Re: DCG meta-predicate error

Hi Samer,

On 18/03/2014, at 18:11, Samer Abdallah <[email protected]> wrote:

> Hi,
> There appears to be a bug in the handling of meta-predicates that
> expect a DCG goal as an argument:
> 
> :- meta_predicate foo(//,?,?).
> 
> foo(G) --> phrase(G).
> 
> test --> foo({writeln(hello)}).
> 
> Using SWI v. 7.1.7 results in 
> Warning: The predicates below are not defined. If these are defined
> Warning: at runtime using assert/1, use :- dynamic Name/Arity.
> Warning: 
> Warning: {}/3, which is referenced by
> Warning:        /Users/samer/src/sandpit/prolog/test.pl:4: 1-st clause of test/2

I get:

$ swipl
% /Users/pmoura/.plrc compiled 0.00 sec, 2 clauses
Welcome to SWI-Prolog (Multi-threaded, 64 bits, Version 7.1.9-53-g30fa74b-DIRTY)
Copyright (c) 1990-2014 University of Amsterdam, VU Amsterdam
SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to redistribute it under certain conditions.
Please visit http://www.swi-prolog.org for details.

For help, use ?- help(Topic). or ?- apropos(Word).

?- [user].
:- meta_predicate foo(//,?,?).
|: 
|: foo(G) --> phrase(G).
|: 
|: test --> foo({writeln(hello)}).
|: % user://1 compiled 0.00 sec, 6 clauses
true.

?- listing(test/2).
test(A, B) :-
	foo({writeln(hello)}, A, B).

true.

?- listing(foo/3).
:- meta_predicate foo(//,?,?).

foo(A, B, C) :-
	phrase(A, B, C).

true.

?- phrase(test, []).
hello
true.

If I put your code in a file and consult it I get no warnings:

$ swipl
% /Users/pmoura/.plrc compiled 0.00 sec, 2 clauses
Welcome to SWI-Prolog (Multi-threaded, 64 bits, Version 7.1.9-53-g30fa74b-DIRTY)
Copyright (c) 1990-2014 University of Amsterdam, VU Amsterdam
SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to redistribute it under certain conditions.
Please visit http://www.swi-prolog.org for details.

For help, use ?- help(Topic). or ?- apropos(Word).

?- [samer].
% samer compiled 0.00 sec, 6 clauses
true.

Are you using a different SWI-Prolgo version or testing the code in a different way?

Cheers,

Paulo

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Paulo Moura
Logtalk developer

Email: <mailto:[email protected]>
Web:   <http://logtalk.org/>
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