Suggestion: recursive pipe / compose types

[babakness]

Hi, I did some work recently on the Pipe and Compose types. I have an approach that uses a recursive type to deliver better typings on composed functions. For example, parameter names are preserved.

Here is a link the repo with the types

https://github.com/babakness/pipe-and-compose-types

Here is a link to the implementation:

https://github.com/babakness/pipe-and-compose

Related article:

https://dev.to/babak/introducing-the-recursive-pipe-and-compose-types-3g9o

--

There is good reason to keep the these types in an external repo. TypeScript's compiler seems treat them better that way.

All the best.

[gcanti]

@babakness thanks for sharing

p.s.

FYI Looks like there's some issue with polymorphic functions

import { head } from 'fp-ts/lib/Array'
import { pipe } from 'fp-ts/lib/function'
import { lift } from 'fp-ts/lib/Functor'
import { option } from 'fp-ts/lib/Option'

const toPair = <A>(a: A): [A, A] => [a, a]

const liftedToPair = lift(option)(toPair)

// f: <A>(a: A[]) => Option<[A, A]>
const f = pipe(
  head,
  liftedToPair
)

import { pipe as pipe2 } from 'pipe-and-compose'

// f2: (as: {}[]) => Option<[{}, {}]>
const f2 = pipe2(head, liftedToPair)

[babakness]

@gcanti thanks for noticing this. I see that as of the latest TS 3.4+, overloading pipe and compose without variadic support are now supported by the compiler. Variadic support is not there:

microsoft/TypeScript#30727

I believe the support needed by the compiler for a recursive version such as mine is for infer to work with generics. The recursive type depends on these helpers

/**
 * Extracts function arguments
 */
export type ExtractFunctionArguments < Fn > = Fn extends  ( ...args: infer P ) => any  ? P : never

/**
 * Extracts function return values
 */
export type ExtractFunctionReturnValue<Fn> = Fn extends  ( ...args: any[] ) => infer P  ? P : never

I'll keep an eye out for this. I created a feature request for this at TypeScript's repo:

microsoft/TypeScript#30887

[EricCrosson]

The linked issue microsoft/TypeScript#30887 closed 8 days ago 👀

Does this mean we're unblocked in terms of offering a compose function with fp-ts?