DCG в SWI-Prolog-е

% top([is, it, true, that, mark, hamill, acts, in, star, wars, iv]).
 
top(Sentence) :-
  yesno(Query, Sentence, []),                  
  Query,                                      
  write("Yes, that's true").
 
yesno(Sem) --> [is, it, true, that], statement(_^_^[Sem]).
 
statement(Subj^Obj^Sem) -->
    noun_phrase(Subj),
    verb_phrase(Subj^Obj^Sem).
 
noun_phrase(Sem) --> proper_noun(Sem).
 
verb_phrase(Subj^Obj^Sem) -->
   verb(Subj^Obj^Sem),
   noun_phrase(Obj).
 
verb(X^Y^[acts_in(X,Y)]) --> [acts, in].
 
actor(mark_hamill).
acts_in(mark_hamill, star_wars4).
proper_noun(mark_hamill) --> [mark, hamill].
proper_noun(star_wars4) --> [star, wars, iv].

% top([did, mark, hamill, play, spock]). 
 
top(Sentence) :-
    yesno(Query, Sentence, []),                  
    Query,                                       
    write("Yes, that's true").
 
yesno(Sem) --> [did], statement([Sem]^_^_).
 
statement(Subj^Obj^Sem) -->
    noun_phrase(Subj),
    verb(Subj^Obj^Sem).
 
noun_phrase(Sem) --> proper_noun(Sem).
 
verb(X^Y^playing(X,Y)) --> [play].
 
actor(mark_hamill).
acts_in(mark_hamill, star_wars4).
playing(mark_hamill, spock).
proper_noun(mark_hamill) --> [mark, hamill].
proper_noun(star_wars4) --> [star, wars, iv].