Re: Metainterpreter that prints call stack in case of failure.

From: Maurizio Colucci (look_at_in.signature)
Date: 07/02/04 

Date: Fri, 02 Jul 2004 09:19:54 GMT

Jan Wielemaker wrote:

>
> goal_expansion(Term, fcall(Term)) :-
> callable(Term),
> functor(Term, Name, Arity),
> must_succeed(Name/Arity).                % left to the user
>
> fcall(Goal) :-
> (   Goal
> *-> true
> ;   functor(Goal, Name, Arity),
> format(user_error, 'Unexpected failure of ~w/~d~n', [Name, Arity]),
> backtrace(10)                % number of parents displayed
> ).
>

Hello again :-)

I understood the mechanism, but there is a problem...

I tried calling run/0 with the input file:

must_succeed(run/0).

run:-
        dontFail([hello, world]).
dontFail(L):-
        member(hello, L),
        member(jack, L). % THIS will fail

goal_expansion(Term, fcall(Term)):-
        callable(Term),
        functor(Term, Name, Arity),
        must_succeed(Name/Arity).

fcall(Goal):-
        ( Goal ->
            true;
            ( functor(Goal, Name, Arity),
                format(user_error, 'Unexpected failure of ~w/~d~n', [Name, Arity]),
                backtrace(10))).

The output is the following:

Unexpected failure of run/0
   [8] prolog_stack:backtrace/1
                 at /usr/lib/pl-5.3.14/library/prolog_stack.pl:127
   [6] '$execute_goal2'/2 at /usr/lib/pl-5.3.14/boot/toplevel.pl:508
   [3] prolog/0 at /usr/lib/pl-5.3.14/boot/toplevel.pl:361
   [2] '$runtoplevel'/0 at /usr/lib/pl-5.3.14/boot/toplevel.pl:333
   [1] '$toplevel'/0 at /usr/lib/pl-5.3.14/boot/toplevel.pl:319

The problem is that the error message does not point me to the actual
subcall that failed:

  member(jack, [hello, world])

Furthermore, the backtrace starts from run/0, so it is not much useful. It
should start from member(jack, [hello,world])...

I am not sure what I should change to solve this... 

-- 
Best Regards,
Maurizio Colucci
Please remove the uppercase letters "S,P,A,M":
seSgPuAsMo.forever@tin.it