[mercury-users] compilation problem, all, some

[Zoltan Somogyi]

On 16-Jul-2004, Maurizio Colucci <seguso.forever at tin.it> wrote:
> % Intuitively, a verb V is visible if for all O in SelectedObjects 
> % there is a predicate P in V's requirements such that P(O).
> 
> the_verb_is_visible(V, SelectedObjs):-
>     verb_get_requirements(V, Reqs),
>     forall( member(O, SelectedObjs),
>             ( member(P, Reqs),
>               call(P, O))).

The transliteration of the comment is the following:

the_verb_is_visible(V, SelectedObjs) :-
	verb_get_requirements(V, Reqs),
	all [O] (
		member(O, SelectedObjs)
	=>
		member(P, Reqs),
		call(P, O)
	).

> On Suse 9.1, with gcc 3.3.3, if  I try to compile "hello world" with the 
> stable release (0.11.0), I get the following errors:
> > cd /dat/pub/src/by-mau/tests/mercury/
> > mmc main.m
> > main_init.o(.text+0x133): In function `mercury_init':
> > : undefined reference to `<predicate 'main'/2 mode 0>'
> > /usr/local/mercury-0.11.0/lib/mercury/lib/asm_fast.gc/i686-pc-linux-gnu/libmer_std.a(lexer.o)
> (.text+0xcd44): In function `<predicate 'lexer:get_float_decimals'/4 mode 
> 0>':
> > : undefined reference to `__ctype_b'

This looks like an incompatibility between the system's ctype.h header file
and the C standard library. What happens if you #include <ctype.h> in a simple
C program and use e.g. isalpha()?

>  If I try to compile hello world with the _unstable_ rpm, I get these errors:
> 
> mmc main.m
> main_init.c: In function `mercury_init':
> main_init.c:776: warning: dereferencing type-punned pointer will break 
> strict-aliasing rules
> main_init.c:778: warning: dereferencing type-punned pointer will break 
> strict-aliasing rules
> main_init.c:780: warning: dereferencing type-punned pointer will break 
> strict-aliasing rules
> main_init.c:782: warning: dereferencing type-punned pointer will break 
> strict-aliasing rules
> main_init.c:784: warning: dereferencing type-punned pointer will break 
> strict-aliasing rules
> main_init.c:786: warning: dereferencing type-punned pointer will break 
> strict-aliasing rules
> main_init.o(.text+0x179): In function `mercury_init':
> : undefined reference to `<predicate 'main'/2 mode 0>'

You get these errors because gcc 3.4 assumes -fstrict-aliasing by default
at -O2, but the code generated by the Mercury compiler doesn't abide by
the rules this requires. (This is by design; we use C as portable assembler.)
You can ignore all such errors from code generated by the Mercury compiler
by specifying --fno-strict-aliasing. I committed a patch last week to detect
the presence of this flag, and have mgnuc turn it on by default if needed.

Zoltan.
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