milo-macros is an internal crate which represents the core of Milo.
It leverages Rust's procedural macro, syn and quote crates to allow an easy definition of states and matchers for the parser.
To define a new macro, you have to define a new method which the following signature:
#[proc_macro]
pub fn new_macro(input: TokenStream) -> TokenStream {
TokenStream::new( /* ... */)
}Everything that is not included within the return value will not be present in the executed code. Macro performance is not important for runtime because macros are only evaluated at compile time.
The generate! macro also emits parser constants and internal byte lookup tables used by syntax validators. These tables are generated at compile time and are not public API.
To return a new code, leverage the quote! macro, while for parsing use the parse_macro_input! macro. Here's an example:
#[proc_macro]
pub fn char(input: TokenStream) -> TokenStream {
let character = parse_macro_input!(input as LitChar);
let byte = LitByte::new(c_uchar::try_from(character.value()).unwrap(), character.span());
TokenStream::from(quote! { #byte })
}