Newt Lang

Newt is a domain specific language that compiles to Typescript type code. Newt is not for general purpose programming, but rather for creating toys/abominations in the TS type system.

Language Guide

Fundamentally, Newt is designed to provide more ergonomics around conditional types.

Take, for instance the following typescript expression:

interface IdLabel {
  id: number
}

interface NameLabel {
  name: string
}

type IdOrNameLabel<T extends string | number> =
  T extends string 
  ? NameLabel 
  : IdLabel;

The same thing can be expressed in Newt using different control structures:

interface IdLabel {
  id: number
}

interface NameLabel {
  name: string
}

type IdOrNameLabel(T)
where T <: string | number
do
  if T <: string then
    NameLabel
  else
    IdLabel
  end
end

Or

type IdOrNameLabel(T)
where T <: string | number
do
  cond do
    T <: string -> NameLabel
    else -> IdLabel
  end
end

Or finally:

type IdOrNameLabel(T)
where T <: string | number
do
  match T do
    string -> NameLabel
    _ -> IdLabel
  end
end

While these simple examples probably aren't too compelling given all the extra characters, this get much more useful as your type programs get more complicated.

The easiest way to get started is to check out some of the examples or tests.

Development

Refer to ./mise.toml for all build, dev, and test commands.