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minimal hkt in ts
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| export type Fn = (...x: never[]) => unknown | |
| export declare const _: unique symbol | |
| export type _ = typeof _ | |
| export declare abstract class Kind<F extends Fn = Fn> { | |
| abstract readonly [_]: unknown | |
| f: F | |
| } | |
| export type Input<F extends Kind> = F extends { f: (x: infer X) => any } | |
| ? X | |
| : unknown | |
| export type pipe<T extends Kind[], X> = T extends [ | |
| infer Head extends Kind, | |
| ...infer Tail extends Kind[], | |
| ] | |
| ? [X] extends [never] | |
| ? never | |
| : pipe<Tail, apply<Head, cast<X, Input<Head>>>> | |
| : X | |
| export type cast<T, U> = T extends U ? T : U | |
| export type apply<F extends Kind, X extends Input<F>> = ReturnType< | |
| (F & { | |
| readonly [_]: X | |
| })["f"] | |
| > | |
| // Example | |
| interface CapitalizeKind extends Kind { | |
| f(x: cast<this[_], Record<string, unknown>>): { | |
| [key in keyof typeof x as Capitalize<key & string>]: (typeof x)[key] | |
| } | |
| } | |
| interface OptionalKind extends Kind { | |
| f(x: cast<this[_], Record<string, unknown>>): { | |
| [key in keyof typeof x]?: (typeof x)[key] | |
| } | |
| } | |
| export interface First extends Kind { | |
| f(x: cast<this[_], unknown[]>): typeof x extends [] ? never : (typeof x)[0] | |
| } | |
| type result = pipe<[OptionalKind, CapitalizeKind], { hi: "there"; age: 5 }> | |
| type lha = apply<OptionalKind, { hi: "there" }> | |
| type asdf = apply<First, [1, 2, 3]> |
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