Release 0.8 - Known Problems

The following is collected email of reported problems with release 0.8 of the Mercury distribution. Included, where possible, are patches.

Subject: bug report - Inf and NaN
Date: Wed, 4 Oct 1995

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 -->

Subject: map__lookup failed in profiler
Date: Tue, 7 May 1996

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'.

This is actually due to a bug in the Alpha shared library mechanism, which does not conform to the ANSI C standard. So there is not much we can do about this one.

Subject: nit in error msg
Date: Thu, 16 May 1996

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.

Subject: missed mode error
Date: Tue, 28 May 1996

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.

Subject: bug with PC values on Alpha
Date: Wed, 12 Jun 1996

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

Subject: inter-module optimization and abstract exported equivalence types.
Date: Thu, 19 Feb 1998

In some cases the compiler reports spurious ambiguity errors when compiling with `--intermodule-optimization'. This is due to the definition of abstract exported equivalence types being made visible by inter-module optimization. In this example, with `--intermodule-optimization' the compiler sees the declaration `:- type var == int' from term.m and then cannot determine whether `Elem' has type `int' or `pair(int)'. The work-around is to add an explicit type qualification.

:- module foo.
:- interface.
:- import_module list, term.
:- pred test(list(var)::in) is det.
:- implementation.
:- import_module int, std_util.

test(Args0) :-
	MakeIndex =
		lambda([Elem0::in, Elem::out, Index0::in, Index::out] is det, (
			Elem = Elem0 - Index0,
			Index is Index0 + 1
	list__map_foldl(MakeIndex, Args0, _, 0, _).