TypeScript 3.9 | Advanced Types: Extracts inner types and return type from function

FunctionInfer.ts

export type FunctionInfer<F> =
  F extends (...args: infer A) => infer R
  ? [A, R]
  : never

const fn01 = (arg: number, foo: any) => arg === foo

export type Type1 = FunctionInfer<typeof fn01> // [[arg: number, foo: any], boolean]

// https://medium.com/free-code-camp/typescript-curry-ramda-types-f747e99744ab
// https://github.com/millsp/medium/blob/master/types-curry-ramda/src/index.ts