Prolog, building list with conditional clauses

Question

I need to do this homework assignment using prolog (SWI-flavor) and cant get my head around some things.

For example, if i want to iterate through a list and add it

Answer 1

If I understand correctly, then what you need is a predicate like include/3:

include(:Goal, +List1, ?List2)
    Filter elements for which Goal succeeds. True if List2 contains
    those elements Xi of List1 for which call(Goal, Xi) succeeds.

Usage example:

?- include(number, [a(b), 2, _, 1.2, C, '1'], L).
L = [2, 1.2].

Now your homework becomes "how to implement include/3". Once you have implemented your version of include/3 you can check if it matches SWI's version by looking at its source code: listing(include).