The following Gleam code compiles to invalid Erlang code. The problem is due to the guard expression and the presence of a function in the type being compared.
The comparison works as expected if the equality check is done directly, i.e. foo == hello_greeting_wrapper.
Note that everything works correctly when targeting JavaScript, this is an Erlang-specific issue.
type GreetingWrapper {
GreetingWrapper(greeting_fn: fn() -> String)
}
fn hello_greeting() {
"Hello!"
}
const hello_greeting_wrapper = GreetingWrapper(hello_greeting)
fn is_hello(foo: GreetingWrapper) {
case foo {
f if f == hello_greeting_wrapper -> True
_ -> False
}
}
pub fn main() {
is_hello(hello_greeting_wrapper)
}
The output from gleam run is:
Compiling bug_repro
/bug_repro/build/dev/erlang/bug_repro/_gleam_artefacts/bug_repro.erl:16:41: illegal guard expression
% 16| F when F =:= {greeting_wrapper, fun hello_greeting/0} ->
% | ^
error: Shell command failure
There was a problem when running the shell command `escript`.
The following Gleam code compiles to invalid Erlang code. The problem is due to the guard expression and the presence of a function in the type being compared.
The comparison works as expected if the equality check is done directly, i.e.
foo == hello_greeting_wrapper
.Note that everything works correctly when targeting JavaScript, this is an Erlang-specific issue.
The output from
gleam run
is:Tested on Gleam v1.1.0 on macOS.