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WHPARSER.PL
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1991-10-31
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/* From the book PROLOG PROGRAMMING IN DEPTH
by Michael A. Covington, Donald Nute, and Andre Vellino.
Copyright 1988 Scott, Foresman & Co.
Non-commercial distribution of this file is permitted. */
/* Modified for Quintus Prolog by Andreas Siebert */
/* WHPARSER.PL */
/* Parser that handles WH-questions as well as statements.
For simplicity, we neglect morphology. */
/* Each phrase that can contain a WH-word has 3 arguments:
(1) List of WH-words found before starting to
parse this constituent;
(2) List of WH-words still available after
parsing this constituent;
(3) Structure built while parsing this
constituent (as in STRUCTUR.PL). */
/* Queries will use built-in predicate phrase/2 */
sentence(X,Z,sentence(NP,VP)) --> /* Sentence that does not */
noun_phrase(X,Y,NP), /* begin with a WH-word, */
verb_phrase(Y,Z,VP). /* but may be embedded in */
/* a sentence that does */
sentence(X,Z,sentence(NP,VP)) -->
wh_word(W), /* Sentence begins with WH-word. */
[did], /* Put the WH-word on the list, */
noun_phrase([W|X],Y,NP), /* absorb "did," and continue. */
verb_phrase(Y,Z,VP).
noun_phrase(X,X,noun_phrase(D,N)) -->
determiner(D), /* Ordinary NP that does */
noun(N). /* not use saved WH-word */
noun_phrase([X|Tail],Tail,noun_phrase(X)) --> [].
/* Missing NP supplied by picking a */
/* stored WH-word off the list */
verb_phrase(X,Z,verb_phrase(V,NP)) -->
verb(V),
noun_phrase(X,Z,NP).
verb_phrase(X,Z,verb_phrase(V,S)) -->
verb(V),
sentence(X,Z,S).
determiner(determiner(a)) --> [a].
determiner(determiner(the)) --> [the].
noun(noun(dog)) --> [dog].
noun(noun(cat)) --> [cat].
noun(noun(boy)) --> [boy].
noun(noun(girl)) --> [girl].
/* Two forms of every verb:
"The boy saw the cat" vs. "Did the boy see the cat?" */
verb(verb(chased)) --> [chased];[chase].
verb(verb(saw)) --> [saw];[see].
verb(verb(said)) --> [said];[say].
verb(verb(believed)) --> [believed];[believe].
wh_word(who) --> [who].
wh_word(what) --> [what].
/* Sample queries */
demo1 :- phrase(sentence([],[],Structure),
[who,did,the,boy,believe,the,girl,saw]),
write(Structure),
nl.
demo2 :- phrase(sentence([],[],Structure),
[who,did,the,boy,believe,saw,the,girl]),
write(Structure),
nl.