Initial data commit

Task/Egyptian-division/JavaScript/egyptian-division.js

@@ -0,0 +1,89 @@
+(() => {
+    'use strict';
+
+    // EGYPTIAN DIVISION --------------------------------
+
+    // eqyptianQuotRem :: Int -> Int -> (Int, Int)
+    const eqyptianQuotRem = (m, n) => {
+        const expansion = ([i, x]) =>
+            x > m ? (
+                Nothing()
+            ) : Just([
+                [i, x],
+                [i + i, x + x]
+            ]);
+        const collapse = ([i, x], [q, r]) =>
+            x < r ? (
+                [q + i, r - x]
+            ) : [q, r];
+        return foldr(
+            collapse,
+            [0, m],
+            unfoldr(expansion, [1, n])
+        );
+    };
+
+    // TEST ---------------------------------------------
+
+    // main :: IO ()
+    const main = () =>
+        showLog(
+            eqyptianQuotRem(580, 34)
+        );
+        // -> [17, 2]
+
+
+
+    // GENERIC FUNCTIONS --------------------------------
+
+    // Just :: a -> Maybe a
+    const Just = x => ({
+        type: 'Maybe',
+        Nothing: false,
+        Just: x
+    });
+
+    // Nothing :: Maybe a
+    const Nothing = () => ({
+        type: 'Maybe',
+        Nothing: true,
+    });
+
+    // flip :: (a -> b -> c) -> b -> a -> c
+    const flip = f =>
+        1 < f.length ? (
+            (a, b) => f(b, a)
+        ) : (x => y => f(y)(x));
+
+
+    // foldr :: (a -> b -> b) -> b -> [a] -> b
+    const foldr = (f, a, xs) => xs.reduceRight(flip(f), a);
+
+
+    // unfoldr :: (b -> Maybe (a, b)) -> b -> [a]
+    const unfoldr = (f, v) => {
+        let
+            xr = [v, v],
+            xs = [];
+        while (true) {
+            const mb = f(xr[1]);
+            if (mb.Nothing) {
+                return xs
+            } else {
+                xr = mb.Just;
+                xs.push(xr[0])
+            }
+        }
+    };
+
+    // showLog :: a -> IO ()
+    const showLog = (...args) =>
+        console.log(
+            args
+            .map(JSON.stringify)
+            .join(' -> ')
+        );
+
+    // MAIN ---
+    return main();
+})();