Allow 'input lifetime parameter for token definitions.

[sandeep-datta]

Note the following code does not compile because of 'input. Please consider allowing this use case.

#[derive(Clone)]
pub enum Token<'input> {
    Open,
    Number(i32),
    Comma,
    Close,
    Ident(&'input str)
}

peg::parser!{
    grammar tokenparser() for [Token<'input>] {
          ...
    }
}

[kevinmehall]

I think this was fixed by #254 -- does this work?

peg::parser!{
    grammar tokenparser<'a>() for [Token<'a>] {
          ...
    }
}

[sandeep-datta]

It just creates a separate lifetime ...
pub fn module_traced<'input, 'a>(__input: &'input Input<'a>, module_name: &str) -> ::std::result::Result<Ast<'input>, ::peg::error::ParseError<PositionRepr<'a>>>

Also the following does not work either ....

peg::parser!{
    grammar tokenparser<'input>() for [Token<'input>] {
          ...
    }
}

"lifetime name 'input declared twice in the same scope"

[kevinmehall]

Hmm, so the problem is that you want to produce a result containing &'input Token<'a> without requiring the result type to have both lifetime params?

Ideally I'd like to get rid of the magic 'input lifetime since hard-coding a name violates macro hygiene and reduces flexibility in places like this, but I'm not sure how to do it without fully exposing the &'input part of the input type and making everyone write grammar foo<'input> for &'input str for the common case.

[sandeep-datta]

I might have had a brief mental lapse here. I conflated the lifetime of the token stream with the lifetime of the string used to generate it.

Regardless, I like your explicit lifetime syntax. Maybe you can elide the lifetime when the grammar does not reference it?