September Morn Update

Task/Greatest-subsequential-sum/JavaScript/greatest-subsequential-sum-2.js

@@ -0,0 +1,59 @@
+(() => {
+
+    // maxSubseq :: [Int] -> (Int, [Int])
+    const maxSubseq = xs =>
+        snd(xs.reduce((tpl, x) => {
+            const [m1, m2] = Array.from(fst(tpl)),
+                high = max(
+                    Tuple(0, []),
+                    Tuple(m1 + x, m2.concat(x))
+                );
+            return Tuple(high, max(snd(tpl), high));
+        }, Tuple(Tuple(0, []), Tuple(0, []))));
+
+
+    // TEST -----------------------------------------------
+    // main :: IO ()
+    const main = () => {
+        const mx = maxSubseq([-1, -2, 3, 5, 6, -2, -1, 4, -4, 2, -1]);
+        showLog(snd(mx), fst(mx))
+    }
+    // [3,5,6,-2,-1,4] -> 15
+
+
+    // GENERIC FUNCTIONS ----------------------------------
+
+    // fst :: (a, b) -> a
+    const fst = tpl => tpl[0];
+
+    // gt :: Ord a => a -> a -> Bool
+    const gt = (x, y) =>
+        'Tuple' === x.type ? (
+            x[0] > y[0]
+        ) : (x > y);
+
+    // max :: Ord a => a -> a -> a
+    const max = (a, b) => gt(b, a) ? b : a;
+
+    // showLog :: a -> IO ()
+    const showLog = (...args) =>
+        console.log(
+            args
+            .map(JSON.stringify)
+            .join(' -> ')
+        );
+
+    // snd :: (a, b) -> b
+    const snd = tpl => tpl[1];
+
+    // Tuple (,) :: a -> b -> (a, b)
+    const Tuple = (a, b) => ({
+        type: 'Tuple',
+        '0': a,
+        '1': b,
+        length: 2
+    });
+
+    // MAIN ---
+    return main();
+})();