Sample Execution of Transducers

transducers.ts

const ELEMENTS = 1000000;

const add10 = (a: number) => a + 10;
const isEven = (a: number) => a % 2 === 0;

const getInitial = (): number[] => [];
const combine = (acc: number[], elem: number) => (acc.push(elem), acc);
const compose = (...fns: Function[]) => (x: number) => fns.reduceRight<number>((acc, fn) => fn(acc), x);

const ip = Array.from(Array(ELEMENTS), (_, i) => i);

const add20AndFilterEven = compose(
  add10,
  add10,
  isEven
);

console.time('simple');
ip.map(add10)
  .map(add10)
  .filter(isEven);
console.timeEnd('simple');

console.time('composed');
ip.map(add20AndFilterEven);
console.timeEnd('composed');


const map = (mapFn: (a: number) => number) => (combine: (acc: number[], elem: number) => number[]) => (acc: number[], elem: number) => combine(acc, mapFn(elem));
const filter = (predicateFn: (a: number) => boolean) => (combine: (acc: number[], elem: number) => number[]) => (acc: number[], elem: number) => (predicateFn(elem) ? combine(acc, elem) : acc);

const xduce = (xform: Function, combine: (acc: number[], elem: number) => number[], getInitial: () => number[]) => (inputArr: number[]) => inputArr.reduce(xform(combine), getInitial());

const xform = compose(
  map(add10),
  map(add10),
  filter(isEven)
);

const transform = xduce(xform, combine, getInitial);
console.time('mapWithRf');
transform(ip);
console.timeEnd('mapWithRf');

For 1M entries time take is as follows:

simple: 221.453ms
composed: 138.141ms
mapWithRf: 41.848ms