[plt-scheme] Parsers, parsers, and more parsers

Hi all,

I have a project that calls for a parser. The language has a syntax that 
requires at least four character look-ahead in some places (it's been 
around a while, and extended in a variety of ways). A Parsec parser was 
written as an exploration in Haskell, but we're not sure that Haskell is 
the way to go for the entire compiler for a variety of reasons that have 
been discussed and thought through by the group.

That said, what parsers are floating around for PLT Scheme? I'm aware of 
the Lexx/Yacc tools, and the Packrat framework that TonyG put together, 
which I've begun experimenting with. Are there any others out there that 
might be of use?

Many thanks,
Matt