Initial data commit

Task/Permutations/JavaScript/permutations-6.js

@@ -0,0 +1,39 @@
+(() => {
+    'use strict';
+
+    // permutations :: [a] -> [[a]]
+    const permutations = xs => {
+        const go = xs => xs.length ? (
+            concatMap(
+                x => concatMap(
+                    ys => [[x].concat(ys)],
+                    go(delete_(x, xs))), xs
+                )
+        ) : [[]];
+        return go(xs);
+    };
+
+    // GENERIC FUNCTIONS ----------------------------------
+
+    // concatMap :: (a -> [b]) -> [a] -> [b]
+    const concatMap = (f, xs) =>
+        xs.reduce((a, x) => a.concat(f(x)), []);
+
+
+    // delete :: Eq a => a -> [a] -> [a]
+    const delete_ = (x, xs) => {
+        const go = xs => {
+            return 0 < xs.length ? (
+                (x === xs[0]) ? (
+                    xs.slice(1)
+                ) : [xs[0]].concat(go(xs.slice(1)))
+            ) : [];
+        }
+        return go(xs);
+    };
+
+    // TEST
+    return JSON.stringify(
+        permutations(['Aardvarks', 'eat', 'ants'])
+    );
+})();