Question

Lets say that I would like to construct a list (L2) by appending elements of another list (L) one by one. The result should be exactly the same as the input.
This task is silly, but it’ll help me understand how to recurse through a list and remove certain elements.

I have put together the following code:

create(L, L2) :- (\+ (L == []) -> L=[H|T], append([H], create(T, L2), L2);[]).

calling it by

create([1,2,3,4], L2)

returns

L2 = [1|create([2,3,4], **)\.

which is not a desired result.

Answer 1

You say that you want to understand how prolog works so I’ll not give you a full solution but a hint.

Functions in prolog do not return values, they just create bindings.

When you say

append([H], create(T, L2), L2);[]).

you are trying to use a return value.

Try to have append create bindings that you use in the recursive call.