Initial data commit

Task/Department-numbers/JavaScript/department-numbers-2.js

@@ -0,0 +1,79 @@
+(function () {
+    'use strict';
+
+    // NUMBERING CONSTRAINTS --------------------------------------------------
+
+    // options :: Int -> Int -> Int -> [(Int, Int, Int)]
+    function options(lo, hi, total) {
+        var bind = flip(concatMap),
+            ds = enumFromTo(lo, hi);
+
+        return bind(filter(even, ds),
+            function (x) { // X is even,
+                return bind(filter(function (d) { return d !== x; }, ds),
+            function (y) { // Y is distinct from X,
+                return bind([total - (x + y)],
+            function (z) { // Z sums with x and y to total, and is in ds.
+                return z !== y && lo <= z && z <= hi ? [
+                    [x, y, z]
+                ] : [];
+            })})})};
+
+    // GENERIC FUNCTIONS ------------------------------------------------------
+
+    // concatMap :: (a -> [b]) -> [a] -> [b]
+    function concatMap(f, xs) {
+        return [].concat.apply([], xs.map(f));
+    };
+
+    // enumFromTo :: Int -> Int -> [Int]
+    function enumFromTo(m, n) {
+        return Array.from({
+            length: Math.floor(n - m) + 1
+        }, function (_, i) {
+            return m + i;
+        });
+    };
+
+    // even :: Integral a => a -> Bool
+    function even(n) {
+        return n % 2 === 0;
+    };
+
+    // filter :: (a -> Bool) -> [a] -> [a]
+    function filter(f, xs) {
+        return xs.filter(f);
+    };
+
+    // flip :: (a -> b -> c) -> b -> a -> c
+    function flip(f) {
+        return function (a, b) {
+            return f.apply(null, [b, a]);
+        };
+    };
+
+    // length :: [a] -> Int
+    function length(xs) {
+        return xs.length;
+    };
+
+    // map :: (a -> b) -> [a] -> [b]
+    function map(f, xs) {
+        return xs.map(f);
+    };
+
+    // show :: a -> String
+    function show(x) {
+        return JSON.stringify(x);
+    }; //, null, 2);
+
+    // unlines :: [String] -> String
+    function unlines(xs) {
+        return xs.join('\n');
+    };
+
+    // TEST -------------------------------------------------------------------
+    var xs = options(1, 7, 12);
+    return '(Police, Sanitation, Fire)\n\n' +
+        unlines(map(show, xs)) + '\n\nNumber of options: ' + length(xs);
+})();