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