Initial data commit

Task/Catalan-numbers/JavaScript/catalan-numbers-2.js

@@ -0,0 +1,85 @@
+(() => {
+    "use strict";
+
+    // ----------------- CATALAN NUMBERS -----------------
+
+    // catalansDefinitionThree :: [Int]
+    const catalansDefinitionThree = () =>
+        // An infinite sequence of Catalan numbers.
+        scanlGen(
+            c => n => Math.floor(
+                (2 * c * pred(2 * n)) / succ(n)
+            )
+        )(1)(
+            enumFrom(1)
+        );
+
+
+    // ---------------------- TEST -----------------------
+    // main :: IO ()
+    const main = () =>
+        take(15)(
+            catalansDefinitionThree()
+        );
+
+
+    // --------------------- GENERIC ---------------------
+
+    // enumFrom :: Enum a => a -> [a]
+    const enumFrom = function* (n) {
+        // An infinite sequence of integers,
+        // starting with n.
+        let v = n;
+
+        while (true) {
+            yield v;
+            v = 1 + v;
+        }
+    };
+
+
+    // pred :: Int -> Int
+    const pred = x =>
+        x - 1;
+
+
+    // scanlGen :: (b -> a -> b) -> b -> Gen [a] -> [b]
+    const scanlGen = f =>
+        // The series of interim values arising
+        // from a catamorphism over an infinite list.
+        startValue => function* (gen) {
+            let
+                a = startValue,
+                x = gen.next();
+
+            yield a;
+            while (!x.done) {
+                a = f(a)(x.value);
+                yield a;
+                x = gen.next();
+            }
+        };
+
+
+    // succ :: Int -> Int
+    const succ = x =>
+        1 + x;
+
+
+    // take :: Int -> [a] -> [a]
+    // take :: Int -> String -> String
+    const take = n =>
+        // The first n elements of a list,
+        // string of characters, or stream.
+        xs => Array.from({
+            length: n
+        }, () => {
+            const x = xs.next();
+
+            return x.done ? [] : [x.value];
+        }).flat();
+
+
+    // MAIN ---
+    return JSON.stringify(main(), null, 2);
+})();