2016 Update

Task/Zeckendorf-number-representation/JavaScript/zeckendorf-number-representation.js

@@ -0,0 +1,61 @@
+(() => {
+    'use strict';
+
+    // zeckendorf :: Int -> String
+    function zeckendorf(n) {
+        let f = (n, x) => (n < x ? [n, 0] : [n - x, 1]);
+
+        return (n === 0 ? (
+                [0]
+            ) : mapAccumL(f, n, reverse(tail(fibUntil(n))))[1])
+            .join('');
+    }
+
+
+    // fibUntil :: Int -> [Int]
+    let fibUntil = n => {
+        let xs = [];
+        until(
+            ([a, b]) => a > n,
+            ([a, b]) => (xs.push(a), [b, a + b]), [1, 1]
+        )
+        return xs;
+    }
+
+    // GENERIC FUNCTIONS
+
+    // mapAccumL :: (acc -> x -> (acc, y)) -> acc -> [x] -> (acc, [y])
+    let mapAccumL = (f, acc, xs) => {
+        return xs.reduce((a, x) => {
+            let pair = f(a[0], x);
+
+            return [pair[0], a[1].concat(pair[1])];
+        }, [acc, []]);
+    }
+
+    // until :: (a -> Bool) -> (a -> a) -> a -> a
+    let until = (p, f, x) => {
+        let v = x;
+        while (!p(v)) v = f(v);
+        return v;
+    }
+
+    // tail :: [a] -> [a]
+    let tail = xs => xs.length ? xs.slice(1) : undefined;
+
+    // reverse :: [a] -> [a]
+    let reverse = xs => xs.slice(0)
+        .reverse();
+
+    // range :: Int -> Int -> [Int]
+    let range = (m, n) =>
+        Array.from({
+            length: Math.floor(n - m) + 1
+        }, (_, i) => m + i);
+
+    // TEST
+    return range(0, 20)
+        .map(zeckendorf)
+        .join('\n')
+
+})();