Initial data commit

Task/Sierpinski-triangle/JavaScript/sierpinski-triangle-5.js

@@ -0,0 +1,69 @@
+(() => {
+    "use strict";
+
+    // --------------- SIERPINSKI TRIANGLE ---------------
+
+    // sierpinski :: Int -> [Bool]
+    const sierpinski = intOrder =>
+        // Reduce/folding from the last item (base of list)
+        // which has zero left indent.
+
+        // Each preceding row has one more indent space
+        // than the row beneath it.
+        pascalMod2Chars(2 ** intOrder)
+        .reduceRight((a, x) => ([
+            `${a[1]}${x.join(" ")}\n${a[0]}`,
+            `${a[1]} `
+        ]), ["", ""])[0];
+
+
+    // pascalMod2Chars :: Int -> [[Char]]
+    const pascalMod2Chars = nRows =>
+        enumFromTo(1)(nRows - 1)
+        .reduce(sofar => {
+            const rows = sofar.slice(-1)[0];
+
+            // Rule 90 also reduces to the same XOR
+            // relationship between left and right neighbours.
+            return ([
+                ...sofar,
+                zipWith(
+                    l => r => l === r ? (
+                        " "
+                    ) : "*"
+                )([" ", ...rows])([...rows, " "])
+            ]);
+        }, [
+            ["*"]
+        ]);
+
+    // ---------------------- TEST -----------------------
+    // main :: IO ()
+    const main = () =>
+        sierpinski(4);
+
+
+    // --------------------- GENERIC ---------------------
+
+    // zipWith :: (a -> b -> c) -> [a] -> [b] -> [c]
+    const zipWith = f =>
+        // A list constructed by zipping with a
+        // custom function, rather than with the
+        // default tuple constructor.
+        xs => ys => xs.map(
+            (x, i) => f(x)(ys[i])
+        ).slice(
+            0, Math.min(xs.length, ys.length)
+        );
+
+
+    // enumFromTo :: Int -> Int -> [Int]
+    const enumFromTo = m =>
+        n => Array.from({
+            length: 1 + n - m
+        }, (_, i) => m + i);
+
+
+    // MAIN ---
+    return main();
+})();