/*******************************************************/
/*        Very simple PSG with no semantics            */
/*******************************************************/

:- multifile '--->'/2.       % Sicstus 3
:- op(1200,xfx,--->).        % Comma is op(1000,xfy,',').

/*******************************************************/
/*   Interface for bottom-up chart parser/generator    */
/*******************************************************/

string(Category, Category).

semantics(Category, [Category]).

lookup_word(Word, Category) :-
	(Category ---> [Word]), !.
lookup_word(Word, Category) :-
	write('unknown word: '),write(Word),nl,fail.
	
lookup_term(Category, Word, Category) :-
	(Category ---> [Word]).

empty_sem(empty, empty).

/*******************************************************/
/*           Interface for tree printer                */
/*******************************************************/

format_tree_node(Node, Functor) :-
	functor(Node, Functor, _).

portray(X) :- write(X).

/*******************************************************/
/*                    Grammar                          */
/*******************************************************/

s  ---> np, vp.

np ---> n.

np ---> d, n.

np ---> d, ap, n.

np ---> d, n, pp.

np ---> d, ap, n, pp.

vp ---> v.

vp ---> v, np.

vp ---> v, pp.

vp ---> v, np, pp.

pp ---> p, np.

ap ---> a.

ap ---> a, ap.

d ---> [the].

d ---> [some].

a ---> [big].

a ---> [brown].

a ---> [old].

n ---> [birds].

n ---> [fleas].

n ---> [dog].

n ---> [hunter].

v ---> [attack].

v ---> [ate].

v ---> [watched].

p ---> [for].

p ---> [beside].

p ---> [with].