macro_rules! def_parser {
{ } => { ... };
{ $lt:lifetime } => { ... };
{ $vis:vis $name:ident [$I:path] ($input:ident) -> $output:ty $(where $($tn:path: $wt:path),+)? $b:block } => { ... };
{ $vis:vis $name:ident $(<$($lt:lifetime),*>)? ($input:ident: $it:ty ) -> $output:ty $b:block } => { ... };
}
Unfinished
Define a Parser with data like a function