samp{-f} or @samp{--flat}, @samp{-p} or @samp{--pretty},
and @samp{-v} or @samp{--verbose} specify the format to use for browsing.
@sp 1
@item browse [-fpv] exception
Invokes the interactive term browser to browse
the value of the exception at an EXCP port.
Reports an error if the current event does not refer to such a port.
@sp 1
The options @samp{-f} or @samp{--flat}, @samp{-p} or @samp{--pretty},
and @samp{-v} or @samp{--verbose} specify the format to use for browsing.
@sp 1
@item stack [-d]
@kindex stack (mdb command)
Prints the names of the ancestors of the call
specified by the current event.
If two or more ancestor calls are for the same procedure,
the procedure identification will be printed once
with the appropriate multiplicity annotation.
@sp 1
The option @samp{-d} or @samp{--detailed}
specifies that for each ancestor call,
the call's event number, sequence number and depth should also be printed
if the call is to a procedure that is being execution traced.
@sp 1
This command will report an error if there is no stack trace
information available about any ancestor.
@sp 1
@item up [-d] [@var{num}]
@kindex up (mdb command)
Sets the current environment to the stack frame
of the @var{num}'th level ancestor of the current environment
(the immediate caller is the first-level ancestor).
@sp 1
If @var{num} is not specified, the default value is one.
@sp 1
This command will report an error
if the current environment doesn't have the required number of ancestors,
or if there is no execution trace information about the requested ancestor,
or if there is no stack trace information about any of the ancestors
between the current environment and the requested ancestor.
@sp 1
The option @samp{-d} or @samp{--detailed}
specifies that for each ancestor call,
the call's event number, sequence number and depth should also be printed
if the call is to a procedure that is being execution traced.
@sp 1
@item down [-d] [@var{num}]
@kindex down (mdb command)
Sets the current environment to the stack frame
of the @var{num}'th level descendant of the current environment
(the procedure called by the current environment
is the first-level descendant).
@sp 1
If @var{num} is not specified, the default value is one.
@sp 1
This command will report an error
if there is no execution trace information about the requested descendant.
@sp 1
The option @samp{-d} or @samp{--detailed}
specifies that for each ancestor call,
the call's event number, sequence number and depth should also be printed
if the call is to a procedure that is being execution traced.
@sp 1
@item level [-d] [@var{num}]
@kindex level (mdb command)
Sets the current environment to the stack frame of the @var{num}'th
level ancestor of the call to which the current event belongs.
The zero'th ancestor is the call of the event itself.
@sp 1
This command will report an error
if the current environment doesn't have the required number of ancestors,
or if there is no execution trace information about the requested ancestor,
or if there is no stack trace information about any of the ancestors
between the current environment and the requested ancestor.
@sp 1
The option @samp{-d} or @samp{--detailed}
specifies that for each ancestor call,
the call's event number, sequence number and depth should also be printed
if the call is to a procedure that is being execution traced.
@sp 1
@item current
@kindex current (mdb command)
Prints the current event.
This is useful if the details of the event,
which were printed when control arrived at the event,
have since scrolled off the screen.
@sp 1
@item set [-APBfpv] @var{param} @var{value}
@kindex set (mdb command)
@kindex format (mdb command)
@kindex depth (mdb command)
@kindex size (mdb command)
@kindex width (mdb command)
@kindex lines (mdb command)
Updates the configuration parameters of the browser.
The parameters that can be configured are
@samp{format}, @samp{depth}, @samp{size}, @samp{width} and @samp{lines}.
@sp 1
@itemize @bullet
@item
@samp{format} can be set to @samp{flat}, @samp{pretty} or @samp{verbose}
to change the output style of the browser.
@sp 1
@item
@samp{depth} is the maximum depth to which subterms will be displayed.
@sp 1
@item
@samp{size} is the suggested maximum number of functors to display.
Beyond this limit, the browser will abbreviate the output.
@sp 1
@item
@samp{width} is the width of the screen in characters.
@sp 1
@item
@samp{lines} is the maximum number of lines of one term to display.
@end itemize
@sp 1
The browser maintains separate configuration parameters
for the three commands @samp{print *}, @samp{print @var{var}},
and @samp{browse @var{var}}.
A single @samp{set} command can modify the parameters
for more than one of these;
the options @samp{-A} or @samp{--print-all}, @samp{-P} or @samp{--print},
and @samp{-B} or @samp{--browse}
select which commands will be affected by the change.
If none of these options is given,
the default is to affect all commands.
@sp 1
The browser also maintains separate configuration parameters
for the three different output formats.
This applies to all parameters except for the format itself.
The options @samp{-f} or @samp{--flat}, @samp{-p} or @samp{--pretty},
and @samp{-v} or @samp{--verbose}
select which formats will be affected by the change.
If none of these options is given,
the default is to affect all formats.
In the case that the format itself is being set,
these options are ignored.
@sp 1
@item view [-vf2] [-w @var{window-cmd}] [-s @var{server-cmd}] [-n @var{server-name}] [-t @var{timeout}]
@itemx view -c [-v] [-s @var{server-cmd}] [-n @var{server-name}]
@kindex view (mdb command)
Opens a new window displaying the source code,
at the location of the current event.
As mdb stops at new events,
the window is updated to track through the source code.
This requires X11 and a version of @samp{vim}
compiled with the client/server option enabled.
@sp 1
The debugger only updates one window at a time.
If you try to open a new source window when there is already one open,
this command aborts with an error message.
@sp 1
The variant with @samp{-c} (or @samp{--close})
does not open a new window but instead
attempts to close a currently open source window.
The attempt may fail if, for example,
the user has modified the source file without saving.
@sp 1
The option @samp{-v} (or @samp{--verbose})
prints the underlying system calls before running them,
and prints any output the calls produced.
This is useful to find out what is wrong if the server does not start.
@sp 1
The option @samp{-f} (or @samp{--force})
stops the command from aborting if there is already a window open.
Instead it attempts to close that window first.
@sp 1
The option @samp{-2} (or @samp{--split-screen})
starts the vim server with two windows,
which allows both the callee as well as the caller
to be displayed at interface events.
The lower window shows what would normally be seen
if the split-screen option was not used,
which at interface events is the caller.
At these events,
the upper window shows the callee definition.
At internal events,
the lower window shows the associated source,
and the view in the upper window
(which is not interesting at these events)
remains unchanged.
@sp 1
The option @samp{-w} (or @samp{--window-command}) specifies
the command to open a new window.
The default is @samp{xterm -e}.
@sp 1
The option @samp{-s} (or @samp{--server-command}) specifies
the command to start the server.
The default is @samp{vim}.
@sp 1
The option @samp{-n} (or @samp{--server-name}) specifies
the name of an existing server.
Instead of starting up a new server,
mdb will attempt to connect to the existing one.
@sp 1
The option @samp{-t} (or @samp{--timeout}) specifies
the maximum number of seconds to wait for the server to start.
@end table
@sp 1
@node Breakpoint commands
@subsection Breakpoint commands
@cindex Breakpoints
@sp 1
@table @code
@item break [-PS] [-E@var{ignore-count}] [-I@var{ignore-count}] @var{filename}:@var{linenumber}
@kindex break (mdb command)
Puts a break point on the specified line of the specified source file,
if there is an event or a call at that position.
If the filename is omitted,
it defaults to the filename from the context of the current event.
@sp 1
The options @samp{-P} or @samp{--print}, and @samp{-S} or @samp{--stop}
specify the action to be taken at the break point.
@sp 1
The options @samp{-E@var{ignore-count}}
and @samp{--ignore-entry @var{ignore-count}}
tell the debugger to ignore the breakpoint
until after @var{ignore-count} occurrences of a call event
that matches the breakpoint.
The options @samp{-I@var{ignore-count}}
and @samp{--ignore-interface @var{ignore-count}}
tell the debugger to ignore the breakpoint
until after @var{ignore-count} occurrences of interface events
that match the breakpoint.
@sp 1
By default, the initial state of the break point is @samp{stop},
and the ignore count is zero.
@item break [-AOPSaei] [-E@var{ignore-count}] [-I@var{ignore-count}] @var{proc-spec}
@c <module name> <predicate name> [<arity> [<mode> [<predfunc>]]]
Puts a break point on the specified procedure.
@sp 1
The options @samp{-A} or @samp{--select-all},
and @samp{-O} or @samp{--select-one}
select the action to be taken
if the specification matches more than one procedure.
If you have specified option @samp{-A} or @samp{--select-all},
mdb will put a breakpoint on all matched procedures,
whereas if you have specified option @samp{-O} or @samp{--select-one},
mdb will report an error.
By default, mdb will ask you whether you want to put a breakpoint
on all matched procedures or just one, and if so, which one.
@sp 1
The options @samp{-P} or @samp{--print}, and @samp{-S} or @samp{--stop}
specify the action to be taken at the break point.
@sp 1
The options @samp{-a} or @samp{--all},
@samp{-e} or @samp{--entry}, and @samp{-i} or @samp{--interface}
specify the invocation conditions of the break point.
If none of these options are specified,
the default is the one indicated by the current scope
(see the @samp{scope} command below).
The initial scope is @samp{interface}.
@sp 1
The options @samp{-E@var{ignore-count}}
and @samp{--ignore-entry @var{ignore-count}}
tell the debugger to ignore the breakpoint
until after @var{ignore-count} occurrences of a call event
that matches the breakpoint.
The options @samp{-I@var{ignore-count}}
and @samp{--ignore-interface @var{ignore-count}}
tell the debugger to ignore the breakpoint
until after @var{ignore-count} occurrences of interface events
that match the breakpoint.
@sp 1
By default, the action of the break point is @samp{stop},
its invocation condition is @samp{interface},
and the ignore count is zero.
@sp 1
@item break [-PS] [-E@var{ignore-count}] [-I@var{ignore-count}] here
Puts a break point on the procedure referred to by the current event,
with the invocation condition being the event at the current location
in the procedure body.
@sp 1
The options @samp{-P} or @samp{--print}, and @samp{-S} or @samp{--stop}
specify the action to be taken at the break point.
@sp 1
The options @samp{-E@var{ignore-count}}
and @samp{--ignore-entry @var{ignore-count}}
tell the debugger to ignore the breakpoint
until after @var{ignore-count} occurrences of a call event
that matches the breakpoint.
The options @samp{-I@var{ignore-count}}
and @samp{--ignore-interface @var{ignore-count}}
tell the debugger to ignore the breakpoint
until after @var{ignore-count} occurrences of interface events
that match the breakpoint.
@sp 1
By default, the initial state of the break point is @samp{stop},
and the ignore count is zero.
@sp 1
@item break info
Lists the details and status of all break points.
@sp 1
@item ignore [-E@var{ignore-count}] [-I@var{ignore-count}] @var{num}
@sp 1
The options @samp{-E@var{ignore-count}}
and @samp{--ignore-entry @var{ignore-count}}
tell the debugger to ignore the breakpoint
until after @var{ignore-count} occurrences of a call event
that matches the breakpoint with the specified number.
The options @samp{-I@var{ignore-count}}
and @samp{--ignore-interface @var{ignore-count}}
tell the debugger to ignore the breakpoint
until after @var{ignore-count} occurrences of interface events
that match the breakpoint with the specified number.
If neither option is given,
the default is to ignore one call event
that matches the breakpoint with the specified number.
Reports an error if there is no break point with the specified number.
@sp 1
@item ignore [-E@var{ignore-count}] [-I@var{ignore-count}]
@sp 1
The options @samp{-E@var{ignore-count}}
and @samp{--ignore-entry @var{ignore-count}}
tell the debugger to ignore the breakpoint
until after @var{ignore-count} occurrences of a call event
that matches the most recently added breakpoint.
The options @samp{-I@var{ignore-count}}
and @samp{--ignore-interface @var{ignore-count}}
tell the debugger to ignore the breakpoint
until after @var{ignore-count} occurrences of interface events
that match the most recently added breakpoint.
If neither option is given,
the default is to ignore one call event
that matches the most recently added breakpoint.
Reports an error if the most recently added breakpoint has since been deleted.
@sp 1
@item disable @var{num}
@kindex disable (mdb command)
Disables the break point with the given number.
Reports an error if there is no break point with that number.
@sp 1
@item disable *
Disables all break points.
@sp 1
@item disable
Disables the most recently added breakpoint.
Reports an error if the most recently added breakpoint has since been deleted.
@sp 1
@item enable @var{num}
Enables the break point with the given number.
Reports an error if there is no break point with that number.
@sp 1
@item enable *
@kindex enable (mdb command)
Enables all break points.
@sp 1
@item enable
Enables the most recently added breakpoint.
Reports an error if the most recently added breakpoint has since been deleted.
@sp 1
@item delete @var{num}
@kindex delete (mdb command)
Deletes the break point with the given number.
Reports an error if there is no break point with that number.
@sp 1
@item delete *
Deletes all break points.
@sp 1
@item delete
Deletes the most recently added breakpoint.
Reports an error if the most recently added breakpoint
has already been deleted.
@sp 1
@item modules
@kindex modules (mdb command)
Lists all the debuggable modules
(i.e. modules that have debugging information).
@sp 1
@item procedures @var{module}
@kindex procedures (mdb command)
Lists all the procedures in the debuggable module @var{module}.
@sp 1
@item register
@kindex register (mdb command)
Registers all debuggable modules with the debugger.
Has no effect if this registration has already been done.
The debugger will perform this registration when creating breakpoints
and when listing debuggable modules and/or procedures.
@end table
@sp 1
@node Parameter commands
@subsection Parameter commands
@sp 1
@table @code
@item mmc_options @var{option1} @var{option2} @dots{}
@kindex mmc_options (mdb command)
This command sets the options that will be passed to @samp{mmc}
to compile your query when you use one of the query commands:
@samp{query}, @samp{cc_query}, or @samp{io_query}.
For example, if a query results in a compile error,
it may sometimes be helpful to use @samp{mmc_options --verbose-error-messages}.
@sp 1
@item printlevel none
@kindex printlevel (mdb command)
Sets the default print level to @samp{none}.
@sp 1
@item printlevel some
Sets the default print level to @samp{some}.
@sp 1
@item printlevel all
Sets the default print level to @samp{all}.
@sp 1
@item printlevel
Reports the current default print level.
@sp 1
@item echo on
@kindex echo (mdb command)
Turns on the echoing of commands.
@sp 1
@item echo off
Turns off the echoing of commands.
@sp 1
@item echo
Reports whether commands are being echoed or not.
@sp 1
@item scroll on
@kindex scroll (mdb command)
Turns on user control over the scrolling of sequences of event reports.
This means that every screenful of event reports
will be followed by a @samp{--more--} prompt.
You may type an empty line, which allows the debugger
to continue to print the next screenful of event reports.
By typing a line that starts with @samp{a}, @samp{s} or @samp{n},
you can override the print level of the current command,
setting it to @samp{all}, @samp{some} or @samp{none} respectively.
By typing a line that starts with @samp{q},
you can abort the current debugger command
and get back control at the next event.
@sp 1
@item scroll off
Turns off user control over the scrolling of sequences of event reports.
@sp 1
@item scroll @var{size}
Sets the scroll window size to @var{size},
which tells scroll control to stop and print a @samp{--more--} prompt
after every @var{size - 1} events.
The default value of @var{size}
is the value of the @samp{LINES} environment variable,
which should correspond to the number of lines available on the terminal.
@sp 1
@item scroll
Reports whether user scroll control is enabled and what the window size is.
@sp 1
@item context none
@kindex context (mdb command)
@cindex line numbers
@cindex file names
When reporting events or ancestor levels,
does not print contexts (filename/line number pairs).
@sp 1
@item context before
When reporting events or ancestor levels,
prints contexts (filename/line number pairs)
before the identification of the event or call to which they refer,
on the same line.
With long fully qualified predicate and function names,
this may make the line wrap around.
@sp 1
@item context after
When reporting events or ancestor levels,
prints contexts (filename/line number pairs)
after the identification of the event or call to which they refer,
on the same line.
With long fully qualified predicate and function names,
this may make the line wrap around.
@sp 1
@item context prevline
When reporting events or ancestor levels,
prints contexts (filename/line number pairs) on a separate line
before the identification of the event or call to which they refer.
@sp 1
@item context nextline
When reporting events or ancestor levels,
prints contexts (filename/line number pairs) on a separate line
after the identification of the event or call to which they refer.
@sp 1
@item context
Reports where contexts are being printed.
@sp 1
@item scope all
Sets the default scope of new breakpoints to "all",
i.e. by default, new breakpoints on procedures
will stop at all events in the procedure.
@sp 1
@item scope interface
Sets the default scope of new breakpoints to "interface",
i.e. by default, new breakpoints on procedures
will stop at all interface events in the procedure.
@sp 1
@item scope entry
Sets the default scope of new breakpoints to "entry",
i.e. by default, new breakpoints on procedures
will stop only at events representing calls to the procedure.
@sp 1
@item scope
Reports the current default scope of new breakpoints.
@sp 1
@item alias @var{name} @var{command} [@var{command-parameter} ...]
@kindex alias (mdb command)
Introduces @var{name} as an alias
for the given command with the given parameters.
Whenever a command line has @var{name} as its first word,
the debugger will substitute the given command and parameters for this word
before executing the command line.
@sp 1
If @var{name} is the upper-case word @samp{EMPTY},
the debugger will substitute the given command and parameters
whenever the user types in an empty command line.
@sp 1
@sp 1
If @var{name} is the upper-case word @samp{NUMBER},
the debugger will insert the given command and parameters
before the command line
whenever the user types in a command line that consists of a single number.
@sp 1
@item unalias @var{name}
@kindex unalias (mdb command)
Removes any existing alias for @var{name}.
@end table
@sp 1
@node Help commands
@subsection Help commands
@sp 1
@table @code
@item document_category @var{slot} @var{category}
@kindex document_category (mdb command)
Create a new category of help items, named @var{category}.
The summary text for the category is given by the lines following this command,
up to but not including a line containing only the lower-case word @samp{end}.
The list of category summaries printed in response to the command @samp{help}
is ordered on the integer @var{slot} numbers of the categories involved.
@sp 1
@item document @var{category} @var{slot} @var{item}
@kindex document (mdb command)
Create a new help item named @var{item} in the help category @var{category}.
The text for the help item is given by the lines following this command,
up to but not including a line containing only the lower-case word @samp{end}.
The list of items printed in response to the command @samp{help @var{category}}
is ordered on the integer @var{slot} numbers of the items involved.
@sp 1
@item help @var{category} @var{item}
@kindex help (mdb command)
Prints help text about the item @var{item} in category @var{category}.
@sp 1
@item help @var{word}
Prints help text about @var{word},
which may be the name of a help category or a help item.
@sp 1
@item help
Prints summary information about all the available help categories.
@end table
@sp 1
@node Experimental commands
@subsection Experimental commands
@sp 1
@table @code
@item histogram_all @var{filename}
@kindex histogram_all (mdb command)
Prints (to file @var{filename})
a histogram that counts all events at various depths
since the start of the program.
This histogram is available
only in some experimental versions of the Mercury runtime system.
@sp 1
@item histogram_exp @var{filename}
@kindex histogram_exp (mdb command)
Prints (to file @var{filename})
a histogram that counts all events at various depths
since the start of the program or since the histogram was last cleared.
This histogram is available
only in some experimental versions of the Mercury runtime system.
@sp 1
@item clear_histogram
@kindex clear_histogram (mdb command)
Clears the histogram printed by @samp{histogram_exp},
i.e. sets the counts for all depths to zero.
@end table
@node Developer commands
@subsection Developer commands
@sp 1
The following commands are intended for use by the developers
of the Mercury implementation.
@sp 1
@table @code
@item nondet_stack [-d]
@kindex nondet_stack (mdb command)
Prints the contents of the frames on the nondet stack.
By default, it prints only of the fixed slots in each nondet stack frame,
but if the option @samp{-d} or @samp{--detailed} option is given,
it will also print the names and values of the live variables in them.
@sp 1
@item stack_regs
@kindex stack_regs (mdb command)
Prints the contents of the virtual machine registers
that point to the det and nondet stacks.
@sp 1
@item all_regs
@kindex all_regs (mdb command)
Prints the contents of all the virtual machine registers.
@sp 1
@item table_io
@kindex table_io (mdb command)
Reports which phase of I/O tabling we are in at the moment.
@sp 1
@item table_io stats
Reports statistics about I/O tabling.
@sp 1
@item table_io start
Tells the debugger to start tabling I/O actions.
@sp 1
@item table_io end
Tells the debugger to stop tabling I/O actions.
@sp 1
@item proc_stats
@kindex proc_stats (mdb command)
Prints statistics about proc layout structures in the program.
@sp 1
@item proc_stats @var{filename}
Prints statistics about proc layout structures in the program
to the file @var{filename}.
@sp 1
@item label_stats
@kindex label_stats (mdb command)
Prints statistics about label layout structures in the program.
@sp 1
@item label_stats @var{filename}
Prints statistics about label layout structures in the program
to the file @var{filename}.
@sp 1
@item print_optionals
@kindex print_optionals (mdb command)
Reports whether optionally-printed values such as typeinfos
that are usually of interest only to implementors are being printed or not.
@sp 1
@item print_optionals on
Tells the debugger to print optionally-printed values.
@sp 1
@item print_optionals off
Tells the debugger not to print optionally-printed values.
@end table
@node Miscellaneous commands
@subsection Miscellaneous commands
@sp 1
@table @code
@item source [-i] @var{filename}
@kindex source (mdb command)
Executes the commands in the file named @var{filename}.
@sp 1
The option @samp{-i} or @samp{--ignore-errors} tells @samp{mdb}
not to complain if the named file does not exist or is not readable.
@sp 1
@item save @var{filename}
@kindex save (mdb command)
Saves current set of breakpoints and the current set of aliases
in the named file as a set of @samp{break} and @samp{alias} commands.
Sourcing the file will recreate the current breakpoints and aliases.
@sp 1
@item quit [-y]
@kindex quit (mdb command)
Quits the debugger and aborts the execution of the program.
If the option @samp{-y} is not present, asks for confirmation first.
Any answer starting with @samp{y}, or end-of-file, is considered confirmation.
@sp 1
End-of-file on the debugger's input is considered a quit command.
@end table

@c ----------------------------------------------------------------------------

@ifset aditi
@node Using Aditi
@chapter Using Aditi
@cindex Aditi
@cindex database, deductive
@cindex deductive database

The Mercury compiler allows compilation of predicates for execution
using the Aditi2 deductive database system. There are several sources
of useful information:

@itemize @bullet
@item
the ``Aditi deductive database interface'' section of the
``Implementation-dependent extensions'' chapter in the
Mercury Language Reference Manual
@item
the Aditi web site at <http://www.cs.mu.oz.au/aditi>
@item
the documentation supplied with Aditi, especially the file
@file{$ADITI_HOME/doc/aditi.m}
@item
the samples provided with the Aditi distribution in @file{$ADITI_HOME/demos}
@end itemize

As an alternative to compiling stand-alone programs, you can execute
queries using the Aditi query shell.

The Aditi interface library is installed as part of the Aditi
installation process. To use the Aditi library in your programs, use
the Mmakefile in @file{$ADITI_HOME/demos/transactions} as a template.

@end ifset

@c ----------------------------------------------------------------------------

@node Profiling
@chapter Profiling
@pindex mprof
@pindex mdprof
@cindex Profiling
@cindex Profiling memory allocation
@cindex Time profiling
@cindex Heap profiling
@cindex Memory profiling
@cindex Allocation profiling
@cindex Deep profiling

@menu
* Profiling introduction::          What is profiling useful for?
* Building profiled applications::  How to enable profiling.
* Creating profiles::               How to create profile data.
* Using mprof for time profiling::  How to analyze the time performance of a
                                    program with mprof.
* Using mprof for memory profiling::How to analyze the memory performance of a
                                    program with mprof.
* Using mdprof::                    How to analyze the time and/or memory
                                    performance of a program with mdprof.
* Profiling and shared libraries::  Profiling dynamically linked executables.
@end menu

@node Profiling introduction
@section Profiling introduction
@cindex Profiling
@cindex Measuring performance
@cindex Optimization
@cindex Efficiency

To obtain the best trade-off between productivity and efficiency,
programmers should not spend too much time optimizing their code
until they know which parts of the code are really taking up most of the time.
Only once the code has been profiled should the programmer consider
making optimizations that would improve efficiency
at the expense of readability or ease of maintenance.
A good profiler is therefore a tool
that should be part of every software engineer's toolkit.

Mercury programs can be analyzed using two distinct profilers.
The Mercury profiler @samp{mprof} is a conventional call-graph profiler
(or graph profiler for short) in the style of @samp{gprof}.
The Mercury deep profiler @samp{mdprof} is a new kind of profiler
that associates a lot more context with each measurement.
@samp{mprof} can be used to profile either time or space,
but not both at the same time;
@samp{mdprof} can profile both time and space at the same time.

@node Building profiled applications
@section Building profiled applications
@cindex Building profiled applications
@pindex mprof
@pindex mdprof
@cindex Time profiling
@cindex Heap profiling
@cindex Memory profiling
@cindex Allocation profiling
@cindex Deep profiling

To enable profiling, your program must be built with profiling enabled.
The two different profilers require different support,
and thus you must choose which one to enable when you build your program.

@itemize @bullet
@item
To build your program with time profiling enabled for @samp{mprof},
pass the @samp{-p} (@samp{--profiling}) option to @samp{mmc}
(and also to @samp{mgnuc} and @samp{ml}, if you invoke them separately).
@item
To build your program with memory profiling enabled for @samp{mprof},
pass the @samp{--memory-profiling} option to @samp{mmc},
@samp{mgnuc} and @samp{ml}.
@item
To build your program with deep profiling enabled (for @samp{mdprof}),
pass the @samp{--deep-profiling} option to @samp{mmc},
@samp{mgnuc} and @samp{ml}.
@end itemize

If you are using Mmake,
then you pass these options to all the relevant programs
by setting the @samp{GRADEFLAGS} variable in your Mmakefile,
e.g. by adding the line @samp{GRADEFLAGS=--profiling}. 
(For more information about the different grades,
see @ref{Compilation model options}.)

Enabling profiling has several effects.
First, it causes the compiler to generate slightly modified code,
which counts the number of times each predicate or function is called,
and for every call, records the caller and callee.
With deep profiling, there are other modifications as well,
the most important impact of which is the loss of tail-recursion
for groups of mutually tail-recursive predicates
(self-tail-recursive predicates stay tail-recursive).
Second, your program will be linked with versions of the library and runtime
that were compiled with the same kind of profiling enabled.
Third, if you enable graph profiling,
the compiler will generate for each source file
the static call graph for that file in @samp{@var{module}.prof}.

@node Creating profiles
@section Creating profiles
@cindex Profiling
@cindex Creating profiles
@pindex mprof
@pindex mdprof
@cindex Time profiling
@cindex Heap profiling
@cindex Memory profiling
@cindex Allocation profiling
@cindex Deep profiling

Once you have created a profiled executable,
you can gather profiling information by running the profiled executable
on some test data that is representative of the intended uses of the program.
The profiling version of your program
will collect profiling information during execution,
and save this information at the end of execution,
provided execution terminates normally and not via an abort.

Executables compiled with @samp{--profiling}
save profiling data in the files
@file{Prof.Counts}, @file{Prof.Decls}, and @file{Prof.CallPair}.
(@file{Prof.Decl} contains the names
of the procedures and their associated addresses,
@file{Prof.CallPair} records the number of times
each procedure was called by each different caller,
and @file{Prof.Counts} records the number of times
that execution was in each procedure when a profiling interrupt occurred.)
Executables compiled with @samp{--memory-profiling}
will use two of those files (@file{Prof.Decls} and @file{Prof.CallPair})
and a two others: @file{Prof.MemoryWords} and @file{Prof.MemoryCells}.
Executables compiled with @samp{--deep-profiling}
save profiling data in a single file, @file{Deep.data}.

It is also possible to combine @samp{mprof} profiling results
from multiple runs of your program.
You can do by running your program several times,
and typing @samp{mprof_merge_counts} after each run.
It is not (yet) possible to combine @samp{mdprof} profiling results
from multiple runs of your program.

Due to a known timing-related bug in our code,
you may occasionally get segmentation violations
when running your program with @samp{mprof} profiling enabled.
If this happens, just run it again --- the problem occurs only very rarely.
The same vulnerability does not occur with @samp{mdprof} profiling.

With both profilers,
you can control whether time profiling measures
real (elapsed) time, user time plus system time, or user time only,
by including the options @samp{-Tr}, @samp{-Tp}, or @samp{-Tv} respectively
in the environment variable MERCURY_OPTIONS
when you run the program to be profiled.
@c (See the environment variables section below.)
Currently, the @samp{-Tp} and @samp{-Tv} options don't work on Windows,
so on Windows you must explicitly specify @samp{-Tr}.
@c the above sentence is duplicated below

The default is user time plus system time,
which counts all time spent executing the process,
including time spent by the operating system working on behalf of the process,
but not including time that the process was suspended
(e.g. due to time slicing, or while waiting for input).
When measuring real time,
profiling counts even periods during which the process was suspended.
When measuring user time only,
profiling does not count time inside the operating system at all.

@node Using mprof for time profiling
@section Using mprof for time profiling
@pindex mprof
@cindex Time profiling

To display the graph profile information
gathered from one or more profiling runs,
just type @samp{mprof} or @samp{mprof -c}.
(For programs built with @samp{--high-level-code},
you need to also pass the @samp{--no-demangle} option to @samp{mprof} as well.)
@findex --high-level-code
@findex --demangle
@findex --no-demangle
Note that @samp{mprof} can take quite a while to execute
(especially with @samp{-c}),
and will usually produce quite a lot of output,
so you will usually want to redirect the output into a file
with a command such as @samp{mprof > mprof.out}.

The output of @samp{mprof -c} consists of three major sections.
These are named the call graph profile,
the flat profile and the alphabetic listing.
The output of @samp{mprof} contains
the flat profile and the alphabetic listing only.

@cindex Call graph profile
The call graph profile presents the local call graph of each procedure.
For each procedure it shows
the parents (callers) and children (callees) of that procedure,
and shows the execution time and call counts for each parent and child.
It is sorted on the total amount of time spent
in the procedure and all of its descendents
(i.e. all of the procedures that it calls, directly or indirectly.)

@cindex Flat profile
The flat profile presents the just execution time spent in each procedure.
It does not count the time spent in descendents of a procedure.

The alphabetic listing just lists the procedures in alphabetical order,
along with their index number in the call graph profile,
so that you can quickly find the entry for a particular procedure
in the call graph profile.

@cindex Profiling interrupts
The profiler works by interrupting the program at frequent intervals,
and each time recording the currently active procedure and its caller.
It uses these counts to determine
the proportion of the total time spent in each procedure.
This means that the figures calculated for these times
are only a statistical approximation to the real values,
and so they should be treated with some caution.
In particular, if the profiler's assumption
that calls to a procedure from different callers have roughly similar costs
is not true,
the graph profile can be quite misleading.

The time spent in a procedure and its descendents is calculated by
propagating the times up the call graph,
assuming that each call to a procedure from a particular caller
takes the same amount of time.
This assumption is usually reasonable,
but again the results should be treated with caution.
(The deep profiler does not make such an assumption,
and hence its output is significantly more reliable.)

@cindex Garbage collection, profiling
Note that any time spent in a C function
(e.g. time spent in @samp{GC_malloc()},
which does memory allocation and garbage collection)
is credited to the Mercury procedure that called that C function.

Here is a small portion of the call graph profile from an example program.

@example
                                  called/total       parents
index  %time    self descendents  called+self    name           index
                                  called/total       children

                                                     <spontaneous>
[1]    100.0    0.00        0.75       0         call_engine_label [1]
                0.00        0.75       1/1           do_interpreter [3]

-----------------------------------------------

                0.00        0.75       1/1           do_interpreter [3]
[2]    100.0    0.00        0.75       1         io__run/0(0) [2]
                0.00        0.00       1/1           io__init_state/2(0) [11]
                0.00        0.74       1/1           main/2(0) [4]

-----------------------------------------------

                0.00        0.75       1/1           call_engine_label [1]
[3]    100.0    0.00        0.75       1         do_interpreter [3]
                0.00        0.75       1/1           io__run/0(0) [2]

-----------------------------------------------

                0.00        0.74       1/1           io__run/0(0) [2]
[4]     99.9    0.00        0.74       1         main/2(0) [4]
                0.00        0.74       1/1           sort/2(0) [5]
                0.00        0.00       1/1           print_list/3(0) [16]
                0.00        0.00       1/10          io__write_string/3(0) [18]

-----------------------------------------------

                0.00        0.74       1/1           main/2(0) [4]
[5]     99.9    0.00        0.74       1         sort/2(0) [5]
                0.05        0.65       1/1           list__perm/2(0) [6]
                0.00        0.09   40320/40320       sorted/1(0) [10]

-----------------------------------------------

                                       8             list__perm/2(0) [6]
                0.05        0.65       1/1           sort/2(0) [5]
[6]     86.6    0.05        0.65       1+8      list__perm/2(0) [6]
                0.00        0.60    5914/5914        list__insert/3(2) [7]
                                       8             list__perm/2(0) [6]

-----------------------------------------------

                0.00        0.60    5914/5914        list__perm/2(0) [6]
[7]     80.0    0.00        0.60    5914         list__insert/3(2) [7]
                0.60        0.60    5914/5914        list__delete/3(3) [8]

-----------------------------------------------

                                   40319             list__delete/3(3) [8]
                0.60        0.60    5914/5914        list__insert/3(2) [7]
[8]     80.0    0.60        0.60    5914+40319  list__delete/3(3) [8]
                                   40319             list__delete/3(3) [8]

-----------------------------------------------

                0.00        0.00       3/69283       tree234__set/4(0) [15]
                0.09        0.09   69280/69283       sorted/1(0) [10]
[9]     13.3    0.10        0.10   69283         compare/3(0) [9]
                0.00        0.00       3/3           __Compare___io__stream/0(0) [20]
                0.00        0.00   69280/69280       builtin_compare_int/3(0) [27]

-----------------------------------------------

                0.00        0.09   40320/40320       sort/2(0) [5]
[10]    13.3    0.00        0.09   40320         sorted/1(0) [10]
                0.09        0.09   69280/69283       compare/3(0) [9]

-----------------------------------------------
@end example

The first entry is @samp{call_engine_label} and its parent is
@samp{<spontaneous>}, meaning that it is the root of the call graph.
(The first three entries, @samp{call_engine_label}, @samp{do_interpreter},
and @samp{io__run/0} are all part of the Mercury runtime;
@samp{main/2} is the entry point to the user's program.)

Each entry of the call graph profile consists of three sections, the parent
procedures, the current procedure and the children procedures.

Reading across from the left, for the current procedure the fields are:

@itemize @bullet
@item
The unique index number for the current procedure.
(The index numbers are used only to make it easier to find
a particular entry in the call graph.)

@item
The percentage of total execution time spent in the current procedure
and all its descendents.
As noted above, this is only a statistical approximation.

@item
The ``self'' time: the time spent executing code that is
part of current procedure.
As noted above, this is only a statistical approximation.

@item
The descendent time: the time spent in the
current procedure and all its descendents.
As noted above, this is only a statistical approximation.

@item
The number of times a procedure is called.
If a procedure is (directly) recursive, this column
will contain the number of calls from other procedures,
a plus sign, and then the number of recursive calls.
These numbers are exact, not approximate.

@item
The name of the procedure followed by its index number.
@end itemize

The predicate or function names are not just followed by their arity but
also by their mode in brackets.  A mode of zero corresponds to the first mode
declaration of that predicate in the source code.  For example,
@samp{list__delete/3(3)} corresponds to the @samp{(out, out, in)} mode
of @samp{list__delete/3}.

Now for the parent and child procedures the self and descendent time have
slightly different meanings.  For the parent procedures the self and descendent
time represent the proportion of the current procedure's self and descendent
time due to that parent.  These times are obtained using the assumption that
each call contributes equally to the total time of the current procedure.

@node Using mprof for memory profiling
@section Using mprof for memory profiling
@pindex mprof
@cindex Memory profiling
@cindex Allocation profiling
@cindex Heap profiling
@cindex Profiling memory allocation

To create a memory profile, you can invoke @samp{mprof}
with the @samp{-m} (@samp{--profile memory-words}) option.
This will profile the amount of memory allocated, measured in units of words. 
(A word is 4 bytes on a 32-bit architecture,
and 8 bytes on a 64-bit architecture.)

Alternatively, you can use @samp{mprof}'s @samp{-M}
(@samp{--profile memory-cells}) option.
This will profile memory in units of ``cells''.
A cell is a group of words allocated together in a single allocation,
to hold a single object.
Selecting this option this will therefore profile
the number of memory allocations,
while ignoring the size of each memory allocation.

With memory profiling, just as with time profiling,
you can use the @samp{-c} (@samp{--call-graph}) option to display
call graph profiles in addition to flat profiles.

Note that Mercury's memory profiler will only tell you about allocation,
not about deallocation (garbage collection).
It can tell you how much memory was allocated by each procedure,
but it won't tell you how long the memory was live for,
or how much of that memory was garbage-collected.
This is also true for @samp{mdprof}.

@node Using mdprof
@section Using mdprof
@pindex mdprof
@cindex Deep profiling

To display the information contained in a deep profiling data file
(which will be called @file{Deep.data} unless you renamed it),
start up your browser and give it a URL of the form
@file{http://server.domain.name/cgi-bin/mdprof?/full/path/name/Deep.data}.
The @file{server.domain.name} part should be the name of a machine
with the following qualifications:
it should have a web server running on it,
and it should have the @samp{mdprof} program installed
in its @file{/usr/lib/cgi-bin} directory.
The @file{/full/path/name/Deep.data} part
should be the full path name of the deep profiling data file
whose data you wish to explore.
The name of this file must not have dollar signs in it.

@node Profiling and shared libraries
@section Profiling and shared libraries
@pindex mprof
@cindex Shared libraries and profiling
@cindex Profiling and shared libraries
@vindex LD_BIND_NOW

On some operating systems,
Mercury's profiling doesn't work properly with shared libraries.
The symptom is errors ("map__lookup failed") or warnings from @samp{mprof}.
On some systems, the problem occurs because the C implementation
fails to conform to the semantics specified by the ISO C standard
for programs that use shared libraries.
For other systems, we have not been able to analyze the cause of the failure
(but we suspect that the cause may be the same as on those systems
where we have been able to analyze it).

If you get errors or warnings from @samp{mprof},
and your program is dynamically linked,
try rebuilding your application statically linked,
e.g. by using @samp{MLFLAGS=--static} in your Mmakefile.
Another work-around that sometimes works is to set the environment variable
@samp{LD_BIND_NOW} to a non-null value before running the program.

@c ----------------------------------------------------------------------------

@node Invocation
@chapter Invocation

This section contains a brief description of all the options
available for @samp{mmc}, the Mercury compiler.
Sometimes this list is a little out-of-date;
use @samp{mmc --help} to get the most up-to-date list.
@findex --help

@menu
* Invocation overview::
* Verbosity options::
* Warning options::
* Output options::
* Auxiliary output options::
* Language semantics options::
* Termination analysis options::
* Compilation model options::
* Code generation options::
* Optimization options::
* Target code compilation options::
* Link options::
* Build system options::
* Miscellaneous options::
@end menu

@node Invocation overview
@section Invocation overview

@code{mmc} is invoked as
@example
mmc [@var{options}] @var{arguments}
@end example

Arguments can be either module names or file names.
Arguments ending in @samp{.m} are assumed to be file names,
while other arguments are assumed to be module names, with
@samp{.} (rather than @samp{__} or @samp{:}) as module qualifier.
If you specify a module name such as @samp{foo.bar.baz},
the compiler will look for the source in files @file{foo.bar.baz.m},
@file{bar.baz.m}, and @file{baz.m}, in that order.

Options are either short (single-letter) options preceded by a single @samp{-},
or long options preceded by @samp{--}.
Options are case-sensitive.
We call options that do not take arguments @dfn{flags}.
Single-letter flags may be grouped with a single @samp{-}, e.g. @samp{-vVc}.
Single-letter flags may be negated
by appending another trailing @samp{-}, e.g. @samp{-v-}.
Long flags may be negated by preceding them with @samp{no-},
e.g. @samp{--no-verbose}.
@findex --no-

@node Warning options
@section Warning options
@cindex Warning options
@table @code
@item -w
@itemx --inhibit-warnings
@findex -w
@findex --inhibit-warnings
Disable all warning messages.

@sp 1
@item --halt-at-warn
@findex --halt-at-warn
This option causes the compiler to treat all
warnings as if they were errors.  This means that
if any warning is issued, the compiler will not
generate code --- instead, it will return a
non-zero exit status.

@sp 1
@item --halt-at-syntax-error
@findex --halt-at-syntax-error
This option causes the compiler to halt immediately
after syntax checking and not do any semantic checking
if it finds any syntax errors in the program.

@sp 1
@item --inhibit-accumulator-warnings
@findex --inhibit-accumulator-warnings
Don't warn about argument order rearrangement caused by
@samp{--introduce-accumulators}.

@sp 1
@item --no-warn-singleton-variables
@findex --no-warn-singleton-variables
@findex --warn-singleton-variables
Don't warn about variables which only occur once.

@sp 1
@item --no-warn-missing-det-decls
@findex --no-warn-missing-det-decls
@findex --warn-missing-det-decls
For predicates that are local to a module (those that
are not exported), don't issue a warning if the @samp{pred}
or @samp{mode} declaration does not have a determinism annotation.
Use this option if you want the compiler to perform automatic
determinism inference for non-exported predicates.

@sp 1
@item --no-warn-det-decls-too-lax
@findex --no-warn-det-decls-too-lax
@findex --warn-det-decls-too-lax
Don't warn about determinism declarations
which could have been stricter.

@sp 1
@item --no-warn-inferred-erroneous
@findex --no-warn-inferred-erroneous
@findex --warn-inferred-erroneous
Don't warn about procedures whose determinism is inferred erroneous
but whose determinism declarations are laxer.

@sp 1
@item --no-warn-nothing-exported
@findex --no-warn-nothing-exported
@findex --warn-nothing-exported
Don't warn about modules whose interface sections have no
exported predicates, functions, insts, modes or types.

@sp 1
@item --warn-unused-args
@findex --warn-unused-args
Warn about predicate or function arguments which are not used.

@sp 1
@item --warn-interface-imports
@findex --warn-interface-imports
Warn about modules imported in the interface which are not
used in the interface.

@sp 1
@item --warn-missing-opt-files
@findex --warn-missing-opt-files
Warn about @samp{.opt} files that cannot be opened.

@sp 1
@item --warn-missing-trans-opt-files
@findex --warn-missing-trans-opt-files
Warn about @samp{.trans_opt} files that cannot be opened.

@sp 1
@item --warn-non-stratification
@findex --warn-non-stratification
Warn about possible non-stratification of the predicates/functions in the
module.
Non-stratification occurs when a predicate/function can call itself
negatively through some path along its call graph.

@sp 1
@item --no-warn-simple-code
@findex --no-warn-simple-code
@findex --warn-simple-code
Disable warnings about constructs which are so
simple that they are likely to be programming errors.

@sp 1
@item --warn-duplicate-calls
@findex --warn-duplicate-calls
Warn about multiple calls to a predicate with the same
input arguments.

@sp 1
@item --no-warn-missing-module-name
@findex --no-warn-missing-module-name
@findex --warn-missing-module-name
Disable warnings for modules that do not start with a
@samp{:- module} declaration.

@sp 1
@item --no-warn-wrong-module-name
@findex --no-warn-wrong-module-name
@findex --warn-wrong-module-name
Disable warnings for modules whose @samp{:- module} declaration
does not match the module's file name.

@sp 1
@item --no-warn-smart-recompilation
@findex --warn-smart-recompilation
@findex --no-warn-smart-recompilation
Disable warnings from the smart recompilation system.

@sp 1
@item --no-warn-undefined-options-variables
@findex --no-warn-undefined-options-variables
@findex --make
Warn about references to undefined variables in
options files with @samp{--make}.

@sp 1
@item --warn-non-tail-recursion
@findex --warn-non-tail-recursion
Warn about any directly recursive calls that are not tail recursive.
This option also requires @samp{--high-level-code}.
@end table

@node Verbosity options
@section Verbosity options
@cindex Verbosity options
@table @code
@item -v
@itemx --verbose
@findex -v
@findex --verbose
Output progress messages at each stage in the compilation.

@sp 1
@item -V
@itemx --very-verbose
@findex -V
@findex --very-verbose
Output very verbose progress messages.

@sp 1
@item -E
@itemx --verbose-error-messages
@findex -E
@findex --verbose-error-messages
Explain error messages.  Asks the compiler to give you a more
detailed explanation of any errors it finds in your program.

@sp 1
@item --no-verbose-make
@findex --no-verbose-make
@findex --make
Disable messages about the progress of builds using
the @samp{--make} option.

@sp 1
@item --output-compile-error-lines @var{n}
@findex --output-compile-error-lines
@findex --make
With @samp{--make}, output the first @var{n} lines of the @samp{.err}
file after compiling a module (default: 15).

@sp 1
@item --verbose-commands
@findex --verbose-commands
Output each external command before it is run.
Note that some commands will only be printed
with @samp{--verbose}.

@sp 1
@item --verbose-recompilation
@findex --verbose-recompilation
When using @samp{--smart-recompilation}, output messages
explaining why a module needs to be recompiled.

@sp 1
@item --find-all-recompilation-reasons
@findex --find-all-recompilation-reasons
Find all the reasons why a module needs to be recompiled,
not just the first.  Implies @samp{--verbose-recompilation}.

@sp 1
@item -S
@itemx --statistics
@findex -S
@findex --statistics
Output messages about the compiler's time/space usage.
At the moment this option implies @samp{--no-trad-passes},
so you get information at the boundaries between phases of the compiler.
@findex --no-trad-passes
@findex --trad-passes

@sp 1
@item -T
@itemx --debug-types
@findex -T
@findex --debug-types
Output detailed debugging traces of the type checking.

@sp 1
@item -N
@itemx --debug-modes
@findex -N
@findex --debug-modes
Output detailed debugging traces of the mode checking.

@sp 1
@item --debug-det
@itemx --debug-determinism
@findex --debug-det
@findex --debug-determinism
Output detailed debugging traces of determinism analysis.

@sp 1
@item --debug-opt
@findex --debug-opt
Output detailed debugging traces of the optimization process.

@sp 1
@item --debug-pd
@findex --debug-pd
Output detailed debugging traces of the partial
deduction and deforestation process.

@ifset aditi
@sp 1
@item --debug-rl-gen
@findex --debug-rl-gen
Output detailed debugging traces of Aditi-RL code generation
(@pxref{Using Aditi}).

@sp 1
@item --debug-rl-opt
@findex --debug-rl-opt
Output detailed debugging traces of Aditi-RL optimization
(@pxref{Using Aditi}).
@end ifset
@c aditi

@sp 1
@item --debug-liveness <n>
@findex --debug-liveness
Output detailed debugging traces of the liveness analysis
of the predicate with the given predicate id.

@sp 1
@item --debug-make
@findex --debug-make
@findex --make
Output detailed debugging traces of the `--make' option.

@end table

@node Output options
@section Output options
These options are mutually exclusive.
If more than one of these options is specified, only the first in
this list will apply.
If none of these options are specified, the default action is to
compile and link the modules named on the command line to produce
an executable.

@table @code
@item -f
@itemx --generate-source-file-mapping
@findex --generate-source-file-mapping
Output the module name to file name mapping for the list
of source files given as non-option arguments to mmc
to @file{Mercury.modules}. This must be done before
@samp{mmc --generate-dependencies} if there are any modules
for which the file name does not match the module name.
If there are no such modules the mapping need not be
generated.

@item -M
@itemx --generate-dependencies
@findex -M
@findex --generate-dependencies
@cindex dependencies
Output ``Make''-style dependencies for the module and all of its
dependencies to @file{@var{module}.dep}, @file{@var{module}.dv} and the
relevant @samp{.d} files.

@item --generate-module-order
Output the strongly connected components of the module
dependency graph in top-down order to @file{@var{module}.order}.
Implies @samp{--generate-dependencies}.

@item --generate-mmc-deps
@itemx --generate-mmc-make-module-dependencies
@findex --generate-mmc-deps
@findex --generate-mmc-make-module-dependencies
@findex --make
Generate dependencies for use by @samp{mmc --make} even
when using Mmake. This is recommended when building a
library for installation.

@sp 1
@item -i
@itemx --make-int
@itemx --make-interface
@findex -i
@findex --make-int
@findex --make-interface
Write the module interface to @file{@var{module}.int}.
Also write the short interface to @file{@var{module}.int2}.

@sp 1
@item --make-short-int
@itemx --make-short-interface
@findex --make-short-int
@findex --make-short-interface
Write the unqualified version of the short interface to
@file{@var{module}.int3}.

@sp 1
@item --make-priv-int
@itemx --make-private-interface
@findex --make-priv-int
@findex --make-private-interface
Write the module's private interface (used for compiling
nested sub-modules) to @file{@var{module}.int0}.

@sp 1
@item --make-opt-int
@itemx --make-optimization-interface
@findex --make-opt-int
@findex --make-optimization-interface
Write information used for inter-module optimization to
@file{@var{module}.opt}.

@sp 1
@item --make-trans-opt
@itemx --make-transitive-optimization-interface
@findex --make-trans-opt
@findex --make-transitive-optimization-interface
Write the @file{@var{module}.trans_opt} file.  This file is used to store
information used for inter-module optimization.  The information is read 
in when the compiler is invoked with the
@samp{--transitive-intermodule-optimization} option. 
The file is called the ``transitive'' optimization interface file
because a @samp{.trans_opt} file may depend on other 
@samp{.trans_opt} and @samp{.opt} files.  In contrast,
a @samp{.opt} file can only hold information derived directly
from the corresponding @samp{.m} file.

@sp 1
@item -P
@itemx --pretty-print
@itemx --convert-to-mercury
@findex -P
@findex --pretty-print
@findex --convert-to-mercury
Convert to Mercury.  Output to file @file{@var{module}.ugly}.
This option acts as a Mercury ugly-printer.
(It would be a pretty-printer, except that comments are stripped
and nested if-then-elses are indented too much --- so the result
is rather ugly.)

@sp 1
@item --typecheck-only
@findex --typecheck-only
Just check the syntax and type-correctness of the code.
Don't invoke the mode analysis and later passes of the compiler.
When converting Prolog code to Mercury,
it can sometimes be useful to get the types right first
and worry about modes second;
this option supports that approach.

@sp 1
@item -e
@itemx --errorcheck-only
@findex -e
@findex --errorcheck-only
Check the module for errors, but do not generate any code.

@sp 1
@item -C
@itemx --target-code-only
@findex -C
@findex --target-code-only
Generate target code (i.e. C in @file{@var{module}.c},
assembler in @file{@var{module}.s} or @file{@var{module}.pic_s},
IL in @file{@var{module}.il} or Java in @file{@var{module}.java}),
but not object code.

@sp 1
@item -c
@itemx --compile-only
@findex -c
@findex --compile-only
Generate C code in @file{@var{module}.c}
and object code in @file{@var{module}.o}
but do not attempt to link the named modules.

@ifset aditi
@sp 1
@item --aditi-only
@findex --aditi-only
Write Aditi-RL bytecode to @file{@var{module}.rlo} and do not compile to C
(@pxref{Using Aditi}).
@end ifset
@c aditi

@sp 1
@item --output-grade-string
@findex --output-grade-string
Compute from the rest of the option settings the canonical grade
string and print it on the standard output.
@end table

@node Auxiliary output options
@section Auxiliary output options
@table @code
@item --smart-recompilation
@findex --smart-recompilation
When compiling, write program dependency information
to be used to avoid unnecessary recompilations if an
imported module's interface changes in a way which does
not invalidate the compiled code. @samp{--smart-recompilation} does
not yet work with @samp{--intermodule-optimization}.

@item --no-assume-gmake
@findex --no-assume-gmake
@findex --assume-gmake
When generating @file{.d}, @file{.dep} and @file{.dv} files,
generate Makefile fragments that use only the features of standard make;
do not assume the availability of GNU Make extensions.
This can make these files significantly larger.

@item --trace-level @var{level}
@findex --trace-level @var{level}
Generate code that includes the specified level of execution tracing.
The @var{level} should be one of
@samp{none}, @samp{shallow}, @samp{deep}, and @samp{default}.
See @ref{Debugging}.

@item --trace-optimized
@findex --trace-optimized
Do not disable optimizations that can change the trace.

@item --no-delay-death
@findex --no-delay-death
@findex --delay-death
When the trace level is `deep', the compiler normally
preserves the values of variables as long as possible, even
beyond the point of their last use, in order to make them
accessible from as many debugger events as possible.
However, it will not do this if this option is given.

@item --stack-trace-higher-order
@findex --stack-trace-higher-order
Enable stack traces through predicates and functions with
higher-order arguments, even if stack tracing is not
supported in general.

@item --generate-bytecode
@findex --generate-bytecode
@c Output a bytecode version of the module
@c into the @file{@var{module}.bytecode} file,
@c and a human-readable version of the bytecode
@c into the @file{@var{module}.bytedebug} file.
@c The bytecode is for an experimental debugger.
Output a bytecode form of the module for use
by an experimental debugger.

@item --auto-comments
@findex --auto-comments
Output comments in the @file{@var{module}.c} file.
This is primarily useful for trying to understand
how the generated C code relates to the source code,
e.g. in order to debug the compiler.
The code may be easier to understand if you also use the
@samp{--no-llds-optimize} option.
@findex --no-llds-optimize
@findex --llds-optimize

@sp 1
@item -n-
@itemx --no-line-numbers
@findex -n-
@findex --no-line-numbers
@findex --line-numbers
Do not put source line numbers in the generated code.
The generated code may be in C (the usual case)
or in Mercury (with @samp{--convert-to-mercury}).

@sp 1
@item --show-dependency-graph
@findex --show-dependency-graph
Write out the dependency graph to @var{module}.dependency_graph.

@sp 1
@item -d @var{stage}
@itemx --dump-hlds @var{stage}
@findex -d
@findex --dump-hlds
Dump the HLDS (a high-level intermediate representation) after
the specified stage number or stage name to
@file{@var{module}.hlds_dump.@var{num}-@var{name}}.
Stage numbers range from 1 to 99; not all stage numbers are valid.
The special stage name @samp{all} causes the dumping of all stages.
Multiple dump options accumulate.

@sp 1
@item --dump-hlds-options @var{options}
@findex --dump-hlds-options
With @samp{--dump-hlds}, include extra detail in the dump.
Each type of detail is included in the dump
if its corresponding letter occurs in the option argument.
These details are:
a - argument modes in unifications,
b - builtin flags on calls,
c - contexts of goals and types,
d - determinism of goals,
f - follow_vars sets of goals,
g - goal feature lists,
i - instmap deltas of goals,
l - pred/mode ids and unify contexts of called predicates,
m - mode information about clauses,
n - nonlocal variables of goals,
p - pre-birth, post-birth, pre-death and post-death sets of goals,
r - resume points of goals,
s - store maps of goals,
t - results of termination analysis,
u - unification categories,
v - variable numbers in variable names,
A - argument passing information,
C - clause information,
G - compile-time garbage collection information,
I - imported predicates,
M - mode and inst information,
P - path information,
T - type and typeclass information,
U - unify and compare predicates.

@sp 1
@item --dump-mlds @var{stage}
@findex --dump-mlds
Dump the MLDS (a C-like intermediate representation) after
the specified stage number or stage name.
The MLDS is converted to a C source file/header file pair,
which is dumped to @file{@var{module}.c_dump.@var{num}-@var{name}}
and @file{@var{module}.h_dump.@var{num}-@var{name}}.
Stage numbers range from 1 to 99; not all stage numbers are valid.
The special stage name @samp{all} causes the dumping of all stages.
Multiple dump options accumulate.

@sp 1
@item --verbose-dump-mlds @var{stage}
@findex --verbose-dump-mlds
Dump the internal compiler representation of the MLDS,
after the specified stage number or stage name, to
@file{@var{module}.mlds_dump.@var{num}-@var{name}}.

@ifset aditi
@sp 1
@item --dump-rl
@findex --dump-rl
Output a human readable form of the internal compiler representation
of the generated Aditi-RL code to @file{@var{module}.rl_dump}
(@pxref{Using Aditi}).

@sp 1
@item --dump-rl-bytecode
@findex --dump-rl-bytecode
Output a human readable representation of the generated Aditi-RL
bytecodes @file{@var{module}.rla}. Aditi-RL bytecodes are directly
executed by the Aditi system (@pxref{Using Aditi}).

@sp 1
@item --generate-schemas
@findex --generate-schemas
Output schema strings for Aditi base relations to
@file{@var{module}.base_schema} and for Aditi derived
relations to @file{@var{module}.derived_schema}. A schema
string is a representation of the types of the attributes
of a relation (@pxref{Using Aditi}).

@end ifset
@c aditi

@end table

@node Language semantics options
@section Language semantics options
@cindex Language semantics options
@cindex Semantics options
@cindex Order of execution
@cindex Reordering
@cindex Optimization

See the Mercury language reference manual for detailed explanations
of these options.

@table @code
@item --no-reorder-conj
@findex --no-reorder-conj
@findex --reorder-conj
Execute conjunctions left-to-right except where the modes imply
that reordering is unavoidable.

@sp 1
@item --no-reorder-disj
@findex --no-reorder-disj
@findex --reorder-disj
Execute disjunctions strictly left-to-right.

@sp 1
@item --fully-strict
@findex --fully-strict
Don't optimize away loops or calls to @code{error/1}.

@sp 1
@item --infer-all
@findex --infer-all
@cindex Inference
An abbreviation for @samp{--infer-types --infer-modes --infer-det}.

@sp 1
@item --infer-types
@findex --infer-types
@cindex Inference of types
If there is no type declaration for a predicate or function,
try to infer the type, rather than just reporting an error.

@sp 1
@item --infer-modes
@findex --infer-modes
@cindex Inference of modes
If there is no mode declaration for a predicate,
try to infer the modes, rather than just reporting an error.

@sp 1
@item --no-infer-det
@itemx --no-infer-determinism
@findex --no-infer-det
@findex --no-infer-determinism
@findex --infer-det
@findex --infer-determinism
@cindex Determinism inference
@cindex Inference of determinism
If there is no determinism declaration for a procedure,
don't try to infer the determinism, just report an error.

@sp 1
@item --type-inference-iteration-limit @var{n}
@findex --type-inference-iteration-limit
@cindex Inference of types
@cindex Type inference
Perform at most @var{n} passes of type inference (default: 60).

@sp 1
@item --mode-inference-iteration-limit @var{n}
@cindex Inference of modes
@cindex Mode inference
Perform at most @var{n} passes of mode inference (default: 30).
@end table

@node Termination analysis options
@section Termination analysis options
@cindex Termination analysis options

For detailed explanations, see the ``Termination analysis'' section
of the ``Implementation-dependent extensions'' chapter in the Mercury
Language Reference Manual.

@table @code
@item --enable-term
@itemx --enable-termination
@findex --enable-term
@findex --enable-termination
Enable termination analysis.  Termination analysis analyses each mode of
each predicate to see whether it terminates.  The @samp{terminates},
@samp{does_not_terminate} and @samp{check_termination}
pragmas have no effect unless termination analysis is enabled.  When
using termination, @samp{--intermodule-optimization} should be enabled,
as it greatly improves the accuracy of the analysis.

@sp 1
@item --chk-term
@itemx --check-term
@itemx --check-termination
@findex --chk-term
@findex --check-term
@findex --check-termination
Enable termination analysis, and emit warnings for some predicates or
functions that cannot be proved to terminate.  In many cases in which the
compiler is unable to prove termination, the problem is either a lack of
information about the termination properties of other predicates, or the
fact that the program used language constructs (such as higher order
calls) which cannot be analysed.  In these cases the compiler does
not emit a warning of non-termination, as it is likely to be spurious.

@sp 1
@item --verb-chk-term
@itemx --verb-check-term
@itemx --verbose-check-termination
@findex --verb-chk-term
@findex --verb-check-term
@findex --verbose-check-termination
Enable termination analysis, and emit warnings for all predicates or
functions that cannot be proved to terminate.

@sp 1
@item --term-single-arg @var{limit}
@itemx --termination-single-argument-analysis @var{limit}
@findex --term-single-arg @var{limit}
@findex --termination-single-argument-analysis
When performing termination analysis, try analyzing
recursion on single arguments in strongly connected
components of the call graph that have up to @var{limit} procedures.
Setting this limit to zero disables single argument analysis.

@sp 1
@item --termination-norm @var{norm}
@findex --termination-norm
The norm defines how termination analysis measures the size
of a memory cell.  The @samp{simple} norm says that size is always one.
The @samp{total} norm says that it is the number of words in the cell.
The @samp{num-data-elems} norm says that it is the number of words in
the cell that contain something other than pointers to cells of
the same type.

@sp 1
@item --term-err-limit @var{limit}
@itemx --termination-error-limit @var{limit}
@findex --term-err-limit
@findex --termination-error-limit
Print at most @var{n} reasons for any single termination error.

@sp 1
@item --term-path-limit @var{limit}
@itemx --termination-path-limit @var{limit}
@findex --term-path-limit
@findex --termination-path-limit
Perform termination analysis only on predicates with at most @var{n} paths.

@end table

@node Compilation model options
@section Compilation model options
@cindex Link errors
@cindex Undefined symbol
@cindex Compilation model options
@cindex Compilation models
@cindex Compilation grades
@cindex Grades
@cindex ABI (Application Binary Interface)
@cindex Application Binary Interface (ABI)

The following compilation options affect the generated
code in such a way that the entire program must be
compiled with the same setting of these options,
and it must be linked to a version of the Mercury
library which has been compiled with the same setting.
(Attempting to link object files compiled with different
settings of these options will generally result in an error at
link time, typically of the form @samp{undefined symbol MR_grade_@dots{}}
or @samp{symbol MR_runtime_grade multiply defined}.)

The options below must be passed to @samp{mgnuc}, @samp{c2init}
and @samp{ml} as well as to @samp{mmc}. 
If you are using Mmake, then you should specify
these options in the @samp{GRADEFLAGS} variable rather than specifying
them in @samp{MCFLAGS}, @samp{MGNUCFLAGS} and @samp{MLFLAGS}.
@vindex GRADEFLAGS
@vindex MCFLAGS
@vindex MGNUCFLAGS
@vindex MLFLAGS

@menu
* Grades and grade components::                 Setting the compilation model
* Target options::                              Choosing a target language
* Optional features compilation model options:: Debugging, Profiling, etc.
* LLDS back-end compilation model options::     For the original back-end
* MLDS back-end compilation model options::     For the new high-level back-end
* Developer compilation model options::         Not for general use
@end menu

@node Grades and grade components
@subsection Grades and grade components
@cindex Grades and grade components

@table @asis
@item @code{-s @var{grade}}
@itemx @code{--grade @var{grade}}
@findex -s
@findex --grade
Select the compilation model.
The @var{grade} should be a @samp{.} separated list of the
grade options to set. The grade options may be given in any order.
The available options each belong to a set of mutually
exclusive alternatives governing a single aspect of the compilation model.
The set of aspects and their alternatives are:

@cindex none (compilation grade)
@cindex reg (compilation grade)
@cindex jump (compilation grade)
@cindex asm_jump (compilation grade)
@cindex fast (compilation grade)
@cindex asm_fast (compilation grade)
@cindex hlc (compilation grade)
@cindex ilc (compilation grade)
@cindex java (compilation grade)
@cindex .prof (grade modifier)
@cindex .memprof (grade modifier)
@cindex .profdeep (grade modifier)
@cindex .tr (grade modifier)
@cindex .gc (grade modifier)
@cindex .agc (grade modifier)
@cindex .rt (grade modifier)
@cindex .debug (grade modifier)
@cindex .par (grade modifier)
@cindex prof (grade modifier)
@cindex memprof (grade modifier)
@cindex profdeep (grade modifier)
@cindex tr (grade modifier)
@cindex gc (grade modifier)
@cindex agc (grade modifier)
@cindex rt (grade modifier)
@cindex debug (grade modifier)
@cindex par (grade modifier)
@table @asis
@item What target language to use, and (for C) what combination of GNU C extensions to use:
@samp{none}, @samp{reg}, @samp{jump}, @samp{asm_jump},
@samp{fast}, @samp{asm_fast}, @samp{hlc}, @samp{ilc} and @samp{java}
(the default is system dependent).

@item What garbage collection strategy to use:
@samp{gc}, and @samp{agc} (the default is no garbage collection).

@item What kind of profiling to use:
@samp{prof},
@c @samp{proftime}, @samp{profcalls},
and @samp{memprof}
(the default is no profiling).

@item Whether to enable the trail:
@samp{tr} (the default is no trailing).

@item Whether or not to reserve a tag in the data representation of the generated code:
@samp{rt} (the default is no reserved tag)

@item What debugging features to enable:
@samp{debug} (the default is no debugging features).

@item Whether to use a thread-safe version of the runtime environment:
@samp{par} (the default is a non-thread-safe environment).

@end table

The default grade is system-dependent; it is chosen at installation time
by @samp{configure}, the auto-configuration script, but can be overridden
with the environment variable @samp{MERCURY_DEFAULT_GRADE} if desired.
@vindex MERCURY_DEFAULT_GRADE
Depending on your particular installation, only a subset
of these possible grades will have been installed.
Attempting to use a grade which has not been installed
will result in an error at link time.
(The error message will typically be something like
@samp{ld: can't find library for -lmercury}.)

The tables below show the options that are selected by each base grade
and grade modifier; they are followed by descriptions of those options.

@table @asis
@item @var{Grade}
@var{Options implied}.
@findex --gcc-global-registers
@findex --no-gcc-global-registers
@findex --gcc-nonlocal-gotos
@findex --no-gcc-nonlocal-gotos
@findex --asm-labels
@findex --no-asm-labels
@findex --high-level-code
@findex --no-high-level-code
@findex --target
@findex --il
@findex --java
@findex --gc
@findex --profiling
@findex --memory-profiling
@findex --deep-profiling

@item @samp{none}
@code{--target c --no-gcc-global-registers --no-gcc-nonlocal-gotos --no-asm-labels}.

@item @samp{reg}
@code{--target c --gcc-global-registers --no-gcc-nonlocal-gotos --no-asm-labels}.

@item @samp{jump}
@code{--target c --no-gcc-global-registers --gcc-nonlocal-gotos --no-asm-labels}.

@item @samp{fast}
@code{--target c --gcc-global-registers --gcc-nonlocal-gotos --no-asm-labels}.

@item @samp{asm_jump}
@code{--target c --no-gcc-global-registers --gcc-nonlocal-gotos --asm-labels}.

@item @samp{asm_fast}
@code{--target c --gcc-global-registers --gcc-nonlocal-gotos --asm-labels}.

@item @samp{hlc}
@code{--target c --high-level-code}.

@item @samp{ilc}
@code{--target il --high-level-code}.

@item @samp{java}
@code{--target java --high-level-code}.

@item @samp{.gc}
@code{--gc conservative}.

@item @samp{.agc}
@code{--gc accurate}.

@item @samp{.prof}
@code{--profiling}.

@item @samp{.memprof}
@code{--memory-profiling}.

@item @samp{.profdeep}
@code{--deep-profiling}.

@c The following are undocumented because
@c they are basically useless... documenting
@c them would just confuse people.
@c
@c @item @samp{.profall}
@c @code{--profile-calls --profile-time --profile-memory}.
@c (not recommended because --profile-memory interferes with
@c --profile-time)
@c 
@c @item @samp{.proftime}
@c @code{--profile-time}.
@c 
@c @item @samp{.profcalls}
@c @code{--profile-calls}.
@c 
@item @samp{.tr}
@code{--use-trail}.

@item @samp{.rt}
@code{--reserve-tag}.

@item @samp{.debug}
@code{--debug}.

@end table

@end table

@node Target options
@subsection Target options
@cindex Target options

@table @asis
@item @code{--target c} (grades: none, reg, jump, fast, asm_jump, asm_fast, hlc)
@item @code{--target asm} (grades: hlc)
@itemx @code{--il}, @code{--target il} (grades: ilc)
@itemx @code{--java}, @code{--target java} (grades: java)
Specify the target language used for compilation: C, assembler, IL or Java.
C means ANSI/ISO C, optionally with GNU C extensions (see below).
IL means the Microsoft .NET Intermediate Language.
Targets other than C imply @samp{--high-level-code}.

@sp 1
@item @code{--il-only}
@findex --il-only
An abbreviation for @samp{--target il --target-code-only}.
Generate IL assembler code in @file{@var{module}.il}, but do not invoke
ilasm to produce IL object code.

@sp 1
@item --dotnet-library-version @var{version-number}
@findex --dotnet-library-version
The version number for the mscorlib assembly distributed with the
Microsoft .NET SDK.

@sp 1
@item --no-support-ms-clr
@findex --no-support-ms-clr
Don't use Microsoft CLR specific workarounds in the generated code.

@sp 1
@item @code{--compile-to-c}
@itemx @code{--compile-to-C}
@findex --compile-to-c
An abbreviation for @samp{--target c --target-code-only}.
Generate C code in @file{@var{module}.c}, but do not invoke the
C compiler to generate object code.

@sp 1
@item @code{--java-only}
@findex --java-only
An abbreviation for @samp{--target java --target-code-only}.
Generate Java code in @file{@var{module}.java}, but do not invoke 
the Java compiler to produce Java bytecode.

@end table

@node LLDS back-end compilation model options
@subsection LLDS back-end compilation model options
@cindex LLDS back-end compilation model options

@table @asis

@sp 1
@item @code{--gcc-global-registers} (grades: reg, fast, asm_fast)
@itemx @code{--no-gcc-global-registers} (grades: none, jump, asm_jump)
@findex --gcc-global-registers
@findex --no-gcc-global-registers
Specify whether or not to use GNU C's global register variables extension.
This option is ignored if the @samp{--high-level-code} option is enabled.

@sp 1
@item @code{--gcc-non-local-gotos} (grades: jump, fast, asm_jump, asm_fast)
@itemx @code{--no-gcc-non-local-gotos} (grades: none, reg)
@findex --gcc-non-local-gotos
@findex --no-gcc-non-local-gotos
Specify whether or not to use GNU C's ``labels as values'' extension.
This option is ignored if the @samp{--high-level-code} option is enabled.

@sp 1
@item @code{--asm-labels} (grades: asm_jump, asm_fast)
@itemx @code{--no-asm-labels} (grades: none, reg, jump, fast)
@findex --asm-labels
@findex --no-asm-labels
Specify whether or not to use GNU C's asm extensions
for inline assembler labels.
This option is ignored if the @samp{--high-level-code} option is enabled.

@sp 1
@item @code{--pic-reg} (grades: any grade containing `.pic_reg')
@findex --pic-reg
@findex -fpic
@cindex Position independent code
@cindex PIC (position independent code)
@cindex Shared libraries
[For Unix with intel x86 architecture only.]
Select a register usage convention that is compatible
with position-independent code (gcc's `-fpic' option).
This is necessary when using shared libraries on Intel x86 systems
running Unix.  On other systems it has no effect.
This option is also ignored if the @samp{--high-level-code} option is enabled.

@end table

@node MLDS back-end compilation model options
@subsection MLDS back-end compilation model option
@cindex MLDS back-end compilation model options

@table @asis
@item @code{-H}, @code{--high-level-code} (grades: hlc, ilc, java)
@findex -H
@findex --high-level-code
Use an alternative back-end that generates high-level code
rather than the very low-level code that is generated by our
original back-end.

@end table

@node Optional features compilation model options
@subsection Optional features compilation model options
@cindex Optional features compilation model options

@table @asis
@sp 1
@item @code{--debug} (grades: any grade containing @samp{.debug})
@findex --debug
@cindex Debugging
Enables the inclusion in the executable of code and data structures
that allow the program to be debugged with @samp{mdb} (see @ref{Debugging}).
This option is not yet supported for the @samp{--high-level-code} back-ends.

@sp 1
@item @code{--profiling}, @code{--time-profiling} (grades: any grade containing @samp{.prof})
@cindex Profiling
@cindex Time profiling
@findex --profiling
@findex --time-profiling
Enable time profiling.  Insert profiling hooks in the
generated code, and also output some profiling
information (the static call graph) to the file
@samp{@var{module}.prof}.  @xref{Profiling}.
This option is not supported for the IL and Java back-ends.

@sp 1
@item @code{--memory-profiling} (grades: any grade containing @samp{.memprof})
@findex --memory-profiling
@cindex Profiling
@cindex Memory profiling
@cindex Heap profiling
@cindex Allocation profiling
Enable memory profiling.  Insert memory profiling hooks in the
generated code, and also output some profiling
information (the static call graph) to the file
@samp{@var{module}.prof}.  @xref{Using mprof for memory profiling}.
This option is not supported for the IL and Java back-ends.

@sp 1
@item @code{--deep-profiling} (grades: any grade containing @samp{.profdeep})
@findex --deep-profiling
@cindex Deep profiling
Enable deep profiling by inserting the appropriate hooks in the generated code.
This option is not supported for the high-level C, IL and Java back-ends.

@ignore
	The following are basically useless, hence undocumented.

@sp 1
@item @code{--profile-calls} (grades: any grade containing @samp{.profcalls})
@findex --profile-calls
Similar to @samp{--profiling}, except that this option only gathers
call counts, not timing information.  Useful on systems where time
profiling is not supported -- but not as useful as @samp{--memory-profiling}.

@sp 1
@item @code{--profile-time} (grades: any grade containing @samp{.proftime})
@findex --profile-time
Similar to @samp{--profiling}, except that this option only gathers
timing information, not call counts.  For the results to be useful,
call counts for an identical run of your program need to be gathered
using @samp{--profiling} or @samp{--profile-calls}.
XXX this doesn't work, because the code addresses change.
The only advantage of using @samp{--profile-time} and @samp{--profile-calls}
to gather timing information and call counts in separate runs,
rather than just using @samp{--profiling} to gather them both at once,
is that the former method can give slightly more accurate timing results.
because with the latter method the code inserted to record call counts
has a small effect on the execution speed.

@end ignore

@sp 1
@item @code{--gc @{none, conservative, accurate@}}
@itemx @code{--garbage-collection @{none, conservative, accurate@}}
@cindex Garbage collection
@cindex Conservative garbage collection
@cindex Accurate garbage collection
@findex --gc
@findex --garbage-collection
Specify which method of garbage collection to use.
Grades containing @samp{.gc} use @samp{--gc conservative},
other grades use @samp{--gc none}.
@samp{accurate} is not yet implemented.
This option is ignored by the IL and Java back-ends, which always use
the underlying IL or Java implementation's garbage collector.

@sp 1
@item @code{--use-trail} (grades: any grade containing @samp{.tr})
@findex --use-trail
@cindex Trailing
@cindex Constraint solving
@cindex Backtrackable destructive update
@cindex Destructive update, backtrackable
Enable use of a trail.
This is necessary for interfacing with constraint solvers,
or for backtrackable destructive update.
This option is not yet supported for the IL or Java back-ends.

@end table

@node Developer compilation model options
@subsection Developer compilation model options

@cindex Cross-compiling
Of the options listed below, the @samp{--num-tag-bits} option
may be useful for cross-compilation, but apart from that
these options are all experimental and are intended for
use by developers of the Mercury implementation rather than by
ordinary Mercury programmers.

@table @asis
@sp 1
@item @code{--tags @{none, low, high@}}
@findex --tags
@cindex Tags
@cindex Data representation
(This option is not intended for general use.)@*
Specify whether to use the low bits or the high bits of
each word as tag bits (default: low).

@sp 1
@item @code{--num-tag-bits @var{n}}
@findex --num-tag-bits
@cindex Tags
@cindex Data representation
(This option is not intended for general use.)@*
Use @var{n} tag bits.  This option is required if you specify
@samp{--tags high}.
With @samp{--tags low}, the default number of tag bits to use
is determined by the auto-configuration script.

@sp 1
@item @code{--num-reserved-addresses @var{n}}
@findex --reserved-addresses
@cindex Reserved addresses
@cindex Addresses, reserved
@cindex Data representation
(This option is not intended for general use.)@*
Treat the integer values from 0 up to @var{n} - 1 as reserved
addresses that can be used to represent nullary constructors
(constants) of discriminated union types.

@sp 1
@item @code{--num-reserved-objects @var{n}}
@findex --reserved-addresses
@cindex Reserved addresses
@cindex Reserved objects
@cindex Addresses, reserved
@cindex Objects, reserved
@cindex Data representation
(This option is not intended for general use.)@*
Allocate up to @var{n} - 1 global objects for representing nullary
constructors (constants) of discriminated union types.

Note that reserved objects will only be used if reserved addresses
(see @code{--num-reserved-addresses}) are not available, since the
latter are more efficient.

@sp 1
@item @code{--reserve-tag} (grades: any grade containing @samp{.rt})
@findex --reserve-tag
@cindex Tags
@cindex Data representation
Reserve a tag in the data representation of the generated 
code. This tag is intended to be used to give an explicit
representation to free variables.
This is necessary for a seamless Herbrand constraint solver --- 
for use with HAL.

@sp 1
@item @code{--no-type-layout}
@findex --no-type-layout
@findex --type-layout
(This option is not intended for general use.)@*
Don't output base_type_layout structures or references to them.
This option will generate smaller executables, but will not allow the
use of code that uses the layout information (e.g. @samp{functor},
@samp{arg}). Using such code will result in undefined behaviour at
runtime.  The C code also needs to be compiled with
@samp{-DNO_TYPE_LAYOUT}.

@end table

@node Code generation options
@section Code generation options
@cindex Code generation options

@table @code
@item --low-level-debug
@findex --low-level-debug
Enables various low-level debugging stuff that was in the distant past
used to debug the Mercury compiler's low-level code generation. 
This option is not likely to be useful to anyone except the Mercury
implementors.  It causes the generated code to become very big and very
inefficient, and slows down compilation a lot.

@sp 1
@item --pic
@findex --pic
@cindex Position independent code
@cindex PIC (position independent code)
Generate position independent code.
This option is only used by the @samp{--target asm} back-end.
The generated assembler will be written to @samp{@var{module}.pic_s}
rather than to @samp{@var{module}.s}.

@sp 1
@item --no-trad-passes
@findex --no-trad-passes
@findex --trad-passes
The default @samp{--trad-passes} completely processes each predicate
before going on to the next predicate.
This option tells the compiler
to complete each phase of code generation on all predicates
before going on the next phase on all predicates.

@c @sp 1
@c @item --no-polymorphism
@c Don't handle polymorphic types.
@c (Generates slightly more efficient code, but stops
@c polymorphism from working except in special cases.)

@sp 1
@item --no-reclaim-heap-on-nondet-failure
@findex --no-reclaim-heap-on-nondet-failure
@findex --reclaim-heap-on-nondet-failure
Don't reclaim heap on backtracking in nondet code.

@sp 1
@item --no-reclaim-heap-on-semidet-failure
@findex --no-reclaim-heap-on-semidet-failure
@findex --reclaim-heap-on-semidet-failure
Don't reclaim heap on backtracking in semidet code.

@sp 1
@item --no-reclaim-heap-on-failure
@findex --no-reclaim-heap-on-failure
@findex --reclaim-heap-on-failure
Combines the effect of the two options above.

@sp 1
@item --fact-table-max-array-size @var{size}
@findex --fact-table-max-array-size @var{size}
@cindex Fact tables
@cindex pragma fact_table
Specify the maximum number of elements in a single
@samp{pragma fact_table} data array (default: 1024).
The data for fact tables is placed into multiple C arrays, each with a
maximum size given by this option.  The reason for doing this is that
most C compilers have trouble compiling very large arrays.

@sp 1
@item --fact-table-hash-percent-full @var{percentage}
@findex --fact-table-hash-percent-full
@cindex Fact tables
@cindex pragma fact_table
Specify how full the @samp{pragma fact_table} hash tables should be
allowed to get.  Given as an integer percentage (valid range: 1 to 100,
default: 90).  A lower value means that the compiler will use
larger tables, but there will generally be less hash collisions,
so it may result in faster lookups.

@end table

@menu
* Code generation target options::
@end menu

@node Code generation target options
@subsection Code generation target options
@cindex Target options
@cindex Cross-compiling

The following options allow the Mercury compiler to optimize the generated
C code based on the characteristics of the expected target architecture.
The default values of these options will be whatever is appropriate
for the host architecture that the Mercury compiler was installed on,
so normally there is no need to set these options manually.  They might
come in handy if you are cross-compiling.  But even when cross-compiling,
it's probably not worth bothering to set these unless efficiency is
absolutely paramount.

@table @asis
@item @code{--have-delay-slot}
@findex --have-delay-slot
(This option is not intended for general use.)@*
Assume that branch instructions have a delay slot.

@sp 1
@item @code{--num-real-r-regs @var{n}}
@findex --num-real-r-regs
(This option is not intended for general use.)@*
Assume r1 up to r@var{n} are real general purpose registers.

@sp 1
@item @code{--num-real-f-regs @var{n}}
@findex --num-real-f-regs
(This option is not intended for general use.)@*
Assume f1 up to f@var{n} are real floating point registers.

@sp 1
@item @code{--num-real-r-temps @var{n}}
@findex --num-real-r-temps
(This option is not intended for general use.)@*
Assume that @var{n} non-float temporaries will fit into real machine registers.

@sp 1
@item @code{--num-real-f-temps @var{n}}
@findex --num-real-f-temps
(This option is not intended for general use.)@*
Assume that @var{n} float temporaries will fit into real machine registers.

@end table

@node Optimization options
@section Optimization options
@cindex Optimization options

@menu
* Overall optimization options::
* High-level (HLDS -> HLDS) optimization options::
* MLDS backend (MLDS -> MLDS) optimization options::
* Medium-level (HLDS -> LLDS) optimization options::
* Low-level (LLDS -> LLDS) optimization options::
* Output-level (LLDS -> C) optimization options::
@ifset aditi
* Aditi-RL optimization options::
@end ifset
@end menu

@node Overall optimization options
@subsection Overall optimization options

@table @code
@item -O @var{n}
@itemx --opt-level @var{n}
@itemx --optimization-level @var{n}
@findex -O
@findex --opt-level
@findex --optimization-level
@cindex Optimization levels
@cindex Compilation speed
@cindex Intermodule optimization
@cindex Cross-module optimization
Set optimization level to @var{n}.
Optimization levels range from -1 to 6.
Optimization level -1 disables all optimizations,
while optimization level 6 enables all optimizations
except for the cross-module optimizations listed below.
Some experimental optimizations (for example constraint
propagation) are not be enabled at any optimization level.

In general, there is a trade-off between compilation speed and the
speed of the generated code.  When developing, you should normally use
optimization level 0, which aims to minimize compilation time.  It
enables only those optimizations that in fact usually @emph{reduce}
compilation time.  The default optimization level is level 2, which
delivers reasonably good optimization in reasonable time.  Optimization
levels higher than that give better optimization, but take longer,
and are subject to the law of diminishing returns.  The difference in
the quality of the generated code between optimization level 5 and
optimization level 6 is very small, but using level 6 may increase
compilation time and memory requirements dramatically.

Note that if you want the compiler to perform cross-module
optimizations, then you must enable them separately;
the cross-module optimizations are not enabled by any @samp{-O}
level, because they affect the compilation process in ways
that require special treatment by @samp{mmake}.

@sp 1
@item --opt-space
@itemx --optimize-space
@findex --opt-space
@findex --optimize-space
@findex Optimizing space
@findex Optimizing code size
Turn on optimizations that reduce code size
and turn off optimizations that significantly increase code size.
@end table

@table @code
@item --intermodule-optimization
@findex --intermodule-optimization
@cindex Intermodule optimization
@cindex Cross-module optimization
@cindex Inlining
Perform inlining and higher-order specialization of the code for
predicates or functions imported from other modules.

@sp 1
@item --trans-intermod-opt
@itemx --transitive-intermodule-optimization
@findex --trans-intermod-opt
@findex --transitive-intermodule-optimization
@cindex Transitive intermodule optimization
@cindex Intermodule optimization, transitive
@cindex Cross-module optimization, transitive
@cindex Termination analysis
Use the information stored in @file{@var{module}.trans_opt} files
to make intermodule optimizations.  The @file{@var{module}.trans_opt} files
are different to the @file{@var{module}.opt} files as @samp{.trans_opt}
files may depend on other @samp{.trans_opt} files, whereas each
@samp{.opt} file may only depend on the corresponding @samp{.m} file. 

@item --use-opt-files
@findex --use-opt-files
Perform inter-module optimization using any @samp{.opt} files which are 
already built, e.g. those for the standard library, but do not build any
others.

@item --use-trans-opt-files
@findex --use-trans-opt-files
Perform inter-module optimization using any @samp{.trans_opt} files which are 
already built, e.g. those for the standard library, but do not build any
others.

@sp 1
@item --split-c-files
@findex --split-c-files
@findex --optimize-dead-procs
@cindex Optimizing code size
@cindex Optimizing space
Generate each C function in its own C file,
so that the linker will optimize away unused code.
This has the same effect as @samp{--optimize-dead-procs},
except that it works globally at link time, rather than
over a single module, so it does a much better job of
eliminating unused procedures.
This option significantly increases compilation time,
link time, and intermediate disk space requirements,
but in return reduces the size of the final
executable, typically by about 10-20%.
This option is only useful with @samp{--procs-per-c-function 1},
so this option automatically sets @samp{--procs-per-c-function 1}.

@findex --high-level-code
The @samp{--high-level-code} back-end does not support
@samp{--split-c-files}.

N.B.  When using @samp{mmake}, the @samp{--split-c-files} option should
not be placed in the @samp{MCFLAGS} variable.  Instead, use the
@samp{@var{MODULE}.split} target, i.e. type @samp{mmake foo.split}
rather than @samp{mmake foo}.

@end table

@node High-level (HLDS -> HLDS) optimization options
@subsection High-level (HLDS -> HLDS) optimization options
@cindex HLDS

These optimizations are high-level transformations on our HLDS (high-level
data structure).

@table @code
@item --no-inlining
@findex --no-inlining
@findex --inlining
@cindex Inlining
Disable all forms of inlining.

@item --no-inline-simple
@findex --no-inline-simple
@findex --inline-simple
Disable the inlining of simple procedures.

@item --no-inline-single-use
@findex --no-inline-single-use
@findex --inline-single-use
Disable the inlining of procedures called only once.

@item --inline-compound-threshold @var{threshold}
@findex --inline-compound-threshold
Inline a procedure if its size
(measured roughly in terms of the number of connectives in its internal form),
multiplied by the number of times it is called,
is below the given threshold.

@item --inline-simple-threshold @var{threshold}
@findex --inline-simple-threshold
Inline a procedure if its size is less than the given threshold.

@item --intermod-inline-simple-threshold @var{threshold}
@findex --intermod-inline-simple-threshold
Similar to --inline-simple-threshold, except used to determine which
predicates should be included in @samp{.opt} files.  Note that changing this
between writing the @samp{.opt} file and compiling to C may cause link errors,
and too high a value may result in reduced performance.

@item --inline-vars-threshold @var{threshold}
@findex --inline-vars-threshold
Don't inline a call if it would result in a procedure
containing more than @var{threshold} variables. Procedures
containing large numbers of variables can cause
slow compilation.

@sp 1
@item --no-common-struct
@findex --no-common-struct
@findex --common-struct
Disable optimization of common term structures.

@sp 1
@item --no-common-goal
@findex --no-common-goal
@findex --common-goal
Disable optimization of common goals.
At the moment this optimization
detects only common deconstruction unifications.
Disabling this optimization reduces the class of predicates
that the compiler considers to be deterministic.

@item --constraint-propagation
@findex --constraint-propagation
Enable the constraint propagation transformation,
which attempts to transform the code so that goals
which can fail are executed as early as possible.

@item --local-constraint-propagation
@findex --local-constraint-propagation
Enable the constraint propagation transformation,
but only rearrange goals within each procedure.
Specialized versions of procedures will not be created.

@c @sp 1
@c @item --prev-code
@c @findex --prev-code
@c Migrate into the start of branched goals.

@sp 1
@item --no-follow-code
@findex --no-follow-code
@findex --follow-code
Don't migrate builtin goals into branched goals.

@sp 1
@item --optimize-unused-args
@findex --optimize-unused-args
@cindex Unused arguments
Remove unused predicate arguments.  The compiler will
generate more efficient code for polymorphic predicates.

@sp 1
@item --intermod-unused-args
@findex --intermod-unused-args
@cindex Unused arguments
Perform unused argument removal across module boundaries.
This option implies @samp{--optimize-unused-args} and
@samp{--intermodule-optimization}.

@sp 1
@item --unneeded-code
@findex --unneeded-code
@cindex Unused outputs
Remove goals from computation paths where their outputs are not needed,
provided the language semantics options allow the deletion or movement
of the goal.

@sp 1
@item --unneeded-code-copy-limit
@findex --unneeded-code-copy-limit
Gives the maximum number of places to which a goal may be copied
when removing it from computation paths on which its outputs are not needed.
A value of zero forbids goal movement and allows only goal deletion;
a value of one prevents any increase in the size of the code.

@sp 1
@item --optimize-higher-order
@findex --optimize-higher-order
@cindex Higher-order specialization
@cindex Specialization of higher-order calls
Specialize calls to higher-order predicates where
the higher-order arguments are known.

@sp 1
@item --type-specialization
@findex --type-specialization
@cindex Type specialization
Specialize calls to polymorphic predicates where
the polymorphic types are known.

@sp 1
@item --user-guided-type-specialization
@findex --user-guided-type-specialization
@cindex Type specialization, user guided
Enable specialization of polymorphic predicates for which
there are `:- pragma type_spec' declarations.
See the ``Type specialization'' section in the ``Pragmas''
chapter of the Mercury Language Reference Manual for more details.

@sp 1
@item --higher-order-size-limit
@findex --higher-order-size-limit
Set the maximum goal size of specialized versions created by
@samp{--optimize-higher-order} and @samp{--type-specialization}.
Goal size is measured as the number of calls, unifications
and branched goals.

@sp 1
@item --higher-order-arg-limit
@item --higher-order-arg-limit
Set the maximum size of higher-order arguments to
be specialized by @samp{--optimize-higher-order} and
@samp{--type-specialization}.

@sp 1
@item --optimize-constant-propagation
@findex --optimize-constant-propagation
Evaluate constant expressions at compile time.

@sp 1
@item --introduce-accumulators
@findex --introduce-accumulators
@cindex Accumulator introduction
@cindex Tail recursion optimization
@cindex Last call optimization
Attempt to introduce accumulating variables into
procedures, so as to make the procedure tail recursive.

@sp 1
@item --optimize-constructor-last-call
@findex --optimize-constructor-last-call
@cindex Tail recursion optimization
@cindex Last call optimization
Enable the optimization of ``last'' calls that are followed by
constructor application.

@sp 1
@item --optimize-dead-procs
@findex --optimize-dead-procs
@cindex Dead procedure elimination
@cindex Dead predicate elimination
@cindex Dead function elimination
@cindex Unused procedure elimination
Enable dead procedure elimination.

@sp 1
@item --excess-assign
@findex --excess-assign
Remove excess assignment unifications.

@sp 1
@item --optimize-duplicate-calls
@findex --optimize-duplicate-calls
@cindex Duplicate call optimization
Optimize away multiple calls to a predicate with the same input arguments.

@sp 1
@item --delay-constructs
@findex --delay-constructs
Reorder goals to move construction unifications after
primitive goals that can fail.

@sp 1
@item --optimize-saved-vars
@findex --optimize-saved-vars
Minimize the number of variables that have to be saved across calls.

@sp 1
@item --deforestation
@findex --deforestation
Enable deforestation. Deforestation is a program transformation whose aim
is to avoid the construction of intermediate data structures and to avoid
repeated traversals over data structures within a conjunction.

@sp 1
@item --deforestation-depth-limit
@findex --deforestation-depth-limit
Specify a depth limit to prevent infinite loops in the
deforestation algorithm.
A value of -1 specifies no depth limit. The default is 4.

@sp 1
@item --deforestation-vars-threshold
@findex --deforestation-vars-threshold
Specify a rough limit on the number of variables
in a procedure created by deforestation.
A value of -1 specifies no limit. The default is 200.

@sp 1
@item --deforestation-size-threshold
@findex --deforestation-size-threshold
Specify a rough limit on the size of a goal
to be optimized by deforestation.
A value of -1 specifies no limit. The default is 15.

@end table

@node MLDS backend (MLDS -> MLDS) optimization options
@subsection MLDS backend (MLDS -> MLDS) optimization options
@cindex MLDS

These optimizations are applied to the medium level 
intermediate code.

@table @code
@item --no-mlds-optimize
@findex --no-mlds-optimize
@findex --mlds-optimize
Disable the MLDS -> MLDS optimization passes.

@sp 1
@item --no-optimize-tailcalls
@findex --no-optimize-tailcalls
@findex --optimize-tailcalls
Treat tailcalls as ordinary calls rather than optimizing
by turning self-tailcalls into loops.

@item --no-optimize-initializations
@findex --no-optimize-initializations
@findex --optimize-initializations
Leave initializations of local variables as assignment statements,
rather than converting such assignments statements into initializers.

@item --eliminate-local-variables
@findex --no-eliminate-local-variables
@findex --eliminate-local-variables
Eliminate local variables with known values, where possible,
by replacing occurrences of such variables with their values.
@end table

@node Medium-level (HLDS -> LLDS) optimization options
@subsection Medium-level (HLDS -> LLDS) optimization options
@cindex HLDS
@cindex LLDS

These optimizations are applied during the process of generating
low-level intermediate code from our high-level data structure.

@table @code
@item --no-static-ground-terms
@findex --no-static-ground-terms
@findex --static-ground-terms
Disable the optimization of constructing constant ground terms
at compile time and storing them as static constants.
Note that auxiliary data structures created by the compiler
for purposes such as debugging
will still be created as static constants.

@sp 1
@item --no-smart-indexing
@findex --no-smart-indexing
@findex --smart-indexing
Generate switches as a simple if-then-else chains;
disable string hashing and integer table-lookup indexing.

@sp 1
@item --dense-switch-req-density @var{percentage}
@findex --dense-switch-req-density
The jump table generated for an atomic switch
must have at least this percentage of full slots (default: 25).

@sp 1
@item --dense-switch-size @var{size}
@findex --dense-switch-size
The jump table generated for an atomic switch
must have at least this many entries (default: 4).

@sp 1
@item --lookup-switch-req-density @var{percentage}
@findex --lookup-switch-req-density
The lookup tables generated for an atomic switch
in which all the outputs are constant terms
must have at least this percentage of full slots (default: 25).

@sp 1
@item --lookup-switch-size @var{size}
@findex --lookup-switch-size
The lookup tables generated for an atomic switch
in which all the outputs are constant terms
must have at least this many entries (default: 4).

@sp 1
@item --string-switch-size @var{size}
@findex --string-switch-size
The hash table generated for a string switch
must have at least this many entries (default: 8).

@sp 1
@item --tag-switch-size @var{size}
@findex --tag-switch-size
The number of alternatives in a tag switch
must be at least this number (default: 3).

@sp 1
@item --try-switch-size @var{size}
@findex --try-switch-size
The number of alternatives in a try-chain switch
must be at least this number (default: 3).

@sp 1
@item --binary-switch-size @var{size}
@findex --binary-switch-size
The number of alternatives in a binary search switch
must be at least this number (default: 4).

@sp 1
@item --no-middle-rec
@findex --no-middle-rec
@findex --middle-rec
Disable the middle recursion optimization.

@sp 1
@item --no-simple-neg
@findex --no-simple-neg
@findex --simple-neg
Don't generate simplified code for simple negations.

@sp 1
@item --no-follow-vars
@findex --follow-vars
@findex --no-follow-vars
Don't optimize the assignment of registers in branched goals.

@end table

@node Low-level (LLDS -> LLDS) optimization options
@subsection Low-level (LLDS -> LLDS) optimization options
@cindex LLDS

These optimizations are transformations that are applied to our
low-level intermediate code before emitting C code.

@table @code
@item --no-common-data
@findex --no-common-data
@findex --common-data
Disable optimization of common data structures.

@item --no-llds-optimize
@findex --no-llds-optimize
@findex --llds-optimize
Disable the low-level optimization passes.

@sp 1
@item --no-optimize-peep
@findex --no-optimize-peep
@findex --optimize-peep
Disable local peephole optimizations.

@sp 1
@item --no-optimize-jumps
@findex --no-optimize-jumps
@findex --optimize-jumps
Disable elimination of jumps to jumps.

@sp 1
@item --no-optimize-fulljumps
@findex --no-optimize-fulljumps
@findex --optimize-fulljumps
Disable elimination of jumps to ordinary code.

@sp 1
@item --pessimize-tailcalls
@findex --pessimize-tailcalls
Disable the optimization of tailcalls.

@sp 1
@item --checked-nondet-tailcalls
@findex --checked-nondet-tailcalls
Convert nondet calls into tail calls whenever possible, even
when this requires a runtime check. This option tries to
minimize stack consumption, possibly at the expense of speed.

@sp 1
@item --use-local-vars
@findex --use-local-vars
Disable the transformation to use local variables in C code
blocks whereever possible.

@sp 1
@item --no-optimize-labels
@findex --no-optimize-labels
@findex --optimize-labels
Disable elimination of dead labels and code.

@sp 1
@item --optimize-dups
@findex --optimize-dups
Enable elimination of duplicate code.

@c @sp 1
@c @item --optimize-copyprop
@c Enable the copy propagation optimization.

@sp 1
@item --no-optimize-frames
@findex --no-optimize-frames
@findex --optimize-frames
Disable stack frame optimizations.

@sp 1
@item --no-optimize-delay-slot
@findex --no-optimize-delay-slot
@findex --optimize-delay-slot
Disable branch delay slot optimizations.

@sp 1
@item --optimize-reassign
@findex --optimize-reassign
Optimize away assignments to locations that already hold the assigned value.

@sp 1
@item --optimize-repeat @var{n}
@findex --optimize-repeat
Iterate most optimizations at most @var{n} times (default: 3).

@end table

@node Output-level (LLDS -> C) optimization options
@subsection Output-level (LLDS -> C) optimization options

These optimizations are applied during the process of generating
C intermediate code from our low-level data structure.

@table @code
@item --no-emit-c-loops
@findex --no-emit-c-loops
Use only gotos --- don't emit C loop constructs.

@sp 1
@item --use-macro-for-redo-fail
@findex --use-macro-for-redo-fail
Emit the fail or redo macro instead of a branch
to the fail or redo code in the runtime system.

@sp 1
@item --procs-per-c-function @var{n}
@findex --procs-per-c-function
Don't put the code for more than @var{n} Mercury
procedures in a single C function.  The default
value of @var{n} is one.  Increasing @var{n} can produce
slightly more efficient code, but makes compilation slower.
Setting @var{n} to the special value zero has the effect of
putting all the procedures in a single function,
which produces the most efficient code
but tends to severely stress the C compiler.

@end table

@ifset aditi
@node Aditi-RL optimization options
@subsection Aditi-RL optimization options

These optimizations are applied to the Aditi-RL code produced
for predicates with @samp{:- pragma aditi(@dots{})} declarations
(@pxref{Using Aditi}).

@table @code
@item --optimize-rl
@findex --optimize-rl
Enable the optimizations of Aditi-RL procedures described below.

@sp 1
@item --optimize-rl-cse
@findex --optimize-rl-cse
Optimize common subexpressions in Aditi-RL procedures.

@sp 1
@item --optimize-rl-invariants
@findex --optimize-rl-invariants
Optimize loop invariants in Aditi-RL procedures.

@sp 1
@item --optimize-rl-index
@findex --optimize-rl-index
Use indexing to optimize access to relations in Aditi-RL procedures.

@sp 1
@item --detect-rl-streams
@findex --detect-rl-streams
Detect cases where intermediate results in Aditi-RL procedures
do not need to be materialised.
@end table
@end ifset
@c aditi

@node Build system options
@section Build system options
@table @code
@item -m
@itemx --make
@findex -m
@findex --make
Treat the non-option arguments to @samp{mmc} as files to
make, rather than source files.

@item -r
@itemx --rebuild
@findex -r
@findex --rebuild
Same as @samp{--make}, but always rebuild the target files
even if they are up to date.

@item -k
@itemx --keep-going
@findex -k
@findex --keep-going
With @samp{--make} keep going as far as
possible even if an error is detected.

@item --install-prefix @var{dir}
@findex --install-prefix
Specify the directory under which to install Mercury libraries.

@item --install-command @var{command}
@findex --install-command
Specify the command to use to install the files in Mercury
libraries. The given command will be invoked as
@code{@var{command} @var{source} @var{target}}
to install each file in a Mercury library.
The default command is @samp{cp}.

@item --libgrade @var{grade}
@findex --libgrade
Add @var{grade} to the list of compilation grades in
which a library to be installed should be built.

@item --options-file @var{file}
@findex --options-file
Add @var{file} to the list of options files to be processed.
If no @samp{--options-file} options are given, the file
@file{Mercury.options} in the current directory will be
read if it exists.

@item --options-search-directory @var{dir}
Add @var{dir} to the list of directories to be searched for
options files.

@item -I @var{dir}
@itemx --search-directory @var{dir}
@findex -I
@findex --search-directory
@cindex Directories
@cindex Search path
Append @var{dir} to the list of directories to be searched for
imported modules.

@item --intermod-directory @var{dir}
@findex --intermod-directory
@cindex Directories
@cindex Search path
Append @var{dir} to the list of directories to be searched for
@samp{.opt} files.

@item --use-search-directories-for-intermod
@findex --use-search-directories-for-intermod
@cindex Directories
@cindex Search path
Append the arguments of all -I options to the list of directories
to be searched for @samp{.opt} files.

@item --use-subdirs
@findex --use-subdirs
@cindex File names
@cindex Directories
@cindex Subdirectories
@cindex @file{Mercury} subdirectory
Create intermediate files in a @file{Mercury} subdirectory,
rather than in the current directory.

@end table

@node Miscellaneous options
@section Miscellaneous options
@table @code

@sp 1
@item -?
@itemx -h
@itemx --help
@findex -?
@findex -h
@findex --help
@cindex Help option
Print a usage message.

@sp 1
@item --filenames-from-stdin
@findex --filenames-from-stdin
Read then compile a newline terminated module name or file name from the
standard input. Repeat this until EOF is reached. (This allows a program
or user to interactively compile several modules without the overhead of
process creation for each one.)

@ifset aditi
@sp 1
@item --aditi
@findex --aditi
Enable Aditi compilation.  You need to enable this option if you
are making use of the Aditi deductive database interface (@pxref{Using Aditi}).

@sp 1
@item --aditi-user
@findex --aditi-user
Specify the Aditi login of the owner of the predicates in any Aditi RL
files produced if no @samp{:- pragma owner(@dots{})} declaration is given.
The owner field is used along with module, name and arity to identify
predicates, and is also used for security checks. Defaults to the value
of the @samp{USER} environment variable. If @samp{USER} is not set,
@samp{--aditi-user} defaults to the string ``guest''.

@end ifset
@c aditi
@end table

@node Target code compilation options
@section Target code compilation options
@cindex Target code compilation options

If you are using Mmake, you need to pass these options
to the target code compiler (e.g. @samp{mgnuc}) rather
than to @samp{mmc}.

@table @code
@sp 1
@item @code{--target-debug}
@findex @code{--target-debug}
@findex @code{--c-debug}
@findex @code{/debug}
Enable debugging of the generated target code.
If the target language is C, this has the same effect as
@samp{--c-debug} (see below).
If the target language is IL, this causes the compiler to
pass @samp{/debug} to the IL assembler.

@sp 1
@item --cc @var{compiler-name}
@findex --cc
@cindex C compiler
Specify which C compiler to use.

@sp 1
@item --c-include-directory @var{dir}
@findex --c-include-directory
@cindex Include directories
@cindex Directories
Append @var{dir} to the list of directories to be searched for
C header files.  Note that if you want to override this list, rather than
append to it, then you can set the @samp{MERCURY_MC_ALL_C_INCL_DIRS}
environment variable to a sequence of @samp{--c-include-directory} options.

@sp 1
@item @code{--c-debug}
@findex --c-debug
@cindex C debugging
@cindex Debugging the generated C code
Pass the @samp{-g} flag to the C compiler, to enable debugging
of the generated C code, and also pass @samp{--no-strip} to the Mercury
linker, to tell it not to strip the C debugging information.
Since the generated C code is very low-level, this option is not likely
to be useful to anyone except the Mercury implementors, except perhaps
for debugging code that uses Mercury's C interface extensively.

@item --no-c-optimize
@findex --no-c-optimize
Don't enable the C compiler's optimizations.

@sp 1
@item --inline-alloc
@findex --inline-alloc
Inline calls to @samp{GC_malloc()}.
This can improve performance a fair bit,
but may significantly increase code size.
This option has no effect if @samp{--gc conservative}
is not set or if the C compiler is not GNU C.

@sp 1
@item --cflags @var{options}
@findex --cflags
@cindex C compiler options
Specify options to be passed to the C compiler.

@sp 1
@item --javac @var{compiler-name}
@item --java-compiler @var{compiler-name}
@findex --javac
@findex --java-compiler
@cindex Java compiler
Specify which Java compiler to use.  The default is @samp{javac}.

@sp 1
@item --java-flags @var{options}
@findex --java-flags
@cindex Java compiler options
Specify options to be passed to the Java compiler.

@sp 1
@item --java-classpath @var{dir}
@findex --java-classpath
@cindex classpath
@cindex Directories
Set the classpath for the Java compiler.

@sp 1
@item --java-object-file-extension @var{extension}
@findex --java-object-file-extension
@cindex File extensions
Specify an extension for Java object (bytecode) files.  By default this
is @samp{.class}. 

@end table

@node Link options
@section Link options
@cindex Link options
@cindex Linker options
@table @code
@sp 1
@item -o @var{filename}
@itemx --output-file @var{filename}
@findex -o
@findex --output-file
Specify the name of the final executable.
(The default executable name is the same as the name of the
first module on the command line, but without the @samp{.m} extension.)

@sp 1
@item --link-flags @var{options}
@findex --link-flags
@cindex Link options
@cindex Linker options
Specify options to be passed to @samp{ml}, the Mercury linker.

@sp 1
@item -L @var{directory}
@itemx --library-directory @var{directory}
@findex -L
@findex --library-directory
@cindex Directories for libraries
@cindex Search path for libraries
Append @var{directory} to the list of directories in which
to search for libraries.

@item -l @var{library}
@itemx --library @var{library}
@findex -l
@findex --library
@cindex Libraries, linking with
Link with the specified library.

@item --link-object @var{object}
@findex --link-object
@cindex Object files, linking with
Link with the specified object file.

@item --mld @var{directory}
@itemx --mercury-library-directory @var{directory}
@findex --mld
@findex --mercury-library-directory
@cindex Directories for libraries
@cindex Search path for libraries
Append @var{directory} to the list of directories to
be searched for Mercury libraries.
This will add @samp{--search-directory}, @samp{--library-directory},
@samp{--init-file-directory} and @samp{--c-include-directory}
options as needed.  @xref{Using libraries}.

@item --ml @var{library}
@itemx --mercury-library @var{library}
@findex --ml
@findex --mercury-library
@cindex Libraries, linking with
Link with the specified Mercury library.  @xref{Using libraries}.

@item --mercury-standard-library-directory @var{directory}
@itemx --mercury-stdlib-dir @var{directory}
@findex --mercury-standard-library-directory
@findex --mercury-stdlib-dir
Search @var{directory} for the Mercury standard library.

@item --no-mercury-standard-library-directory
@itemx --no-mercury-stdlib-dir
@findex --no-mercury-standard-library-directory
@findex --no-mercury-stdlib-dir
Don't use the Mercury standard library.

@item --init-file-directory @var{directory}
@findex --init-file-directory
Append @var{directory} to the list of directories to
be searched for @samp{.init} files by @samp{c2init}.

@item --init-file @var{file}
@findex --init-file
Append @var{file} to the list of @samp{.init} files
to be passed to @samp{c2init}.

@item --trace-init-file @var{file}
@findex --trace-init-file
Append @var{file} to the list of @samp{.init} files
to be passed to @samp{c2init} when tracing is enabled.

@end table

@c ----------------------------------------------------------------------------

@node Environment
@chapter Environment variables
@cindex Environment variables
@cindex Variables, environment
@cindex Directories
@cindex Search path

The shell scripts in the Mercury compilation environment
will use the following environment variables if they are set.
There should be little need to use these, because the default
values will generally work fine.

@table @code
@item MERCURY_DEFAULT_GRADE
@vindex MERCURY_DEFAULT_GRADE
The default grade to use if no @samp{--grade} option is specified.

@item MERCURY_STDLIB_DIR
@vindex MERCURY_STDLIB_DIR
The directory containing the installed Mercury standard library.
If the MERCURY_ALL_C_INCL_DIRS, MERCURY_ALL_MC_C_INCL_DIRS,
MERCURY_INT_DIR, MERCURY_MOD_LIB_MODS and MERCURY_TRACE_LIB_MODS
variables are set the value of MERCURY_STDLIB_DIR will be ignored.

@sp 1
@item MERCURY_ALL_C_INCL_DIRS
@vindex MERCURY_ALL_C_INCL_DIRS
A list of options for the C compiler that specifies
all the directories the C compiler should search for the C header files
of the Mercury runtime system and garbage collector.
The default value of this variable is @samp{-I$MERCURY_STDLIB_DIR/inc},
since usually all these header files are installed in one directory.
This environment variable is used by @samp{mgnuc};
it should generally be kept in sync with
@code{MERCURY_ALL_MC_C_INCL_DIRS}, which is used by @samp{mmc}.

@sp 1
@item MERCURY_ALL_MC_C_INCL_DIRS
@vindex MERCURY_ALL_MC_C_INCL_DIRS
A list of options for mmc that specifies
all the directories it should search for the C header files
of the Mercury runtime system and garbage collector.
The default value of this variable is
@samp{--c-include-directory $MERCURY_STDLIB_DIR/inc},
since usually all these header files are installed in one directory.
This environment variable is used by @samp{mmc};
it should generally be kept in sync with
@code{MERCURY_ALL_C_INCL_DIRS}, which is used by @samp{mgnuc}.

@sp 1
@item MERCURY_INT_DIR
@vindex MERCURY_INT_DIR
Directory for the Mercury library interface
files (@file{*.int}, @file{*.int2}, @file{*.int3} and @file{*.opt}).

@sp 1
@item MERCURY_C_LIB_DIR
@vindex MERCURY_C_LIB_DIR
Base directory containing the Mercury libraries (@file{libmer_*.a} and
possibly @file{libmer_*.so}) for each configuration and grade.
The libraries for each configuration and grade should
be in the subdirectory @var{config}/@var{grade} of @code{$MERCURY_C_LIB_DIR}.

@sp 1
@item MERCURY_NONSHARED_LIB_DIR
@vindex MERCURY_NONSHARED_LIB_DIR
For IRIX 5, this environment variable can be used to specify a
directory containing a version of libgcc.a which has been compiled with
@samp{-mno-abicalls}.  See the file @samp{README.IRIX-5} in the Mercury
source distribution.

@item MERCURY_MOD_LIB_MODS
@vindex MERCURY_MOD_LIB_MODS
The names of the .init files in the Mercury library.

@item MERCURY_TRACE_LIB_MODS
@vindex MERCURY_TRACE_LIB_MODS
The names of the .init files in the Mercury library which should
only be used when tracing is enabled.

@sp 1
@item MERCURY_COMPILER
@vindex MERCURY_COMPILER
Filename of the Mercury Compiler.

@sp 1
@item MERCURY_MKINIT
@vindex MERCURY_MKINIT
Filename of the program to create the @file{*_init.c} file.

@sp 1
@item MERCURY_DEBUGGER_INIT
@vindex MERCURY_DEBUGGER_INIT
Name of a file that contains startup commands for the Mercury debugger.
This file should contain documentation for the debugger command set,
and possibly a set of default aliases.

@sp 1
@item MERCURY_OPTIONS
@vindex MERCURY_OPTIONS
A list of options for the Mercury runtime that gets
linked into every Mercury program.  Options may also
be set at compile time by passing @samp{--runtime-flags}
options to @samp{ml} and @samp{c2init}.
The Mercury runtime accepts the following options.

@sp 1
@table @code

@c @item -a
@c If given force a redo when the entry point procedure succeeds;
@c this is useful for benchmarking when this procedure is model_non.

@c @item -c
@c Check how much of the space reserved for local variables
@c by mercury_engine.c was actually used.

@item -C @var{size}
@findex -C (runtime option)
Tells the runtime system
to optimize the locations of the starts of the various data areas
for a primary data cache of @var{size} kilobytes.
The optimization consists of arranging the starts of the areas
to differ as much as possible modulo this size.

@c @item -d @var{debugflag}
@c @findex -d (runtime option)
@c Sets a low-level debugging flag.
@c These flags are consulted only if
@c the runtime was compiled with the appropriate definitions;
@c most of them depend on MR_LOWLEVEL_DEBUG.
@c For the meanings of the debugflag parameters,
@c see process_options() in mercury_wrapper.c
@c and do a grep for the corresponding variable.

@sp 1
@item -D @var{debugger}
@findex -D (runtime option)
Enables execution tracing of the program,
via the internal debugger if @var{debugger} is @samp{i}
and via the external debugger if @var{debugger} is @samp{e}.
(The mdb script works by including @samp{-Di} in MERCURY_OPTIONS.)
The external debugger is not yet available.

@sp 1
@item -p
@findex -p (runtime option)
Disables profiling.
This only has an effect if the executable was built in a profiling grade.

@sp 1
@item -P @var{num}
@findex -P (runtime option)
Tells the runtime system to use @var{num} threads
if the program was built in a parallel grade.

@c @item -r @var{num}
@c @findex -r (runtime option)
@c Repeats execution of the entry point procedure @var{num} times,
@c to enable accurate timing.

@c @item -t
@c @findex -t (runtime option)
@c Tells the runtime system to measure the time taken by
@c the (required number of repetitions of) the program,
@c and to print the result of this time measurement.

@sp 1
@item -T @var{time-method}
@findex -T (runtime option)
If the executable was compiled in a grade that includes time profiling,
this option specifies what time is counted in the profile.
@var{time-method} must have one of the following values:

@sp 1
@table @code
@item @samp{r}
Profile real (elapsed) time (using ITIMER_REAL).
@item @samp{p}
Profile user time plus system time (using ITIMER_PROF).
This is the default.
@item @samp{v}
Profile user time (using ITIMER_VIRTUAL).
@end table

@sp 1
Currently, the @samp{-Tp} and @samp{-Tv} options don't work on Windows,
so on Windows you must explicitly specify @samp{-Tr}.
@c the above sentence is duplicated above

@c @item -x
@c @findex -x (runtime option)
@c Tells the Boehm collector not to perform any garbage collection.

@sp 1
@item --heap-size @var{size}
@findex --heap-size (runtime option)
Sets the size of the heap to @var{size} kilobytes.

@sp 1
@item --detstack-size @var{size}
@findex --detstack-size (runtime option)
Sets the size of the det stack to @var{size} kilobytes.

@sp 1
@item --nondetstack-size @var{size}
@findex --nondetstack-size (runtime option)
Sets the size of the nondet stack to @var{size} kilobytes.

@sp 1
@item --solutions-heap-size @var{size}
@findex --solutions-heap-size (runtime option)
Sets the size of the solutions heap to @var{size} kilobytes.

@sp 1
@item --trail-size @var{size}
@findex --trail-size
@cindex Trail size
Sets the size of the trail to @var{size} kilobytes.

@c @sp 1
@c @item --heap-redzone-size @var{size}
@c @findex --heap-redzone-size (runtime option)
@c Sets the size of the redzone on the heap to @var{size} kilobytes.

@c @sp 1
@c @item --detstack-redzone-size @var{size}
@c @findex --detstack-redzone-size (runtime option)
@c Sets the size of the redzone on the det stack to @var{size} kilobytes.

@c @sp 1
@c @item --nondetstack-redzone-size @var{size}
@c @findex --nondetstack-redzone-size (runtime option)
@c Sets the size of the redzone on the nondet stack to @var{size} kilobytes.

@c @sp 1
@c @item --trail-redzone-size @var{size}
@c @findex --trail-redzone-size (runtime option)
@c Sets the size of the redzone on the trail to @var{size} kilobytes.

@sp 1
@item -i @var{filename}
@itemx --mdb-in @var{filename}
@findex -i (runtime option)
@findex --mdb-in (runtime option)
Read debugger input from the file or device specified by @var{filename},
rather than from standard input.

@sp 1
@item -o @var{filename}
@itemx --mdb-out @var{filename}
Print debugger output to the file or device specified by @var{filename},
@findex -o (runtime option)
@findex --mdb-out (runtime option)
rather than to standard output.

@sp 1
@item -e @var{filename}
@itemx --mdb-err @var{filename}
@findex -e (runtime option)
@findex --mdb-err (runtime option)
Print debugger error messages to the file or device specified by @var{filename},
rather than to standard error.

@sp 1
@item -m @var{filename}
@itemx --mdb-tty @var{filename}
@findex -m (runtime option)
@findex --mdb-tty (runtime option)
Redirect all three debugger I/O streams -- input, output, and error messages --
to the file or device specified by @var{filename}.

@c --mdb-in-window is for use only by the mdb script, so it's
@c not documented here.

@end table

@end table

@c ----------------------------------------------------------------------------

@node C compilers
@chapter Using a different C compiler
@cindex C compilers
@cindex Using a different C compiler
@cindex GNU C
@findex --cc

The Mercury compiler takes special advantage of certain extensions
provided by GNU C to generate much more efficient code.  We therefore
recommend that you use GNU C for compiling Mercury programs.
However, if for some reason you wish to use another compiler,
it is possible to do so.  Here's what you need to do.

@itemize @bullet
@item You must specify the name of the new compiler.
You can do this either by setting the @samp{MERCURY_C_COMPILER}
environment variable, by adding
@samp{MGNUC=MERCURY_C_COMPILER=@dots{} mgnuc} to your @samp{Mmake} file,
or by using the @samp{--cc} option to @samp{mmc}.
You may need to specify some option(s) to the C compiler
to ensure that it uses an ANSI preprocessor (e.g. if you
are using the DEC Alpha/OSF 3.2 C compiler, you would need to
pass @samp{--cc="cc -std"} to @samp{mmc} so that it will pass the
@samp{-std} option to @samp{cc}).

@item
You must use the grade @samp{none} or @samp{none.gc}.
You can specify the grade in one of three ways: by setting the
@samp{MERCURY_DEFAULT_GRADE} environment variable, by adding a line
@vindex MERCURY_DEFAULT_GRADE
@samp{GRADE=@dots{}} to your @samp{Mmake} file, or by using the
@samp{--grade} option to @samp{mmc}.  (You will also need to install
those grades of the Mercury library, if you have not already done so.)

@item
If your compiler is particularly strict in
enforcing ANSI compliance, you may also need to compile the Mercury
code with @samp{--no-static-ground-terms}.

@end itemize

@c ----------------------------------------------------------------------------

@node Foreign language interface
@chapter Foreign language interface

The Mercury foreign language interfaces allows pragma foreign_proc to
specify multiple implementations (in different foreign programming
languages) for a procedure.

If the compiler generates code for a procedure using a back-end for which 
there are multiple applicable foreign languages, it will choose the
foreign language to use for each procedure according to a builtin ordering. 

If the language specified in a foreign_proc is not available for a
particular backend, it will be ignored. 

If there are no suitable foreign_proc clauses for a particular
procedure but there are Mercury clauses, they will be used instead.

@table @asis

@item @samp{C}
This is the default foreign language on all backends which compile to C
or assembler.
Only available on backends that compile to C or assembler.

@item @samp{C#}
Only available on backends that compile to IL.
This is the second preferred foreign language for IL code generation.

@item @samp{IL}
IL (or CIL) is the intermediate language of the .NET Common Language
Runtime.
Only available on backends that compile to IL.
This is the preferred foreign language for IL code generation.

@item @samp{Managed C++}
Managed Extensions for C++ is a language based on C++ that
provide support for writing .NET components, by adding extra
keywords and syntax.
Only available on backends that compile to IL.
This is the third preferred foreign language for IL code generation.


@end table

@c ----------------------------------------------------------------------------

@node Index
@unnumbered Index

@printindex cp

@c ----------------------------------------------------------------------------

@bye