Release 0.7 - Known Problems

The following is collected email of reported problems with release 0.7 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: bug with polymorphic abstract exported equivalence types
Date: Tue, 27 May 1997

The compiler generates incorrect code for the following program. The problem is that at the call to f/1 in module bar, f/1 has type `func(foo(T)) = int', and so it passes the type_info in r1 and the foo(T) (== int) in r2. But in the definition it has type `func(int) = int', so it just passes the int in r1. Similarly for the call to c/0.

:- module foo.
:- interface.
:- func f(foo(T)) = int.
:- type foo(T).
:- func c = foo(int).
:- implementation.
:- import_module int.
:- type foo(T) == int.

f(X) = X + 1.

c = 42.

:- module bar.
:- interface.
:- import_module io.
:- pred main(io__state::di, io__state::uo) is det.
:- implementation.
:- import_module foo.
main -->
	write(f(c)), nl.