2016 Update

Task/Pascals-triangle/JavaScript/pascals-triangle-4.js

@@ -0,0 +1,50 @@
+(() => {
+    'use strict';
+
+    // pascal :: Int -> [[Int]]
+    let pascal = n =>
+            range(1, n - 1)
+            .reduce(a => {
+                let lstPreviousRow = a.slice(-1)[0];
+
+                return a
+                    .concat([zipWith((a, b) => a + b,
+                        [0].concat(lstPreviousRow),
+                        lstPreviousRow.concat(0)
+                    )]);
+            }, [
+                [1]
+            ]);
+
+    // GENERIC FUNCTIONS
+
+    // Int -> Int -> Maybe Int -> [Int]
+    let range = (m, n, step) => {
+                let d = (step || 1) * (n >= m ? 1 : -1);
+                return Array.from({
+                    length: Math.floor((n - m) / d) + 1
+                }, (_, i) => m + (i * d));
+            },
+
+        // zipWith :: (a -> b -> c) -> [a] -> [b] -> [c]
+        zipWith = (f, xs, ys) =>
+            xs.length === ys.length ? (
+                xs.map((x, i) => f(x, ys[i]))
+            ) : undefined;
+
+    // TEST
+    return pascal(7)
+        .reduceRight((a, x) => {
+            let strIndent = a.indent;
+
+            return {
+                rows: strIndent + x
+                    .map(n => ('    ' + n).slice(-4))
+                    .join('') + '\n' + a.rows,
+                indent: strIndent + '  '
+            };
+        }, {
+            rows: '',
+            indent: ''
+        }).rows;
+})();