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Functional Programming Patterns With RamdaJS!

Compose

Understand how compose works in RamdaJS to combine functions from right to left. Learn to reverse operation order compared to pipe and grasp how this approach aligns with mathematical function composition.

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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.

Javascript (babel-node)
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.

Javascript (babel-node)
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.

Javascript (babel-node)
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.

Javascript (babel-node)
increment(triple(square(double(x))));