Prolog lists (using stemming function)

Question

I know this is a very simple question but I seem to be having some problems.

I am trying to stem a list of words using porter_stem but I am getting an error:

Out of local stack

This is my code:

stemming([],[]).
stemming([H|T], A) :-
    stemming(T,Answer),
    porter_stem(H,S),
    append(Answer,S,A).

Basically the pseudocode for this is as follows:

for all items in list
    stem item
    add item to list2
    return list2

Can anyone please point me in the right direction please?

well, the first thing your stemming predicate does is to call stemming, it should be the last thing it does. — m09, Jan 06 '12 at 23:15
I can detail a normal recursion to you if you want, but did you try to use `maplist/3` or equivalent depending on your prolog implementation ? something like `maplist(porter_stem, List, Result).` would suffice. — m09, Jan 07 '12 at 00:32
you are appending each new element at the end of the accumulating list: `append(Answer,S,A)`. This is quadratic - it has to go over and over from the start of the list, building new copy and discarding old, only to add *one* element each time. You could try `stemming([H|T],[S|R]):- porter_stem(H,S),stemming(T,R)`. That's kind of re-implementing `maplist/2`. Also, see if [this approach](http://stackoverflow.com/questions/8869485/lazy-lists-in-prolog) help. — Will Ness, Aug 08 '12 at 22:25

score 1 · Accepted Answer · answered Jan 07 '12 at 20:09

1

Consider using maplist/3 or equivalent depending on your prolog implementation: something like maplist(porter_stem, List, Result). would suffice.

If you're interested in learning how to build a proper recursion, post a comment and I'll try to expand my answer :)

answered Jan 07 '12 at 20:09

m09

Thank you so much! If I could understand what was wrong with the code I pasted, I would be everso grateful. – Lilz Jan 07 '12 at 20:27

1 Answers1