Higher-Order TypeScript (HOTScript)

A library of composable functions for the type level!

Transform your TypeScript types in any way you want using functions you already know.

Features

• Type-level higher-order functions (Tuples.Map, Tuples.Filter, Objects.MapValues, etc).
• Type-level pattern matching with Match.
• Performant math operations (Numbers.Add, Numbers.Sub, Numbers.Mul, Numbers.Div, etc).
• Custom "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

Run this as a TypeScript Playground

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

type res1 = Pipe<
  //  ^? 62
  [1, 2, 3, 4],
  [
    Tuples.Map<Numbers.Add<3>>,       // [4, 5, 6, 7]
    Tuples.Join<".">,                 // "4.5.6.7"
    Strings.Split<".">,               // ["4", "5", "6", "7"]
    Tuples.Map<Strings.Prepend<"1">>, // ["14", "15", "16", "17"]
    Tuples.Map<Strings.ToNumber>,     // [14, 15, 16, 17]
    Tuples.Sum                        // 62
  ]
>;

Defining a first-class function

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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

Run this as a TypeScript Playground

import { Pipe, Objects, Booleans } from "hotscript";

// 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;
};

Parsing a route path

Run this as a TypeScript Playground

https://user-images.githubusercontent.com/2315749/222081717-96217cd2-ac89-4e06-a942-17fbda717cd2.mp4

import { Pipe, Objects, Strings, ComposeLeft, Tuples, Match } from "hotscript";

type res5 = Pipe<
  //    ^? { id: string, index: number }
  "/users/<id:string>/posts/<index:number>",
  [
    Strings.Split<"/">,
    Tuples.Filter<Strings.StartsWith<"<">>,
    Tuples.Map<ComposeLeft<[Strings.Trim<"<" | ">">, Strings.Split<":">]>>,
    Tuples.ToUnion,
    Objects.FromEntries,
    Objects.MapValues<
      Match<[Match.With<"string", string>, Match.With<"number", number>]>
    >
  ]
>;

API

• Core
  • Pipe<Input, Fn[]>
  • PipeRight<Fn[], Input>
  • Call<Fn, ...Arg>
  • Apply<Fn, Arg[]>
  • PartialApply<Fn, Arg[]>
  • Compose<Fn[]>
  • ComposeLeft<Fn[]>
• Function
  • ReturnType<Fn>
  • Parameters<Fn>
  • Parameter<N, Fn>
  • MapReturnType<Fn, FunctionType>
  • MapParameters<Fn, FunctionType>
• Tuples
  • Create<X> -> [X]
  • Partition<Tuple>
  • IsEmpty<Tuple>
  • Zip<...Tuple[]>
  • ZipWith<Fn, ...Tuple[]>
  • Sort<Tuple>
  • Head<Tuple>
  • Tail<Tuple>
  • At<N, Tuple>
  • Last<Tuple>
  • FlatMap<Fn, Tuple>
  • Find<Fn, Tuple>
  • Drop<N, Tuple>
  • Take<N, Tuple>
  • TakeWhile<Fn, Tuple>
  • GroupBy<Fn, Tuple>
  • Join<Str, Tuple>
  • Map<Fn, Tuple>
  • Filter<Fn, Tuple>
  • Reduce<Fn, Init, Tuple>
  • ReduceRight<Fn, Init, Tuple>
  • Reverse<Tuple>
  • Every<Fn, Tuple>
  • Some<Fn, Tuple>
  • SplitAt<N, Tuple>
  • ToUnion<Tuple>
  • ToIntersection<Tuple>
  • Prepend<X, Tuple>
  • Append<X, Tuple>
  • Concat<T1, T2>
  • Min<Tuple>
  • Max<Tuple>
  • Sum<Tuple>
• Object
  • Readonly<Obj>
  • Mutable<Obj>
  • Required<Obj>
  • Partial<Obj>
  • ReadonlyDeep<Obj>
  • MutableDeep<Obj>
  • RequiredDeep<Obj>
  • PartialDeep<Obj>
  • Update<Path, Fn | V, Obj>
  • Record<Key, Value>
  • Keys<Obj>
  • Values<Obj>
  • AllPaths<Obj>
  • Create<Pattern, X>
  • Get<Path, Obj>
  • FromEntries<[Key, Value]>
  • Entries<Obj>
  • MapValues<Fn, Obj>
  • MapKeys<Fn, Obj>
  • Assign<...Obj>
  • Pick<Key, Obj>
  • PickBy<Fn, Obj>
  • Omit<Key, Obj>
  • OmitBy<Fn, Obj>
  • CamelCase<Obj>
  • CamelCaseDeep<Obj>
  • SnakeCase<Obj>
  • SnakeCaseDeep<Obj>
  • KebabCase<Obj>
  • KebabCaseDeep<Obj>
• Union
  • Map<Fn, U>
  • Extract<T, U>
  • ExtractBy<Fn, U>
  • Exclude<T, U>
  • ExcludeBy<Fn, U>
  • NonNullable<U>
  • ToTuple<U>
  • ToIntersection<U>
• String
  • Length<Str>
  • TrimLeft<Str>
  • TrimRight<Str>
  • Trim<Str>
  • Join<Sep, Str>
  • Replace<From, To, Str>
  • Slice<Start, End, Str>
  • Split<Sep, Str>
  • Repeat<N, Str>
  • StartsWith<S, Str>
  • EndsWith<E, Str>
  • ToTuple<Str>
  • ToNumber<Str>
  • ToString<Str>
  • Prepend<Start, Str>
  • Append<End, Str>
  • Uppercase<Str>
  • Lowercase<Str>
  • Capitalize<Str>
  • Uncapitalize<Str>
  • SnakeCase<Str>
  • CamelCase<Str>
  • KebabCase<Str>
  • Compare<Str, Str>
  • Equal<Str, Str>
  • NotEqual<Str, Str>
  • LessThan<Str, Str>
  • LessThanOrEqual<Str, Str>
  • GreaterThan<Str, Str>
  • GreaterThanOrEqual<Str, Str>
• Number
  • Add<N, M>
  • Multiply<N, M>
  • Subtract<N, M>
  • Negate<N>
  • Power<N, M>
  • Div<N, M>
  • Mod<N, M>
  • Abs<N>
  • Compare<N, M>
  • GreaterThan<N, M>
  • GreaterThanOrEqual<N, M>
  • LessThan<N, M>
  • LessThanOrEqual<N, M>
• Boolean
  • And<Bool, Bool>
  • Or<Bool, Bool>
  • XOr<Bool, Bool>
  • Not<Bool>
  • Extends<A, B>
  • Equals<A, B>
  • DoesNotExtend<A, B>