Allow scoping in rule arguments

[Ondraceq]

Hi,
I'm trying to use parametrized rules with my own enum type (&[T]).
Problem is that when using parametrized rules, I cannot use scoping. I have managed to do a workaround, but it's really not ideal.
Here is the code with the workaround - and with what I think would be better way to be able to write it.

#[derive(Debug, Clone, PartialEq)]
pub enum MyEnum {
    Value,
}

const ENUM_VALUE: MyEnum = MyEnum::Value;

peg::parser! {
    grammar my_parser() for [MyEnum] {
        rule single(val:MyEnum) -> MyEnum = [v if v == val] { v }
        // pub rule value() -> MyEnum = single(MyEnum::Value) // error
        pub rule value() -> MyEnum = single(ENUM_VALUE)
    }
}

I'm using the "0.7.0" version from crates.io

[kevinmehall]

Thanks for pointing that out. As a better workaround, it should work if you wrap it in an extra set of parentheses: single((MyEnum::Value)).

The rule_arg() rule in the meta-grammar needs to be expanded to better cover Rust expressions. Right now it only accepts literals, variable names, and anything in parentheses.

[Ondraceq]

Thank you - I didn't know that the parenthesis will work.
This makes this issue low priority - maybe just mention it somewhere in the docs/examples.