% Grammar 4.4 A BH-GRN grammar with tree building arguments

:- op(1200, xfx, ===>).
:- op(1200, xfx, --->).

s(s(NP, VP)) ---> [np(NP), vp(VP)].
vp(vp(V)) ---> [v(V)].
vp(vp(V, NP)) ---> [v(V), np(NP)].

np(np(toby)) ===> [toby].
np(np(scotch)) ===> [scotch].
np(np(drinks)) ===> [drinks].
v(v(drinks)) ===> [drinks].

% See page 113 last paragraph for discussion of the following 

(LHS ---> RHS, no_code) :- (LHS ---> RHS).
(LHS ===> RHS, no_code) :- (LHS ===> RHS).