fix append so it does not mutate

Author: Kingsley Hendrickse

js/array_extra.js

@@ -1,10 +1,3 @@
-function concat(a, b) {
-    return a.reduceRight(function (coll, item) {
-        coll.unshift(item);
-        return coll;
-    }, b);
-}
-
 function groupsOf(arr, size) {
     var arrMulti = [];
     var groups = Math.ceil(arr.length/size);

source/ArrayExtra.mint

@@ -15,7 +15,7 @@ module Array.Extra {
     Array.Extra.append([1,1,2] [3,5,8]) == [1,1,2,3,5,8]
   */
   fun append (array1 : Array(a), array2 : Array(a)) : Array(a) {
-    `concat(array1, array2)`
+    `array1.concat(array2)`
   }
 
   /*

tests/ArrayExtra.mint

@@ -192,3 +192,43 @@ suite "Array groupsOf" {
     }
   }
 }
+
+suite "Array functions should not mutate existing arrays" {
+  test "append should not mutate" {
+    try {
+      a =
+        [
+          1,
+          2,
+          3
+        ]
+
+      b =
+        [
+          4,
+          5,
+          6
+        ]
+
+      c =
+        Array.Extra.append(a, b)
+
+      (a == [
+        1,
+        2,
+        3
+      ] && b == [
+        4,
+        5,
+        6
+      ] && c == [
+        1,
+        2,
+        3,
+        4,
+        5,
+        6
+      ])
+    }
+  }
+}