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

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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

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