% Example of abduction in CHR Grammars by Henning Christiansen

%:- compile(chrg).


:- chrg_option(show_rules,on).

:- chrg_abducible food_for/2, categ_of/2, cannibal/1.
:- chrg_symbols name/1, verb/1, sentence/1, category/1.

/***** test query

parse([garfield,eats,mickey, tom,eats,jerry, jerry,is,mouse,
       tom,is,cat, mickey,is,mouse]).

********/

%%% Integrity constraints

categ_of(N,C1), categ_of(N,C2) ==> C1=C2.
food_for(C1,C), food_for(C2,C) ==> C1=C2.
food_for(C,C) ==> cannibal(C).

%%% Grammar rules

verb(is) -\ [X] <:> category(X).

[tom]     <:> name(tom).
[jerry]   <:> name(jerry).
[garfield]  <:> name(garfield).
[mickey]  <:> name(mickey).
[is]      <:> verb(is).
[eats]    <:> verb(eats).

name(N), verb(is), category(T) <:>
   {categ_of(N,T)},
   sentence(is(N,T)).

name(N1), verb(eats), name(N2) <:>
    {categ_of(N1,T1), categ_of(N2,T2), food_for(T1,T2)},
    sentence(eats(N1,N2)).



end_of_CHRG_source.