the re2c ebuild depends on byacc, which is plain wrong. It includes 'bootsrap' files, so no lexer is needed.
at several points in the past we'd had patches to the bootstrap files, so byacc was used in those cases. Just because we don't use it in the latest release, doesn't mean we won't in future. However I have revised the DEPEND structure of the latest version, to reflect things better.