First Attempt at Parsing

We assume that we will parse sentences converted to list format. That is the sentence ``the man ate the cake'' will be represented by the list [the man ate the cake].

We use append/3 to glue two lists together. The idea is that append/3 returns the result of gluing takes input as lists in the first and second argument positions and returns the result in the third position.

sentence(S):-



append(NP
VP
S)




noun_phrase(NP)




verb_phrase(VP).



noun_phrase(NP):-



append(Det
Noun
NP)




determiner(Det)




noun(Noun).



verb_phrase(VP):-



append(Verb
NP
VP)




verb(Verb)




noun_phrase(NP).



determiner([a]).



determiner([the]).



noun([man]).



noun([cake]).



verb([ate]).

?- sentence([the
man
ate
the cake]).



 append/3 succeeds with NP=[]
VP=[the
man
ate
the
cake]



 noun_phrase/1 fails



 append/3 succeeds with NP=[the]
VP=[man
ate
the
cake]



 noun_phrase/1 fails



 append/3 succeeds with NP=[the
man]
VP=[ate
the
cake]



 noun_phrase/1 succeeds



 ...



 verb_phrase/1 succeeds

This is all very well but the process of parsing with this method is heavily non deterministic.

Also it suffers from not being a very flexible way of expressing some situations. For example the problem of adjectives:

the quick fox

We might try to parse this kind of noun phrase with the extra clause:

noun_phrase(NP):-



append(Det
Bit
NP)




determiner(Det)




append(Adj
Noun
Bit)




adjective(Adj)




noun(Noun).