Crate deno_proc_macro_rules
source ·Expand description
macro_rules
-style syntax matching for procedural macros.
This crate is work-in-progress, incomplete, and probably buggy!
Example:
use proc_macro_rules::rules;
use proc_macro2::TokenStream;
fn main() {
let tokens: TokenStream = /* ... */;
rules!(tokens => {
($finish:ident ($($found:ident)*) # [ $($inner:tt)* ] $($rest:tt)*) => {
for f in found {
do_something(&finish, f, &inner, &rest[0]);
}
}
(foo $($bar:expr)?) => {
match bar {
Some(e) => foo_with_expr(e),
None => foo_no_expr(),
}
}
});
}
Import the rules
macro with use proc_macro_rules::rules
, then use with
rules!(tokens => { branches });
where tokens
is an expression which
evaluates to a TokenStream
(such as the argument in the definition of a
procedural macro).
Each branch in branches
should have the form ( pattern ) => { body }
where
pattern
is a macro-rules-style pattern (using all the same syntax for
meta-variables, AST nodes, repetition, etc.) and body
is rust code executed
when the pattern is matched. Within body
, any meta-variables in the pattern
are bound to variables of an appropriate type from either the
proc_macro2 or
syn crates. Where a meta-variable is
inside a repetition or option clause, it will be wrapped in a Vec
or
Option
, respectively.
For example, in the first branch in the above example ident
has type
syn::Ident
and inner
has type Vec<proc_macro2::TokenTree>
.