How are types converted between Erlang and Gleam

[upper laurel]

Firstly, I the only time i ever wrote Erlang code is the snipped ill present:

-type result() :: {foo, [string]} | bar.

readlines(FileName) ->
    case file:open(FileName, [read]) of
        {ok, Device} ->
            try
                Content = get_all_lines(Device),
                {foo, Content}
            after
                file:close(Device)
            end;
        {error, Reason} ->
            bar
            % []
    end.

Given this Erlang code and this Gleam type:

type ErlangResult {
  Bar
  Foo(List(String))
}

it appears to magically work. Is there some ressource (maybe its how types are represented in the BEAM?) for which I can learn more about type conversions and what works when?

[full socket]

The type annotation for your Erlang function isn’t correct there

It says it returns a list of the atom “string”

When you want it to be binary()

Erlang types are not checked in any way by Gleam so you could put anything you want as the Erlang type and it’s be OK

The Gleam type is incorrect because- it may not be valid unicode so it should be BitArray

As for conversions; there are none! Whatever your external code returns is used as-is, so it’s really important that your annotations are accurate

[upper laurel]

Yeah I realised I dont even need the type in Erlang. I came to learn gleam, but now I wanna learn both haha

[upper laurel]

just realised that too. I converted it from this custom type to a "normal" result, wich seams to pair super well with standard erlang

[full socket]

Erlang is cool

[upper laurel]

yeah I know, but for my understanding. The gleam "Ok(...)" would be converted to a {ok, ...}?

[full socket]

Nothing is converted, that’s the same thing in the syntax of each language

[upper laurel]

its probably the representation in the beam, so i might look that up?