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prologmaplist

prolog gives Undefined procedure: atom_length/4

I'm trying to use maplist to filter a list of elements by limiting the length of each of the element, and here is what I tried

maplist(atom_length(2,X),[aa,bb,cc,asd],Result).
ERROR: apply:maplist_/3: Undefined procedure: atom_length/4
ERROR:   However, there are definitions for:
ERROR:         atom_length/2

I expect to get

Result = [aa,bb,cc]

A little help is required. Thanks.

Solution

  • A predicate that provides the functionality you require is findall_member/4. You can find a description and an implementation of this predicate in the Richard O'Keefe Prolog library proposal. For example:

    | ?- findall_member(Atom, [aa,bb,cc,asd], atom_length(Atom,2), Result).
Result = [aa, bb, cc]
yes

    The third argument of the findall_member/4 predicate is a test that is applied to each member of the list to filter the results.