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Garciat/functional.js

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 /* Lazy */ class Memoized { constructor(it) { this.it = it; this.done = false; this.mem = []; } [Symbol.iterator]() { return new MemoizedIterator(this); } } class MemoizedIterator { constructor(m) { this.m = m; this.i = 0; } next() { if (this.i < this.m.mem.length) { return { value: this.m.mem[this.i++], done: false }; } if (this.m.done) { return { value: undefined, done: true }; } const res = this.m.it.next(); if (res.done) { this.m.done = true; return { value: undefined, done: true }; } const val = res.value; this.m.mem[this.i] = val; this.i += 1; return { value: val, done: false }; } } function memoized(f) { return new Chain(new Memoized(f())); } /* Iterator */ function* map(xs, f) { for (let x of xs) { yield f(x); } } function* flatMap(xs, f) { for (let x of xs) { yield* f(x); } } function forEach(xs, f) { for (let x of xs) { f(x); } } function* take(xs, n) { let i = 0; for (let x of xs) { if (i >= n) { break; } yield x; i += 1; } } function* cycle(xs) { while (true) { yield* xs; } } function* pairwise(xs) { const sentinel = {}; let last = sentinel; for (let x of xs) { if (last !== sentinel) { yield [last, x]; } last = x; } } function* takeWhile(xs, f) { for (let x of xs) { if (!f(x)) { break; } yield x; } } function* concat(xs, ys) { yield* xs; yield* ys; } function* zipWith(xs, ys, f) { const itx = xs[Symbol.iterator](); const ity = ys[Symbol.iterator](); while (true) { const rx = itx.next(); const ry = ity.next(); if (rx.done || ry.done) { return; } const x = rx.value; const y = ry.value; yield f(x, y); } } function* tail(xs) { const itx = xs[Symbol.iterator](); let rx = itx.next(); if (rx.done) { return; } while (true) { const rx = itx.next(); if (rx.done) { return; } yield rx.value; } } function zip(xs, ys) { return zipWith(xs, ys, (x, y) => [x, y]); } function reduce(xs, o, f) { let s = o; for (let x of xs) { s = f(s, x); } return s; } function* filter(xs, f) { for (let x of xs) { if (f(x)) { yield x; } } } /* Chaining */ class Chain { constructor(xs) { this.xs = xs; } [Symbol.iterator]() { return this.xs[Symbol.iterator](); } forEach(f) { return forEach(this.xs, f); } reduce(o, f) { return reduce(this.xs, o, f); } toArray() { return Array.from(this.xs); } } const CHAIN_OPERATORS = [ map, flatMap, take, cycle, pairwise, takeWhile, concat, zipWith, tail, zip, filter ]; for (let op of CHAIN_OPERATORS) { Chain.prototype[op.name] = function (...args) { args.unshift(this); return new Chain(op.apply(undefined, args)); }; } function chain(xs) { return new Chain(xs); }
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