Initial data commit

Task/Sierpinski-triangle/JavaScript/sierpinski-triangle-4.js

@@ -0,0 +1,70 @@
+(() => {
+    "use strict";
+
+    // ----- LINES OF SIERPINSKI TRIANGLE AT LEVEL N -----
+
+    // sierpinski :: Int -> [String]
+    const sierpTriangle = n =>
+        // Previous triangle centered with
+        // left and right padding,
+        0 < n ? (
+            ap([
+                map(
+                    xs => ap([
+                        compose(
+                            ks => ks.join(""),
+                            replicate(2 ** (n - 1))
+                        )
+                    ])([" ", "-"])
+                    .join(xs)
+                ),
+
+                // above a pair of duplicates,
+                // placed one character apart.
+                map(s => `${s}+${s}`)
+            ])([sierpTriangle(n - 1)])
+            .flat()
+        ) : ["▲"];
+
+
+    // ---------------------- TEST -----------------------
+    const main = () =>
+        sierpTriangle(4)
+        .join("\n");
+
+
+    // ---------------- GENERIC FUNCTIONS ----------------
+
+    // ap (<*>) :: [(a -> b)] -> [a] -> [b]
+    const ap = fs =>
+        // The sequential application of each of a list
+        // of functions to each of a list of values.
+        // apList([x => 2 * x, x => 20 + x])([1, 2, 3])
+        //     -> [2, 4, 6, 21, 22, 23]
+        xs => fs.flatMap(f => xs.map(f));
+
+
+    // compose (<<<) :: (b -> c) -> (a -> b) -> a -> c
+    const compose = (...fs) =>
+        // A function defined by the right-to-left
+        // composition of all the functions in fs.
+        fs.reduce(
+            (f, g) => x => f(g(x)),
+            x => x
+        );
+
+
+    // map :: (a -> b) -> [a] -> [b]
+    const map = f => xs => xs.map(f);
+
+
+    // replicate :: Int -> a -> [a]
+    const replicate = n =>
+        // A list of n copies of x.
+        x => Array.from({
+            length: n
+        }, () => x);
+
+    // ---------------------- TEST -----------------------
+    return main();
+})();