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).