Prolog Operator Expected Error

Question

I have searched Prolog Operator expected error questions at stack overflow, however I can't identify the error I am getting :

4:26: Syntax error: Operator expected
% 3.pl compiled 0.00 sec, 3 clauses

The code is simple:

inc(N,R) :-
  R is N + 1. % Simple code to increment a number.

mapcar( F , []    , []     ).  % Base case 
mapcar( F , [H|T] ,[RH|RT] ) :- % Increment head and put it in Result Head and Recurse for Tail
  F(H,RH),
  mapcar(F,T,RT).

`F(H,RH)` is invalid. What do you intend with that expression? — lurker, Jan 15 '15 at 15:49
instead of F(H,RH) use call(F,H,RH) or Pred =.. [F,H,RH], call(Pred) — CapelliC, Jan 15 '15 at 15:50
@CapelliC I changed F to f and my program compiled without error, but it is not working correctly. It is expected to increment all elelents in the list. — ed bale, Jan 15 '15 at 15:55
@edbale that won't fix it, you should use `call` as CapelliC suggest. — VHarisop, Jan 15 '15 at 15:55

score 1 · Accepted Answer · edited May 23 '17 at 11:57

1

This is really a duplicate of this question: Prolog map procedure that applies predicate to list elements

But I'll bite. You cansimply say, as was suggested:

map( _ , []     , []     ) .
map( G , [X|Xs] , [Y|Ys] ) :-
  call(G,X,Y)  ,
  map(G,Xs,Ys) .

edited May 23 '17 at 11:57

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answered Jan 15 '15 at 18:49

Nicholas Carey

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Prolog Operator Expected Error

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