Function to exit the program without a panic?

[tryoxiss]

Is there a way to exit a gleam program or task without getting an error? You can panic as, but that gives an error. todo as gives both an error and warning. This is far from ideal if the exit was intentional and not due to an error (e.g., a graceful shutdown) If not, is there a reason, or could it be added?

If such a function is added, an assosiated type should be added, being simply a type with no variants - making it impossible to construct, clearly showing that the function will not return (simple demo implementation below)

import gleam/io

pub type Never {}

pub fn main() -> Never {
  io.println("Do Stuff")
  exit()
}

pub fn exit() -> Never {
  panic as "exited" // replace with the proper way to exit a program if there is one
}

[Enderchief]

What would be a use case for this?

Maybe FFI could work instead. Although I've heard early exits aren't the best for the Erlang VM.

// main.gleam
import gleam/io

pub fn main() {
  io.println("Hello!")
  exit(0)
  io.println("this never prints")
}

@external(erlang, "exit_ffi", "do_exit")
@external(javascript, "./exit_ffi.mjs", "do_exit")
pub fn exit(exit_code: Int) -> Nil

% exit_ffi.erl
-module(exit_ffi).
-export([do_exit/1]).

do_exit(Code) ->
  halt(Code).

// exit_ffi.mjs
export function do_exit(code) {
  if (globalThis.process) process.exit(code);
  else if (globalThis.Deno) Deno.exit(code);
  else throw Error; // if in the browser
}

[lpil]

I'd probably use init:stop rather than erlang:halt as it shuts down application trees

[tryoxiss]

What would be a use case for this?

Maybe FFI could work instead. Although I've heard early exits aren't the best for the Erlang VM.

// main.gleam
import gleam/io

pub fn main() {
  io.println("Hello!")
  exit()
  io.println("this never prints")
}

@external(erlang, "exit_ffi", "do_exit")
@external(javascript, "./exit_ffi.mjs", "do_exit")
pub fn exit(exit_code: Int) -> Nil

% exit_ffi.erl
-module(exit_ffi).
-export([do_exit/0]).

do_exit(Code) ->
  halt(Code).

// exit_ffi.mjs
export function do_exit(code) {
  if (globalThis.process) process.exit(code);
  else if (globalThis.Deno) Deno.exit(code);
  else throw Error; // if in the browser
}

The case I had in mind was a server which is expected to be running until an exit is called for, at which point it should finish outstanding I/O and close itself. You mentioned early exists are not good for the BEAM VM, is there a better way to do this instead then?

[lpil]

The case I had in mind was a server which is expected to be running until an exit is called for, at which point it should finish outstanding I/O and close itself.

Then you want init.stop, not erlang.halt

[tryoxiss]

The case I had in mind was a server which is expected to be running until an exit is called for, at which point it should finish outstanding I/O and close itself.

Then you want init.stop, not erlang.halt

Thank you!