Higher-Order TypeScript (HOTScript)

A lodash-like library for types, with support for type-level lambda functions.

🚧 work in progress 🚧

Installation

You can find HotScript on npm:

npm install -D hotscript

HotScript is a work-in-progress library, so expect breaking changes in its API.

Examples

Transforming a list

import { Pipe, Tuples, Strings, Numbers } from "hotscript";

// prettier-ignore
type res1 = Pipe<
  //  ^? 95
  [1, 2, 3, 4, 3, 4],
  [
    Tuples.Map<Numbers.Add<3>>,
    Tuples.Join<".">,
    Strings.Split<".">,
    Tuples.Map<Strings.ToNumber>,
    Tuples.Map<Numbers.Add<10>>,
    Tuples.Sum
  ]
>;

Defining a first-class function

import { Call, Fn Tuples } from "hotscript";

// This is a type-level "lambda"!
interface Duplicate extends Fn {
  return: [this["arg0"], this["arg0"]];
}

type result1 = Call<Tuples.Map<Duplicate>, [1, 2, 3, 4]>;
//     ^? [[1, 1], [2, 2], [3, 3], [4, 4]]

type result2 = Call<Tuples.FlatMap<Duplicate>, [1, 2, 3, 4]>;
//     ^? [1, 1, 2, 2, 3, 3, 4, 4]

Transforming an object type

// Let's compose some functions to transform an object type:
type ToAPIPayload<T> = Pipe<
  T,
  [
    Objects.OmitBy<Booleans.Equals<symbol>>,
    Objects.Assign<{ metadata: { newUser: true } }>,
    Objects.SnakeCaseDeep,
    Objects.Assign<{ id: string }>
  ]
>;
type T = ToAPIPayload<{
  id: symbol;
  firstName: string;
  lastName: string;
}>;
// Returns:
type T = {
  id: string;
  metadata: { new_user: true };
  first_name: string;
  last_name: string;
};