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recursion - Prolog: Split list at integer in list of lists

I would like to split a list of words separated through integers into a list of lists.

Sample query and expected result:

?- separatewords([h,e,l,l,o,1,o,v,e,r,3,t,h,e,r,e], X).
X = [[h,e,l,l,o],[o,v,e,r],[t,h,e,r,e]].

The following things I already achieved: Splitting the list into one list before the first integer and one after the first integer:

Sample query with result:

?- take1word([h,e,l,l,o,1,o,v,e,r,3,t,h,e,r,e], X, Y).
X = [h,e,l,l,o], Y = [o,v,e,r,3,t,h,e,r,e].                 % OK

My code:

 take1word([H|T],[],T) :-
    integer(H).
 take1word([H|T],[H|Hs],Y) :-
    (  float(H), take1word(T,Hs,Y)
    ;  atom(H), take1word(T,Hs,Y)
    ).

For separating words my code is the following:

 separatewords([],[]).
 separatewords([H|T],L) :-  separatewords(T,[take1word([H|T],)|L]).

It only give me false as a result, but I don't know, what I am doing wrong.

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1 Answer

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by (71.8m points)

You have an issue with take1word/3: it will take a word if there is an integer in the list, but it will not take the last word. You need to add another base clause to it:

take1word([], [], []).
take1word([H|T],[],T) :- integer(H).
take1word([H|T],[H|Hs],Y) :- float(H), take1word(T,Hs,Y); atom(H), take1word(T,Hs,Y).

Now your separatewords/2 will work:

separatewords([],[]).
separatewords(L, [W|T]) :- take1word(L,W,R), separatewords(R,T).

Demo.


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