tasks a-s

Task/Permutations/Logtalk/permutations-1.logtalk

@@ -0,0 +1,22 @@
+:- object(list).
+
+    :- public(permutation/2).
+
+    permutation(List, Permutation) :-
+        same_length(List, Permutation),
+        permutation2(List, Permutation).
+
+    permutation2([], []).
+    permutation2(List, [Head| Tail]) :-
+        select(Head, List, Remaining),
+        permutation2(Remaining, Tail).
+
+    same_length([], []).
+    same_length([_| Tail1], [_| Tail2]) :-
+        same_length(Tail1, Tail2).
+
+    select(Head, [Head| Tail], Tail).
+    select(Head, [Head2| Tail], [Head2| Tail2]) :-
+        select(Head, Tail, Tail2).
+
+:- end_object.

Task/Permutations/Logtalk/permutations-2.logtalk

@@ -0,0 +1,9 @@
+| ?- forall(list::permutation([1, 2, 3], Permutation), (write(Permutation), nl)).
+
+[1,2,3]
+[1,3,2]
+[2,1,3]
+[2,3,1]
+[3,1,2]
+[3,2,1]
+yes