added map to sets

lib/pure/collections/sets.nim

@@ -241,3 +241,7 @@ proc `<=`*[A](s, t: TSet[A]): bool =
       
 proc `==`*[A](s, t: TSet[A]): bool =
   s.counter == t.counter and s <= t
+
+proc map*[A, B](data: TSet[A], op: proc (x: A): B {.closure.}): TSet[A] =
+  result = initSet[B]()
+  for i in data: result.incl(op(i))

tests/stdlib/tsets.nim

@@ -0,0 +1,13 @@
+discard """
+  output: '''true'''
+"""
+
+import sets
+var
+  a = initSet[int]()
+  b = initSet[int]()
+
+for i in 0..5: a.incl(i)
+for i in 1..6: b.incl(i)
+
+echo map(a, proc(x: int): int = x + 1) == b