CODEWITHSUNDEEP
listprologlist-manipulation
user3916311
user3916311

Reputation: 1

SWI Prolog mult every element of list

I want to write a predicate that will be taking every element from my list and mult with others without duplicates.

Examples:

?- predicate([2,3,5,6],X).
X = [6,10,12,15,18,30].        % expected result

?- predicate([1,6,10],X).
X = [6,10,60].                 % expected result

I was trying something like this, but I don't know how to upgrade this code:

predicate([],[]).
predicate([_|[]],[]) :-
    !.
predicate([H,S|T],[V|X]) :-
    V is H*S,
    predicate([H|T],X).

Upvotes: 0

Views: 311

Answers (1)

Wouter Beek
Wouter Beek

Reputation: 3407

The following gives the results you describe:

predicate(Xs, Ys):-
  aggregate_all(
    set(Y),
    (
      member(X1, Xs),
      member(X2, Xs),
      X1 =\= X2,
      Y is X1 * X2
    ),
    Ys
  ).

Notice that aggregate_all/3 is a non-standard predicate from library aggregate. There are alternative implementations that use the ISO predicate bagof/3.

Upvotes: 1

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