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GNU Prolog simple program doesn't work as expected

EDIT : I've just compiled gprolog from sources.

It works fine. The version 1.4.5 in the Debian repo is bugged.

It's my first program in GNU Prolog (gprolog) without any success. :-(

I found these exercises in a Prolog tutorial.

GNU Prolog 1.4.5 (64 bits)
Compiled Feb  5 2017, 10:30:08 with gcc
By Daniel Diaz
Copyright (C) 1999-2016 Daniel Diaz
compiling /home/aubin/Dev/Prolog/overview/parents.prolog for byte code...
/home/aubin/Dev/Prolog/overview/parents.prolog compiled, 39 lines read - 2555 bytes written, 3 ms
| ?- grandPere( GrandPere, eve ).
uncaught exception: error(existence_error(procedure,pere/0),grandPere/0)
| ?- parent( PereOuMere, eve ).
uncaught exception: error(existence_error(procedure,pere/0),parent/0)
| ?- parents( Pere, Mere, eve).

no
| ?- parents( aubin, muriel, X ).

no
| ?- frere_ou_soeur( X, aubin ).

no
| ?- listing.

% file: /home/aubin/Dev/Prolog/overview/parents.prolog

pere(joseph, michel).
pere(michel, aubin).
pere(michel, brigitte).
pere(michel, sylvie).
pere(alain, muriel).
pere(aubin, eve).

mere(colette, muriel).
mere(muriel, eve).

grandPere(A, B) :-
    pere(A, C),
    pere(C, B).

parent(A, B) :-
    pere(A, B).
parent(A, B) :-
    mere(A, B).

frere_ou_soeur(A, B) :-
    A \= B,
    parent(C, A),
    parent(C, B).

parents(A, B, C) :-
    A \= B,
    A \= C,
    B \= C,
    pere(A, C),
    mere(B, C).

yes

The expected answers are :

grandPere( GrandPere, eve ). ==> GrandPere = michel
parent( PereOuMere, eve ).   ==> PereOuMere = aubin, PereOuMere = muriel
parents( Pere, Mere, eve).   ==> Pere = aubin, Mere = muriel
parents( aubin, muriel, X ). ==> Enfant = eve
frere_ou_soeur( X, aubin ).  ==> X = brigitte, X = sylvie

First line of the source is:

#!/usr/bin/gprolog --consult-file

And the invocation is:

$ gprolog --consult-file parents.prolog 
GNU Prolog 1.4.5 (64 bits)
Compiled Feb  5 2017, 10:30:08 with gcc
By Daniel Diaz
Copyright (C) 1999-2016 Daniel Diaz
compiling /home/aubin/Dev/Prolog/overview/parents.prolog for byte code...
/home/aubin/Dev/Prolog/overview/parents.prolog compiled, 39 lines read - 2555 bytes written, 3 ms
| ?- grandPere( GrandPere, eve ).
uncaught exception: error(existence_error(procedure,pere/0),grandPere/0)
| ?-
Solution

  • It seems that invoked with a file name, gprolog validates it but does not load its content into the interpreter. In order to load the file content you have to use the --consult-file command line option:

    $ gprolog --consult-file parents.prolog
GNU Prolog 1.4.5 (64 bits)
Compiled Jul 14 2018, 19:58:18 with clang
By Daniel Diaz
Copyright (C) 1999-2018 Daniel Diaz
compiling /private/tmp/parents.prolog for byte code...
/private/tmp/parents.prolog compiled, 31 lines read - 2474 bytes written, 9 ms
| ?- mere(muriel, eve).

yes
| ?- grandPere( GrandPere, eve ).

GrandPere = michel ?

yes

    Read about the usage of gprolog on its documentation page.