Can we finally have type-safety for curry?

[millsp]

I tried this on the playground but it fails (Analyzation: SpreadElement)

Curry is very hard to type correctly, this would be the ultimate test for your project:

const curry = (fn) => {
    const fn0 = (...args) => {
      if (args.length >= fn.length)
        return fn(...args)
      return (...argsn) => fn0(...args, ...argsn)
    }

    return fn0
}

console.log(curry<X>((a: X, b: string, c: X) => [a, b, c], [])('1')(2)('3')) // ['1', 2, '3']

Do you think this could be type safe?

[JSMonk]

Hi @pirix-gh. For now, I don't know how to implement it safely, because we need to have some special collection type which will be converted to applied arguments. But, I don't say that this is impossible. Thank you for the question ^_^.

[millsp]

Hey @JSMonk, great job, anyway!

I think that you could pull this out with generics only:

const curry = <P, R>(fn: (...args: P) => R) => {
  const fn0 = <P0>(...args0: P0) => {
    if (args0.length >= fn.length)
      return fn(...args0)
      
    return <PN>(...argsn: PN) => fn0(...args0, ...argsn)
  }

  return fn0
}

But that really depends on how you do your flow analysis.

I'd really love, and all my fellow functional programmers, to have this one day!

[JSMonk]

Okay, we will try to implement it :3 Thank you for the proposal.