Gleam: Annotating return types on anonymous functions

[edkelly303]

I just installed Gleam v0.7.0 and have been playing with it this afternoon - it's really fun, thanks so much for making it! As a big Elm fan, I've been wanting a similarly friendly statically typed language on the Beam for ages.

I have an anonymous function where I've annotated the type of the argument as follows:

pub fn example(x: Int) -> Int {
  let anon = fn(y: Int) {
    1 + y
  } 
  anon(x)
}

However, if I also try to annotate the return type:

pub fn example(x: Int) -> Int {
  let anon = fn(y: Int) -> Int {
    1 + y
  } 
  anon(x)
}

I get:

error: Syntax error

let anon = fn(y: Int) -> Int {
                      ^^ Unexpected token

Expected one of "{"

I'm not sure if this is expected behaviour? It seems unintuitive to be able to annotate the arguments of an anonymous function but not the return type.

[lpil]

No specific reason why we don't have this, just an unimplemented feature! This would be a good one to get in the next release.