Compose

Pipe, but in the other direction. (2 min. read)

If pipe made sense, you already know compose. Instead of going left-to-right, we go right-to-left.

This returns 49 since we’re using pipe.

import { pipe } from 'ramda';
const doMath = pipe(
  // start here
  double, // 2 * 2 = 4
  square, // 16
  triple, // 48
  increment // 49
);
const result = doMath(2);
console.log({ result });

But the same sequence with compose returns 162, since the order of operations have reversed.

import { compose } from 'ramda';
const doMath = compose(
  double, // 162
  square, // 81
  triple, // 9
  increment // 2 + 1 = 3
  // start here
);
const result = doMath(2);
console.log({ result });

To get 49, like pipe, flip the sequence.

import { compose } from 'ramda';
const doMath = compose(
  increment, // 49
  triple, // 48
  square, // 16
  double // 2 * 2 = 4
  // start here
);
const result = doMath(2);
console.log({ result });

compose mirrors the mathematical form of composition–the innermost function goes first.

increment(triple(square(double(x))));