Higher-Order TypeScript (HOTScript)

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

🚧 work in progress 🚧

// 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
  ]
>;

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

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]

// 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;
};

TODO

• [ ] Function
  • [x] Pipe
  • [x] PipeRight
  • [x] Call
  • [x] Apply
  • [x] PartialApply
  • [x] Compose
  • [x] ComposeLeft
• [ ] Tuples
  • [ ] Zip
  • [x] Partition
  • [x] Sort
  • [x] Head
  • [x] At
  • [x] Tail
  • [x] Last
  • [x] FlatMap
  • [x] Find
  • [x] Sum
  • [x] Drop n
  • [x] Take n
  • [x] TakeWhile
  • [x] Join separator
  • [x] Map
  • [x] Filter
  • [x] Reduce
  • [x] ReduceRight
  • [x] Every
  • [x] Some
• [ ] Object
  • [x] Get
  • [x] FromEntries
  • [x] Entries
  • [x] MapValues
  • [x] MapKeys
  • [x] GroupBy
  • [x] Assign
  • [x] Pick
  • [x] PickBy
  • [x] Omit
  • [x] OmitBy
  • [x] CamelCase
  • [x] CamelCaseDeep
  • [x] SnakeCase
  • [x] SnakeCaseDeep
  • [x] KebabCase
  • [x] KebabCaseDeep
• [ ] Union
  • [x] Map
  • [x] Extract
  • [x] ExtractBy
  • [x] Exclude
  • [x] ExcludeBy
• [ ] String
  • [x] Length
  • [x] TrimLeft
  • [x] TrimRight
  • [x] Trim
  • [x] Join
  • [x] Replace
  • [x] Slice
  • [x] Split
  • [x] Repeat
  • [x] StartsWith
  • [x] EndsWith
  • [x] ToTuple
  • [x] ToNumber
  • [x] ToString
  • [x] Prepend
  • [x] Append
  • [x] Uppercase
  • [x] Lowercase
  • [x] Capitalize
  • [x] Uncapitalize
  • [x] SnakeCase
  • [x] CamelCase
  • [x] KebabCase
  • [x] Compare
  • [x] Equal
  • [x] NotEqual
  • [x] LessThan
  • [x] LessThanOrEqual
  • [x] GreaterThan
  • [x] GreaterThanOrEqual
• [ ] Number
  • [x] Add
  • [x] Multiply
  • [x] Subtract
  • [x] Negate
  • [x] Power
  • [x] Div
  • [x] Mod
  • [x] Abs
  • [x] Compare
  • [x] GreaterThan
  • [x] GreaterThanOrEqual
  • [x] LessThan
  • [x] LessThanOrEqual
• [ ] Boolean
  • [x] And
  • [x] Or
  • [x] Not
  • [x] Extends
  • [x] Equals
  • [x] DoesNotExtend