todo msg vs todo as msg

[sobolevn]

Currently you can write:

fn testfn() {
  todo "msg"
}

pub fn main() {
  testfn()
}

It will produce: Error: This has not yet been implemented

And you can write:

fn testfn() {
  todo as "msg"
}

pub fn main() {
  testfn()
}

Which will produce Error: msg as expected.
It parses as:

[
    Expression(
        Todo {
            kind: Keyword,
            location: SrcSpan {
                start: 1,
                end: 5,
            },
            message: None,
        },
    ),
    Expression(
        String {
            location: SrcSpan {
                start: 6,
                end: 12,
            },
            value: "text",
        },
    ),
]

So, just two expressions: one after another.

The same happens with panic.

It looks like this might be a common place for errors.
That's why I propose to discuss:

• Is it really a common place for errors? I made this error myself. Was very surprised to see that the error message was different
• Is it worth it to change this to be a parse error? this is a breaking change on paper, but is it really in real life? Are there any real usages of todo near the next meaningful expression?

If we decide to make this an error, I have a PR ready :)

[lpil]

Gleam is not a whitespace sensitive language so todo msg is a todo followed by the variable msg. If you run the formatter it'll be formatted like so:

fn testfn() {
  todo
  "msg"
}

[sobolevn]

Yes :)
I understand that, that's why I attached the generated AST for this case.
I am asking if this code is actually useful for anything productive?

Code after todo should not be executed, so in this case "msg" will be unreachable and useless. Are there any other cases where todo "msg" might do something in a real-life use-case?

[giacomocavalieri]

The way I see it, Todo is for rapidly prototyping, adding warnings for unreachable code after a todo wouldn't be helpful since we already emit a warning for the todo itself. Rust does it and I always found it a bit annoying because I just get double the warnings for no real gain.

I think it's really common to have a todo followed by some valid expression, I do it all the time when prototyping things :)

[inoas]

I like todo as string.inspect(my_var) (or pprint.inspect)