[plt-scheme] Examples of language implementation

Hi all,

I'm probably missing something obvious since this seems it should be  
easy to find, but searching isn't turning up what I'm after:  where  
are some good (and reasonably simple) examples I can peruse for  
creating languages and using them in mzscheme via #lang?  I've found  
one message from the mailing lists that's similar to what I'm looking  
for:
	http://list.cs.brown.edu/pipermail/plt-dev/2009-April/000573.html
(however, the info there doesn't give me quite enough context to use  
it in mzscheme from the command line, since it gives me a "collection  
not found" error for the language when I have the .ss file  
implementing the language in the same directory as the one using it...)

Thanks,
jmj