Left corner parser in prolog for simple sentence

Question

I am trying to build a top left parser in prolog for the sentence "The little pigs were safe inside" and I am trying to figure out where I went wrong in my code. (Note: I'm a beginner in prolog and the code I wrote is based on a working example I had)

Can anybody point me in the right direction on this and maybe shine some light on it?

Code:

% The little pigs were safe inside.

% ------------------------------------------------  TERMINALS  ------------------------------------------------

leaf(determiner) --> [the].

leaf(adjective) --> [little].

leaf(adjective) --> [safe].

leaf(noun) --> [pigs].

leaf(verb) --> [were].

leaf(adverb) --> [inside].

% ------------------------------------------------  NON-TERMINALS   ------------------------------------------------

lcd(noun_phrase,sentence):-!.
lcd(determiner,noun_phrase):-!.
lcd(adjective,adjective_phrase):-!.
lcd(adverb,adjective_phrase):-!.
lcd(verb,verb_phrase):-!.
lc(X,X):-!.
lc(X,Y):-lcd(X,Y),!.
lc(X,Y):-lcd(X,Z),lc(Z,Y).

% ------------------------------------------------  RULES   ------------------------------------------------

parse(Nterm,As,[W0|W1],Wn):-
    leaf(Pterm,[W0|W1],W1),
    lc(Pterm,Nterm),
    Ap=..[Pterm,W0],
    P=..[Pterm,Nterm,Ap,As,W1,Wn],
    call(P).

noun_phrase(Nt,NP,As)-->{lc(sentence,Nt)},parse(verb_phrase, VP),sentence(Nt,sentence(NP,VP),As),!.
noun_phrase(noun_phrase,E,E)-->[].

determiner(Nt,D,As)-->{lc(noun_phrase,Nt)},parse(adjective_phrase,N),noun_phrase(Nt,noun_phrase(D,N),As).

adjective(Nt,A,As)-->{lc(adjective_phrase,Nt)},parse(adjective_phrase,N),adjective_phrase(Nt,adjective_phrase(A,N),As).

adverb(Nt,A,As)-->{lc(adjective_phrase,Nt)},parse(adjective_phrase,N),adjective_phrase(Nt,adjective_phrase(A,N),As).

noun(Nt,N,As)-->{lc(adjective_phrase,Nt)},adjective_phrase(Nt,adjective_phrase(N),As).
adjective_phrase(adjective_phrase,A,A)-->[].

verb(Nt,V,As)-->{lc(verb_phrase,Nt)},parse(noun_phrase,N),verb_phrase(Nt,verb_phrase(V,N),As).
verb(Nt,V,As)-->{lc(verb_phrase,Nt)},verb_phrase(Nt,verb_phrase(V),As).
verb_phrase(verb_phrase,A,A)-->[].
sentence(s,A,A)-->[].

test(S,A):-parse(S,A,[the, little, pigs, were, safe, inside],[]).

Test trace:

trace,test(S,A).
Call: (9) test(_4648, _4650) ? creep
Call: (10) parse(s, _4650, [the, little, pigs, were, safe, inside], []) ? creep
Call: (11) leaf(_5024, [the, little, pigs, were, safe, inside], [little, pigs, were, safe, inside]) ? creep
Exit: (11) leaf(determiner, [the, little, pigs, were, safe, inside], [little, pigs, were, safe, inside]) ? creep
Call: (11) lc(determiner, s) ? creep
Call: (12) lcd(determiner, s) ? creep
Fail: (12) lcd(determiner, s) ? creep
Redo: (11) lc(determiner, s) ? creep
Call: (12) lcd(determiner, _5026) ? creep
Exit: (12) lcd(determiner, noun_phrase) ? creep
Call: (12) lc(noun_phrase, s) ? creep
Call: (13) lcd(noun_phrase, s) ? creep
Fail: (13) lcd(noun_phrase, s) ? creep
Redo: (12) lc(noun_phrase, s) ? creep
Call: (13) lcd(noun_phrase, _5026) ? creep
Exit: (13) lcd(noun_phrase, sentence) ? creep
Call: (13) lc(sentence, s) ? creep
Call: (14) lcd(sentence, s) ? creep
Fail: (14) lcd(sentence, s) ? creep
Redo: (13) lc(sentence, s) ? creep
Call: (14) lcd(sentence, _5026) ? creep
Fail: (14) lcd(sentence, _5026) ? creep
Fail: (13) lc(sentence, s) ? creep
Fail: (12) lc(noun_phrase, s) ? creep
Fail: (11) lc(determiner, s) ? creep
Redo: (11) leaf(_5024, [the, little, pigs, were, safe, inside], [little, pigs, were, safe, inside]) ? creep
Fail: (11) leaf(_5024, [the, little, pigs, were, safe, inside], [little, pigs, were, safe, inside]) ? creep
Fail: (10) parse(s, _4650, [the, little, pigs, were, safe, inside], []) ? creep
Fail: (9) test(_4648, _4650) ? creep
false.

The expected output for this grammar when running the test should be something like:

S = [the, little, pigs, were, safe, inside],A = s(np(d(the), adjp(adj(little), n(pigs))), vp(v(were), adjp(adj(safe), adv(inside)))) .

Answer 1

For anyone who might need this later on. Only a few fixes were needed to make this work. Compare the two programs to find the mistakes :)

Solution

% The little pigs were safe inside.

% ------------------------------------------------  TERMINALS   ------------------------------------------------

leaf(determiner) --> [the].

leaf(adjective) --> [little].
leaf(adjective) --> [safe].

leaf(noun) --> [pigs].

leaf(verb) --> [were].

leaf(adverb) --> [inside].

% ------------------------------------------------  NON-TERMINALS   ------------------------------------------------

lcd(noun_phrase,sentence):-!.
lcd(determiner,noun_phrase):-!.
lcd(verb,verb_phrase):-!.
lcd(adjective,adjective_phrase):-!.

lc(X,X):-!.
lc(X,Y):-lcd(X,Y),!.
lc(X,Y):-lcd(X,Z),lc(Z,Y).

parse(Nterm,As,[W0|W1],Wn):-
    leaf(Pterm,[W0|W1],W1),
    lc(Pterm,Nterm),
    Ap=..[Pterm,W0],
    P=..[Pterm,Nterm,Ap,As,W1,Wn],
    call(P).

% ------------------------------------------------  RULES   ------------------------------------------------

noun_phrase(Nt,NP,As)-->{lc(sentence,Nt)},parse(verb_phrase, VP),sentence(Nt,sentence(NP,VP),As),!.
noun_phrase(noun_phrase,E,E)-->[].

determiner(Nt,D,As)-->{lc(noun_phrase,Nt)},parse(adjective_phrase,N),noun_phrase(Nt,noun_phrase(D,N),As).
adjective_phrase(adjective_phrase,A,A)-->[].

verb(Nt,V,As)-->{lc(verb_phrase,Nt)},parse(adjective_phrase,N),verb_phrase(Nt,verb_phrase(V,N),As).
verb_phrase(verb_phrase,A,A)-->[].

adjective(Nt,A,As)-->{lc(adjective_phrase,Nt)},parse(noun,N),adjective_phrase(Nt,adjective_phrase(A,N),As).
noun(noun,A,A)-->[].

adjective(Nt,A,As)-->{lc(adjective_phrase,Nt)},parse(adverb,Adv),adjective_phrase(Nt,adjective_phrase(A,Adv),As).
adverb(adverb,A,A)-->[].

sentence(sentence,A,A)-->[].

% ------------------------------------------------  TEST   ------------------------------------------------

test(sentence,A):-parse(sentence,A,[the, little, pigs, were, safe, inside],[]).
test1(sentence,A):-parse(sentence,A,[the, little, pigs],[]).