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: [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]

// 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

• Core
  • Pipe
  • PipeRight
  • Call
  • Apply
  • PartialApply
  • Compose
  • ComposeLeft
• Function
  • ReturnType
  • Parameters
  • Parameter n
• Tuples
  • Create
  • Partition
  • IsEmpty
  • Zip
  • ZipWith
  • Sort
  • Head
  • At
  • Tail
  • Last
  • FlatMap
  • Find
  • Sum
  • Drop n
  • Take n
  • TakeWhile
  • Join separator
  • Map
  • Filter
  • Reduce
  • ReduceRight
  • Every
  • Some
  • ToUnion
• Object
  • Readonly
  • Mutable
  • Required
  • Partial
  • ReadonlyDeep
  • MutableDeep
  • RequiredDeep
  • PartialDeep
  • Update
  • Record
  • Keys
  • Values
  • AllPaths
  • Create
  • Get
  • FromEntries
  • Entries
  • MapValues
  • MapKeys
  • GroupBy
  • Assign
  • Pick
  • PickBy
  • Omit
  • OmitBy
  • CamelCase
  • CamelCaseDeep
  • SnakeCase
  • SnakeCaseDeep
  • KebabCase
  • KebabCaseDeep
• Union
  • Map
  • Extract
  • ExtractBy
  • Exclude
  • ExcludeBy
• String
  • Length
  • TrimLeft
  • TrimRight
  • Trim
  • Join
  • Replace
  • Slice
  • Split
  • Repeat
  • StartsWith
  • EndsWith
  • ToTuple
  • ToNumber
  • ToString
  • Prepend
  • Append
  • Uppercase
  • Lowercase
  • Capitalize
  • Uncapitalize
  • SnakeCase
  • CamelCase
  • KebabCase
  • Compare
  • Equal
  • NotEqual
  • LessThan
  • LessThanOrEqual
  • GreaterThan
  • GreaterThanOrEqual
• Number
  • Add
  • Multiply
  • Subtract
  • Negate
  • Power
  • Div
  • Mod
  • Abs
  • Compare
  • GreaterThan
  • GreaterThanOrEqual
  • LessThan
  • LessThanOrEqual
• Boolean
  • And
  • Or
  • XOr
  • Not
  • Extends
  • Equals
  • DoesNotExtend