Data commit

Task/Find-the-intersection-of-two-lines/JavaScript/find-the-intersection-of-two-lines.js

@@ -0,0 +1,74 @@
+(() => {
+    'use strict';
+    // INTERSECTION OF TWO LINES ----------------------------------------------
+
+    // intersection :: Line -> Line -> Either String (Float, Float)
+    const intersection = (ab, pq) => {
+        const
+            delta = f => x => f(fst(x)) - f(snd(x)),
+            [abDX, pqDX, abDY, pqDY] = apList(
+                [delta(fst), delta(snd)], [ab, pq]
+            ),
+            determinant = abDX * pqDY - abDY * pqDX;
+
+        return determinant !== 0 ? Right((() => {
+            const [abD, pqD] = map(
+                ([a, b]) => fst(a) * snd(b) - fst(b) * snd(a),
+                [ab, pq]
+            );
+            return apList(
+                [([pq, ab]) =>
+                    (abD * pq - ab * pqD) / determinant
+                ], [
+                    [pqDX, abDX],
+                    [pqDY, abDY]
+                ]
+            );
+        })()) : Left('(Parallel lines – no intersection)');
+    };
+
+    // GENERIC FUNCTIONS ------------------------------------------------------
+
+    // Left :: a -> Either a b
+    const Left = x => ({
+        type: 'Either',
+        Left: x
+    });
+
+    // Right :: b -> Either a b
+    const Right = x => ({
+        type: 'Either',
+        Right: x
+    });
+
+    // A list of functions applied to a list of arguments
+    // <*> :: [(a -> b)] -> [a] -> [b]
+    const apList = (fs, xs) => //
+        [].concat.apply([], fs.map(f => //
+            [].concat.apply([], xs.map(x => [f(x)]))));
+
+    // fst :: (a, b) -> a
+    const fst = tpl => tpl[0];
+
+    // map :: (a -> b) -> [a] -> [b]
+    const map = (f, xs) => xs.map(f);
+
+    // snd :: (a, b) -> b
+    const snd = tpl => tpl[1];
+
+    // show :: a -> String
+    const show = x => JSON.stringify(x); //, null, 2);
+
+
+    // TEST --------------------------------------------------
+
+    // lrIntersection ::Either String Point
+    const lrIntersection = intersection([
+        [4.0, 0.0],
+        [6.0, 10.0]
+    ], [
+        [0.0, 3.0],
+        [10.0, 7.0]
+    ]);
+    return show(lrIntersection.Left || lrIntersection.Right);
+})();