/* 

  DCG in Picat.

  From Nilsson & Matuszynski: "Logic, Programming and Prolog"
  Page 194f (Chapter 10: Logic and Grammar)



  This model was created by Hakan Kjellerstrand, hakank@gmail.com
  See also my Picat page: http://www.hakank.org/picat/

*/

import v3_utils.

main => go.

/*
  Picat> cl(dcg_sentence1),sentence(X,Y,[])
  X = s(john,runs)
  Y = [john,runs] ?;
  no

  Trace before first solution:
  Picat> trace
  Picat> cl(dcg_sentence1),sentence(X,Y,[])
   Call: (1) sentence(_13c20,_13c28,[]) ?r
   Call: (2) s(_14190,_14198) = _13c20
   Exit: (2) s(_14190,_14198) = s(_14190,_14198)
   Call: (3) np(_14190,_14ae8,_13c28,_14af8)
   Call: (4) var(_14190)
   Exit: (4) var(_14190)
   Call: (5) john = _14190
   Exit: (5) john = john
   Call: (6) singular(3) = _14ae8
   Exit: (6) singular(3) = singular(3)
   Call: (7) _13c28 = [john|_14af8]
   Exit: (7) [john|_14af8] = [john|_14af8]
?  Exit: (3) np(john,singular(3),[john|_14af8],_14af8)
   Call: (8) vp(_14198,singular(3),_14af8,[])
   Call: (9) runs = _14198
   Exit: (9) runs = runs
   Call: (10) singular(3) = singular(3)
   Exit: (10) singular(3) = singular(3)
   Call: (11) _14af8 = [runs]
   Exit: (11) [runs] = [runs]
?  Exit: (8) vp(runs,singular(3),[runs],[])
?  Exit: (1) sentence(s(john,runs),[john,runs],[])
X = s(john,runs)
Y = [john,runs] ?;

*/
go ?=>
  sentence(X,Y,[]),
  println(X=Y),
  fail,
  
  nl.
go => true.

%
% Variant: singular/1 -> singular/0, plural/1 -> plural/0
%
% Picat> sentence2(X,Y,[])
% X = s(john,runs)
% Y = [john,runs] ?;
% no
%
go2 ?=>
  sentence2(X,Y,[]),
  println(X=Y),
  fail,
  nl.
go2 => true.

%
% Original
%
sentence(s(X,Y)) --> np(X,N), vp(Y,N).
np(john,singular(3)) --> [john].
np(they,plural(3)) --> [they].
np(run,plural(_X)) --> [run].
vp(runs,singular(3)) --> [runs].

%
% skipping the numeric parameter to singular/1 and plural/1
%
sentence2(s(X,Y)) --> np2(X,N), vp2(Y,N).
np2(john,singular) --> [john].
np2(they,plural) --> [they].
np2(run,plural) --> [run].
vp2(runs,singular) --> [runs].