Improve adjust exact and range implementation

Author: przemyslawzalewski

array/exact.js

@@ -1,4 +1,3 @@
-export default n => source =>
-  Array(n)
-    .fill()
-    .map((_, i) => source[i]);
+import range from "./range.js";
+
+export default n => xs => range(n).map(index => xs[index]);

array/range.js

@@ -1,4 +1,4 @@
 export default n =>
   Array(n)
     .fill()
-    .map((_, i) => i);
+    .map((_, index) => index);