rustmacrosrust-macros

How can a macro match any token tree except comma


macro_rules! foo {
    ( $( $( $tok:tt )* ,)* ) => {
        [ bar!( $( $tok )* ,)* ]
    }
}

Produces error: local ambiguity when calling macro 'foo'. Because the comma ',' is of type :tt. I would need a way to match all token trees excluding the coma token.

Usage example

foo!(
    add t0 zero zero,
    add t1 t0 a0,
    lb t1 0(t1),
)

Should produce:

[
    bar!(add t0 zero zero),
    bar!(add t1 t0 a0),
    bar!(lb t1 0(t1)),
]

Solution

  • TT munching to the rescue!

    macro_rules! foo {
        (@accumulate [ $($accumulated:tt)* ] [ ]) => { [ $($accumulated)* ] };
        (@accumulate [ $($accumulated:tt)* ] [ $($this_line:tt)* ] , $($rest:tt)* ) => {
            foo! { @accumulate [
                $($accumulated)*
                bar!( $($this_line)* ),
            ] [] $($rest)* }
        };
        (@accumulate [ $($accumulated:tt)* ] [ $($this_line:tt)* ] $current:tt $($rest:tt)* ) => {
            foo! { @accumulate [ $($accumulated)* ] [ $($this_line)* $current ] $($rest)* }
        };
        ( $($t:tt)* ) => { foo! { @accumulate [] [] $($t)* } }
    }