Depends on what you mean by parsing.

For simple string search kind of applications the following might work:
http://download.plt-scheme.org/doc/103p1/html/mzscheme/node115.htm

For push down automata:
http://docs.plt-scheme.org/parser-tools/index.html

It all comes down to whether your parsing language is a "regular" language or you need a stack to parse it (like if you have to look for matching braces etc)

--chandra