Generating TypeScript declaration files with Gleam

gleam_ts_gen.d.ts

import type * as $io from "../gleam_stdlib/gleam/io.d.mts";
import type * as _ from "./gleam.d.mts";

export class User extends _.CustomType {
  constructor(id: string, username: string, role: Role$);
  
  id: string;
  username: string;
  role: Role$;
}

export type User$ = User;

export class Default extends _.CustomType {}

export class Admin extends _.CustomType {}

export class Guest extends _.CustomType {}

export class Other extends _.CustomType {
  constructor(argument$0: string);
  
  0: string;
}

export type Role$ = Default | Admin | Guest | Other;

export function role_to_string(role: Role$): string;

export function make_admin(user: User$): _.Result<User$, any>;

export function print_role(user: User$): null;

gleam_ts_gen.gleam

import gleam/io


pub type User {
  User(id: String, username: String, role: Role)
}

pub type Role {
  Default
  Admin
  Guest
  Other(String)
}

pub fn role_to_string(role) {
  case role {
    Admin -> "admin"
    Default -> "default"
    Guest -> "Guest"
    Other(name)-> "Other(" <> name <> ")"
  }
}

pub fn make_admin(user) {
  // some business logic
  Ok(User(..user, role: Admin))
}

pub fn print_role(user: User) {
  user.role |> role_to_string |> io.println 
}

gleam_ts_gen.mjs

import * as $io from "../gleam_stdlib/gleam/io.mjs";
import { Ok, CustomType as $CustomType } from "./gleam.mjs";

export class User extends $CustomType {
  constructor(id, username, role) {
    super();
    this.id = id;
    this.username = username;
    this.role = role;
  }
}

export class Default extends $CustomType {}

export class Admin extends $CustomType {}

export class Guest extends $CustomType {}

export class Other extends $CustomType {
  constructor(x0) {
    super();
    this[0] = x0;
  }
}

export function role_to_string(role) {
  if (role instanceof Admin) {
    return "admin";
  } else if (role instanceof Default) {
    return "default";
  } else if (role instanceof Guest) {
    return "Guest";
  } else {
    let name = role[0];
    return ("Other(" + name) + ")";
  }
}

export function make_admin(user) {
  return new Ok(user.withFields({ role: new Admin() }));
}

export function print_role(user) {
  let _pipe = user.role;
  let _pipe$1 = role_to_string(_pipe);
  return $io.println(_pipe$1);
}