Syntax error: Operator expected in prolog code

Question

I'm new to prolog .. i tried this code but got error and don't know why ?!

de(F,L,R):-
R=[F|L].

is that because rule must have a recursion ? the error is

ERROR: Syntax error: Operator expected

Answer 1

In your comment , you specify what you did wrong:

i tested it as de[a,[a,1,2,3],Z].

When you call a predicate, you use parenthesis ( (…) ), square brackets ( […] ) are used to construct lists. You thus should call the predicate with parenthesis:

?- defa,[a,1,2,3],Z.
Z = [a, a, 1, 2, 3].