It's real old and out of date now, but the STD grammar of Perl 6 was written in Perl 6 ahead of time and the Pugs implementation worked against it https://github.com/perl6/std/blob/master/STD.pm6

Rakudo (the current major Perl 6 compiler) also uses grammars to actually parse Perl 6 programs, but from the bootstrap language NQP https://github.com/rakudo/rakudo/blob/master/src/Perl6/Gramm...