Prolog 运算符预期错误

Question

我搜索了 Prolog Operator expected error questions at stack overflow，但是我无法确定我遇到的错误：

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

代码很简单：

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).

Answer 1

这确实是这个问题的重复：Prolog map procedure that applies predicate to list elements

但我会咬人。你可以像建议的那样简单地说：

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

Prolog 运算符预期错误

Prolog Operator Expected Error

prolog

syntax-error

meta-predicate