2016 Update

Task/Range-expansion/JavaScript/range-expansion-4.js

@@ -0,0 +1,37 @@
+(strTest => {
+
+    // expansion :: String -> [Int]
+    let expansion = strExpr =>
+
+        // concat map yields flattened output list
+        [].concat.apply([], strExpr.split(',')
+            .map(x => x.split('-')
+                .reduce((a, s, i, l) =>
+
+                    // negative (after item 0) if preceded by an empty string
+                    // (i.e. a hyphen-split artefact, otherwise ignored)
+                    s.length ? i ? a.concat(
+                        parseInt(l[i - 1].length ? s :
+                            '-' + s, 10)
+                    ) : [+s] : a, [])
+
+                // two-number lists are interpreted as ranges
+            )
+            .map(r => r.length > 1 ? range.apply(null, r) : r)),
+
+
+
+        // range :: Int -> Int -> Maybe Int -> [Int]
+        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));
+        };
+
+
+
+    return expansion(strTest);
+
+})('-6,-3--1,3-5,7-11,14,15,17-20');