September 2017 Update

Task/Phrase-reversals/JavaScript/phrase-reversals-2.js

@@ -0,0 +1,65 @@
+(() => {
+    'use strict'
+
+    // reverseString, reverseEachWord, reverseWordOrder :: String -> String
+    const
+        reverseString = s => reverse(s),
+
+        reverseEachWord = s => wordLevel(map(reverse))(s),
+
+        reverseWordOrder = s => wordLevel(reverse)(s);
+
+    // wordLevel :: ([String] -> [String]) -> String -> String
+    const wordLevel = f =>
+        x => unwords(f(words(x)));
+
+
+    // GENERIC FUNCTIONS -----------------------------------------------------
+
+    // A list of functions applied to a list of arguments
+    // <*> :: [(a -> b)] -> [a] -> [b]
+    const ap = (fs, xs) => //
+        [].concat.apply([], fs.map(f => //
+            [].concat.apply([], xs.map(x => [f(x)]))));
+
+    // 2 or more arguments
+    // curry :: Function -> Function
+    const curry = (f, ...args) => {
+        const go = xs => xs.length >= f.length ? (f.apply(null, xs)) :
+            function () {
+                return go(xs.concat(Array.from(arguments)));
+            };
+        return go([].slice.call(args, 1));
+    };
+
+    // map :: (a -> b) -> [a] -> [b]
+    const map = curry((f, xs) => xs.map(f));
+
+    // reverse :: [a] -> [a]
+    const reverse = curry(xs =>
+        typeof xs === 'string' ? (
+            xs.split('')
+            .reverse()
+            .join('')
+        ) : xs.slice(0)
+        .reverse());
+
+    // unlines :: [String] -> String
+    const unlines = xs => xs.join('\n');
+
+    // unwords :: [String] -> String
+    const unwords = xs => xs.join(' ');
+
+    // words :: String -> [String]
+    const words = s => s.split(/\s+/);
+
+
+    // TEST ------------------------------------------------------------------
+    return unlines(
+        ap([
+            reverseString,
+            reverseEachWord,
+            reverseWordOrder
+        ], ["rosetta code phrase reversal"])
+    );
+})();