functors.ts

// https://medium.com/@gcanti/higher-kinded-types-in-typescript-static-and-fantasy-land-d41c361d0dbe

import {
  TypeConstructors,
  TypeConstructors2,
  Kind,
  Kind2,
} from "./higherKindedTypes";

export interface Functor<F extends TypeConstructors, A> {
  map: <A1>(f: (a: A) => A1) => Kind<F, A1>;
}

export interface Functor2<F extends TypeConstructors2, A, B> {
  map: <A1>(f: (a: A) => A1) => Kind2<F, A1, B>;
}

hkt.ts

// Inspired by https://medium.com/@gcanti/higher-kinded-types-in-typescript-static-and-fantasy-land-d41c361d0dbe
/**
 * `* -> *` constructors
 */
export interface HigherKindedType<TypeConstructor, TypeParameter> {
  readonly _TypeConstructor: TypeConstructor;
  readonly _TypeParameter: TypeParameter;
}

/**
 * `* -> * -> *` constructors
 */
export interface HigherKindedType2<
  TypeConstructor,
  TypeParameter1,
  TypeParameter2
> {
  readonly _TypeConstructor: TypeConstructor;
  readonly _TypeParameter1: TypeParameter1;
  readonly _TypeParameter2: TypeParameter2;
}

/*
 * Type level dictionaries for HigherKindedTypes: TypeConstructor -> concrete type
 */
/* eslint-disable @typescript-eslint/no-empty-interface */
export interface TypeConstructorToHigherKindedType<A> {}
/* eslint-enable @typescript-eslint/no-empty-interface */

/* eslint-disable @typescript-eslint/no-empty-interface */
export interface TypeConstructorToHigherKindedType2<A, B> {}
/* eslint-enable @typescript-eslint/no-empty-interface */

/* eslint-disable @typescript-eslint/no-explicit-any */
export type TypeConstructors = keyof TypeConstructorToHigherKindedType<any>;
/* eslint-enable @typescript-eslint/no-explicit-any */

/* eslint-disable @typescript-eslint/no-explicit-any */
export type TypeConstructors2 = keyof TypeConstructorToHigherKindedType2<
  any,
  any
>;
/* eslint-enable @typescript-eslint/no-explicit-any */

/* eslint-disable @typescript-eslint/no-explicit-any */
export type Kind<
  TypeConstructor extends TypeConstructors,
  A
> = TypeConstructor extends TypeConstructors
  ? TypeConstructorToHigherKindedType<A>[TypeConstructor]
  : any;
/* eslint-enable @typescript-eslint/no-explicit-any */

/* eslint-disable @typescript-eslint/no-explicit-any */
export type Kind2<
  TypeConstructor extends TypeConstructors2,
  A,
  B
> = TypeConstructor extends TypeConstructors2
  ? TypeConstructorToHigherKindedType2<A, B>[TypeConstructor]
  : any;
/* eslint-enable @typescript-eslint/no-explicit-any */