prolog-recursion-more.pro

/**
 * Let's define a member function to tell if x is a member of ary
 *
 * def member(x, ary)
 *   return false if ary == []
 *   return true if ary.first == x
 *   member(x, ary[1...ary.size])
 * end
 *
 * In Prolog:
 */
is_member(H, [H | _]).
is_member(X, [_ | T]) :- member(X, T).

% using member to get "different functions"
iterate :- is_member(Member, [1, 2, 3]), print(Member), nl.
generate :- is_member(1, List), print(List), nl.


/**
 * Now, let's define a length function
 * def length(ary)
 *   return 0 if ary.eql? []
 *   length(ary.rest) + 1
 * end
 *
 * In Prolog:
 */
size(0, []).
size(N, [_ | T]) :- size(N1, T), N is N1 + 1.

lists_of_size_2 :- size(2, List), print(List), nl.