Trying to use the Cocoa example

My apologies for what is probably an easy question to answer but my 
Unix skills are not too hot! When I (require "COCOA"), I get the 
following error message:

 > Error: The module "PTY" was required while loading 
"/usr/local/src/ccl/examples/cocoa-listener.lisp".
 >        No file could be found for that module.
 > While executing: REQUIRE
 > Type :GO to continue, :POP to abort.
 > If continued: If "PTY" still hasn't been provided,
you will be asked to choose a file.
Type :? for other options.
1 > :pop

Which leaves me confused.

Thanks in advance,

-- 
Gary Warren King, Senior Research Fellow
EKSL, University of Massachusetts

"Everyday life is like programming, I guess, If you love something you 
can put beauty into it."
   -- Donald Knuth