add union

prelude/__internal__/List.mad

@@ -1084,14 +1084,36 @@ export cut = (a, xs) => {
     Nothing
   }
 }
-
+/**
+ * Finds the set (i.e. no duplicates) of all elements in the first list not contained in the second list. 
+ * @example
+ * difference([1,2,3,4], [7,6,5,4,3]) // [1,2]
+ * difference([7,6,5,4,3], [1,2,3,4]) // [7,6,5]
+ */
 difference :: Eq a => List a -> List a -> List a
 export difference = (z, a) => reduce((stack, c) => includes(c, a) ? stack : [...stack, c], [], z)
 
-
+/**
+ * Finds the set (i.e. no duplicates) of all elements contained in the first or second list, but not both.
+ * @example
+ * symmetricDifference([1,2,3,4], [7,6,5,4,3]) // [1,2,7,6,5]
+ * symmetricDifference([7,6,5,4,3], [1,2,3,4]) // [7,6,5,1,2]
+ */
 symmetricDifference :: Eq a => List a -> List a -> List a
 export symmetricDifference = (z, a) => reduce(
   (stack, c) => includes(c, a) && includes(c, z) ? stack : [...stack, c],
   [],
   concat(z, a),
 )
+
+/**
+ * Combines two lists into a set (i.e. no duplicates) composed of the elements of each list
+ * @example
+ * union([1, 2, 3], [2, 3, 4]) // [1, 2, 3, 4]
+ */
+union :: Eq a => List a -> List a -> List a
+export union = (a, z) => reduce(
+  (stack, c) => includes(c, stack) ? stack : [...stack, c],
+  [],
+  concat(a, z),
+)

prelude/__internal__/List.spec.mad

@@ -45,6 +45,7 @@ import {
   take,
   takeLast,
   takeWhile,
+  union,
   uniqueBy,
 } from "./List"
 
@@ -302,3 +303,5 @@ test(
   "symmetricDifference",
   () => assertEquals(symmetricDifference([7, 6, 5, 4, 3], [1, 2, 3, 4]), [7, 6, 5, 1, 2]),
 )
+
+test("union", () => assertEquals(union(range(1, 11), range(11, 21)), range(1, 21)))