Good way to handle NifRresult (Ruslter) in gleam

[RudolfVonKrugstein]

Hi,

I am trying to around with interfacing Rustler and Gleam.

One thing I noticed is, that it is not simple to handle a NifResult as a Result in Gleam.

I have a function in Rust that returns a Nif Result.

fn some_func() -> NifResult<String> {...}

Using it as a Nif in erlang:

-module(native)
-export([some_func/0])
-nifs([some_func/0])

some_func() ->
  exit(nif_library_not_loaded).

And using it in gleam:

@external(erlang, "native", "some_fun")
pub fn some_func() -> Result(String, Dynamic)

Trying round with this, like this:

let assert Ok(val) = some_func()

It seems to me, that this works for errors but not for "Ok" Values.

Looking at some similar code in Elixir: https://github.com/elixir-nx/ortex/blob/main/lib/ortex/model.ex#L25

It seems to me (and I might be wrong), that NifResult in Erlang/Elixir results in {:error, error_val} vor an Error but in just ok_val if there is no error (and not in {:ok, ok_val}).
This does not properly get converted (as far as I can tell) to gleams Result for the OK case.

I did not find any example, where a NifResult is used in Gleam and I am unsure how to do it. Can I even somehow represent a value, that can be {:error, error_val} or ok_val in Gleam?

Any advice on how to write a ffi when Returning NifResult from Rust(ler)?

Thank you!

[lpil]

Untagged unions are not representable in Gleam, you will need to call that function from Erlang and then convert it to a Gleam result.