[plt-scheme] using parser-tools for stream parsing

The parser-tools collection seems to require an (end ...) specifier in a 
way that prevents online parsing of streams. I'd like to be write a 
parser that reads individual expressions one at a time from an input 
port without requiring each expression to be terminated with an EOF or 
even any particular token, and this seems impossible. Am I missing 
something?

Thanks,
Dave