Initial data commit

Task/Permutations/JavaScript/permutations-8.js

@@ -0,0 +1,42 @@
+(() => {
+    'use strict';
+
+    // permutations :: [a] -> [[a]]
+    const permutations = xs =>
+        xs.reduceRight(
+            (a, x) => concatMap(
+                xs => enumFromTo(0, xs.length)
+                .map(n => xs.slice(0, n)
+                    .concat(x)
+                    .concat(xs.slice(n))
+                ),
+                a
+            ),
+            [[]]
+        );
+
+    // GENERIC FUNCTIONS ----------------------------------
+
+    // concatMap :: (a -> [b]) -> [a] -> [b]
+    const concatMap = (f, xs) =>
+        xs.reduce((a, x) => a.concat(f(x)), []);
+
+    // ft :: Int -> Int -> [Int]
+    const enumFromTo = (m, n) =>
+        Array.from({
+            length: 1 + n - m
+        }, (_, i) => m + i);
+
+    // showLog :: a -> IO ()
+    const showLog = (...args) =>
+        console.log(
+            args
+            .map(JSON.stringify)
+            .join(' -> ')
+        );
+
+    // TEST -----------------------------------------------
+    showLog(
+        permutations([1, 2, 3])
+    );
+})();