ES6 Compose

compose.js

const compose = (...args) => initial => args.reduceRight(
    (result, fn) => fn(result),
    initial
);

Type signature is something like compose :: (c, b, a, ...) -> (x, y, z, ...) -> ...(c(b(a(x, y, z, ...))))

@neftaly

const compose = ([ firstArg, ...restArgs ]) => (...initial) => restArgs.reduceRight(
    (result, fn) => fn(result),
    firstArg(...initial)
);

this implementation is broken in sense that for compose right most function can be any arity, and in this example its left most

---

// Same thing, written differently
const compose = (...args) => (...initial) => args.reduceRight(
    (result, fn) => [ fn(...result) ],
    initial
)[0];

this implementation will be broken if any function inside compose will return array as a value, so next function will take this array not as first argument, but as arguments as a whole

@neftaly @meChrisReed

Working as intended implementation should look like this:

const compose = (...fns) => {
  const [tailFn, ...restFns] = fns.reverse();
  return (...args) => restFns.reduce(
    (value, fn) => fn(value),
    tailFn(...args)
  );
};

const pipe = (...fns) => compose(...fns.reverse());

Or other way around

const pipe = (headFn, ...restFns) => (...args) => restFns.reduce(
  (value, fn) => fn(value),
  headFn(...args)
);

const compose = (...fns) => pipe(...fns.reverse());

@iamstarkov How does the functions handle functions with two arguments? Could you give me an example or how to modify the code so it handles them?

Hello, here's my version https://gist.github.com/WaldoJeffers/905e14d03f4283599bac753f73b7716b. Does it cover your use cases ?