% file:  grammar-d.p
%        recognizer for X-bar verb phrases
%        - elimination of left recursion
%        - functionality of pp entities incorporated into grammar

% ---------- base productions ----------

sentence --> np(nom), vp, ['.'].
sentence --> [].

% np --> def_article, adj_list, noun.
np(nom) --> [she].
np(obj) --> [the], [space], [shuttle].

vp --> vbar.


% elimination of left-recursion
% vbar --> verb, vcomp.
% vbar --> vbar, vcomp.
vbar --> verb, vcomp(obj).
vbar --> verb, vcomp(obj), lvbar.

lvbar --> vcomp(X), { X \== obj }.
lvbar --> vcomp(X), { X \== obj }, lvbar.

vcomp(obj) --> np(obj).
vcomp(modifier) --> pp.
vcomp(modifier) --> [].

pp --> [at], [the], [airfield].
pp --> [on], [a], [friday].

verb --> [landed].