mercury/BUGS

Bug reports should be sent to mercury-bugs@cs.mu.oz.au.
If you're reporting more than one bug, please use separate emails
for each bug.  Please include all the relevant information,
including which version of Mercury you're using, what operating
system you're using, and a complete source file that
demonstrates the problem.  (If it's something that only shows
up in multi-module programs, send a shar archive or uuencoded
tar archive containing your source files.)  Please try to ensure
that bug reports contain all the information that we need to be
able to reproduce the problem.  Make sure that all bug reports are
fully self-contained.

Below is a list of the known outstanding bugs.
We'll try to record any other bugs that are discovered in 0.6
on our WWW page <http://www.cs.mu.oz.au/mercury>.
See also the LIMITATIONS file.

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Subject: bug report - Inf and NaN
Date: Wed, 4 Oct 1995 02:48:19 +1000 (EST)

The following module causes an "undefined variable Inf" error in the
generated C code, because 1E400 == Infinity, which gets printed as `Inf'.

:- module hello.
:- interface.
:- import_module io.

:- pred main(io__state::di, io__state::uo) is det.

:- implementation.

main -->
	io__write_float(1E400),
	io__write_string("\n").

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Subject: bug with no_tag tags and partially instantiated data structures
Date: Fri, 19 Apr 1996 19:47:18 +1000 (EST)

> :- module bug.
> :- interface.
> :- type foo ---> foo(int).
> :- pred bug(foo::out) is det.
> :- implementation.
> bug(Y) :-
> 	Y = foo(_),
> 	Z = 42,
> 	Y = foo(Z).

This gives the error "code_exprn__cache_exprn: existing definition of var".

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Subject: problem with lookup_switch
Date: Sun, 5 May 1996 16:00:17 +1000 (EST)

I think there's a bug in lookup_switch.  What happens if you try to
cross-compile for a 64 bit architecture on a 32 bit machine?  I think
it tries to compute the 64-bit bitmap table entries using 32-bit ints,
which overflow.

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Subject: map__lookup failed in profiler
Date: Tue, 7 May 1996 11:58:08 +1000 (EST)

When profiling programs that have been compiled on the Alpha using
shared libraries, the profiler will abort with a "Software Error:
map__lookup failed" message.  The work-around is to link with
`--static'.

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Subject: nit in error msg
Date: Thu, 16 May 1996 10:25:42 +1000 (EST)

Here's another small error in an error message.  If you comment out
the [] clause for the functions car/1 or cdr/1, you get this message:

fntest.m:023: In `car(in) = out':
fntest.m:023:   Error: determinism declaration not satisfied.
fntest.m:023:   Declared `det', inferred `semidet'.
fntest.m:023:   in argument 1 of clause head:
fntest.m:023:   unification of `HeadVar__1' and `[X | V_4]' can fail.

It says Declared `det', inferred `semidet', but I never declared it at
all.  It's a bit misleading.  Certainly not a major problem, and the
later part of the message makes it quite clear what the problem is,
but I thought I'd point it out to you before I forgot it.

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Subject: obscure bug with identical function and constructor
Date: Sat, 25 May 1996 19:24:12 +1000 (EST)

% This test case shows up an obscure bug in the compiler.
% The compiler reports spurious mode errors in the compiler-generated
% unification/compare/index predicates.
% It's not quite clear whether or not this should be legal,
% but the compiler ought to at least report a better error message.
% If you write obfuscated code like this, you really deserve
% what you get, but I guess we should fix the bug someday anyway...

:- module nasty_func_test.
:- type foo ---> f(int) ; g.

:- func f(int) = foo.
f(_) = g.

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Subject: missed mode error
Date: Tue, 28 May 1996 02:27:34 +1000 (EST)

Another one for the bug report file:

The goal `some [X, Y] X \= Y' should be a mode error,
but the current mode checker doesn't report an error.
Instead, the compiler goes on to generate code which gives
the wrong answer.  For example, the following program prints out `no'.
The same problem also occurs with `some [X, Y] (X = Y -> fail ; true)'.

:- module bug.
:- interface.
:- import_module io.

:- pred main(io__state::di, io__state::uo) is det.

:- implementation.

main --> 
	( { p } -> io__write_string("yes\n") ; io__write_string("no\n") ).

:- pred p is semidet.
p :-
	some [X, Y] X \= Y.

The bug occurs only when the variables being unified inside a negated
context are not live, i.e. when it is the last occurrence of those variables.

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Subject: bug with PC values on Alpha
Date: Wed, 12 Jun 1996 15:45:59 +1000

On the alpha, if the Mercury runtime catches a signal, it
sometimes prints out the wrong value for the PC.

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Subject: inference bug
Date: Mon, 24 Jun 1996 15:48:12 +1000 (EST)

The compiler sometimes aborts with a map_lookup failed
after mode inference finds some mode errors.

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Subject: relation.m
Date: Mon, 29 Jul 1996 16:34:46 +1000 (EST)

relation__atsort does not correctly compute the topological sort for
disconnected cliques.  These cliques do not appear in the output list.

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Subject: cc_nondet and cc_multi disjunctions

The code generator aborts with "Software Error: map__lookup failed"
when compiling certain code involving disjunctions with output
variables that occur in single-solution contexts, e.g.

:- pred main(io__state::di, io__state::uo) is cc_multi.

main --> io__read_line(Res),
	( { Res = ok(['y']) }, io__write_string("Yes\n")
	; { Res = ok(['n']) }, io__write_string("No\n")
	; io__write_string("Huh?\n")
	).

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