mercury/compiler/notes/CODING_STANDARDS

Documentation
-------------

Each module should contain header comments which state
the module's name, main author(s), and purpose, and
give an overview of what the module does, what are the
major algorithms and data structures it uses, etc.

Each type or predicate that is exported from a module should have
sufficient documentation that it can be understood without reference
to the module's implementation section.

Each predicate other than trivial access predicates should have
a short comment describing what the predicate is supposed to do,
and what the meaning of the arguments is.

There should be a comment for each field of a structure saying
what the field represents.

Any user-visible changes such as new compiler options or new
features should be documented in appropriate section
of the Mercury documentation (usually the Mercury User's Guide
and/or the Mercury Reference Manual).  Any major new features
should be documented in the NEWS file, as should even small
changes to the library interface, or anything else that might
cause anyone's existing code to break.

Any new compiler modules or other major design changes should
be documented in `compiler/notes/COMPILER_DESIGN'.

Naming
------

Variables should always be given meaningful names,
unless they are irrelevant to the code in question.
For example, it is OK to use single-character names
in an access predicate which just sets a single
field of a structure, such as

	bar_set_foo(Foo, bar(A, B, C, _, E), bar(A, B, C, Foo, E)).

Variables which represent different states or different versions
of the same entity should be named Foo0, Foo1, Foo2, ..., Foo.

Predicates which get or set a field of a structure or ADT should
be named bar_get_foo and bar_set_foo respectively, where bar
is the name of the structure or ADT and foo is the name of the field.


Coding
------

Your code should make as much reuse of existing code as possible.
"cut-and-paste" style reuse is highly discouraged.

Your code should be efficient.  Performance is a quite
serious issue for the Mercury compiler.

No fixed limits please! 
(If you really must have a fixed limit, include detailed documentation
explaining why it was so hard to avoid.)


Error Handling
--------------

Code should check for both erroneous inputs from the user and also
invalid data being passed from other parts of the Mercury compiler.
You should also always check to make sure that the routines that you
call have succeed; make sure you don't silently ignore failures.  (This
last point almost goes without saying in Mercury, but is particularly
important to bear in mind if you are writing any C code or shell
scripts, or if you are interfacing with the OS.)

Calls to error/1 should always indicate an internal software error, not
merely incorrect inputs from the user, or failure of some library routine
or system call.

Error messages should follow a consistent format.  For compiler error
messages, each line should start with the source file name and line
line number in "%s:%03d: " format (but use prog_out__write_context --
we may want to change this format later, e.g. to include column
numbers).  Compiler error messages should be complete sentences; they
should start with a capital letter and end in a full stop.  For error
messages that are spread over more than one line (as are most of them),
the second and subsequent lines should be indented two spaces.  If the
`--verbose-errors' option was set, you should print out additional text
explaining in detail what the error message means and what the likely
causes are.

Error messages from the runtime system should begin with the text
"Mercury Runtime:", preferably by using the fatal_error() routine.

If a system call or C library function that sets errno fails, the
error message should be printed with perror() or should contain
strerror(errno).  If it was a function manipulating some file, the
error message should include the filename.


Layout
------
Code should be indented consistently.
Tabs should be every 8 spaces.
Indentation should be one tab per level of indentation.
except for highly intended code which may be
indented at 4 spaces per level of indentation.
Each line should not extend beyond 80 characters,
unless this is necessary due to the use of long string literals.
If-then-elses should always be parenthesized
(except that an if-then-else that occurs as the else
part of another if-then-else doesn't need to be parenthesized).
The condition of an if-then-else can either be on the same
line as the opening parenthesis and the `->', or it can
be on a line of its own.

Sections of code that are conceptually separate should be
separated with dashed lines:

%---------------------------------------------------------------------------%


Testing
-------

Every change should be tested before being committed.
The level of testing required depends on the nature of the change.
If this change fixes an existing bug, and is not likely to introduce
any new bugs, then just compiling it and running some tests
by hand is sufficient.  If the change might break the compiler,
you should run a bootstrap check (using the `bootcheck' script)
before committing.  If the change means that old versions of
the compiler will not be able to compile the new version of the
compiler, you must notify all the other Mercury developers.

In addition to testing before a change is committed, you need to make
sure that the code will not get broken in the future by adding tests to
the test suite.  Every time you add a new feature, you should add some
test cases for that new feature to the test suite.  Every time you fix
a bug, you should add a regression test to the test suite.


Committing changes
------------------

Before committing a change, you should get someone else to review your
changes.  Normally this should be done by sending the output of `cvs
diff -u' to fjh@cs.mu.oz.au, together with a description of the changes
for the CVS log.  The description should state why the changes were
made, not just what the changes were.  If you have added any new files
or directories, you *must* check the group-id and permissions of the
newly created files or directories in the CVS repository.  Files should
be readable by group mercury and directories should be both readable
and writeable by group mercury.