[clisp-list] Problem capturing output of ext:run-program using with-output-to-string

[Mirko V. <mir...@gm...>]

Hello,

I am trying to capture the output of ext:run-program.  I am running
clisp on windows+cywgin+emacs+slime
Running the plain command
> (ext:run-program  "ls" :arguments '("-la" "/bin"))
give me the correct output in the *inferior-lisp* buffer

However, when I try to capture the output using `with-output-to-string':
CL-USER> (with-output-to-string (s)
   (ext:run-program  "ls" :arguments '("-la" "/bin") :output s))
I get an error:
STRING: argument #1=#<OUTPUT STRING-OUTPUT-STREAM> should be a string,
a symbol or a character
   [Condition of type SIMPLE-TYPE-ERROR]

This is the first time I use `with-output-string', and I am copying
this usage almost verbatim from a slime mailing list thread (but
dealing with CMUCL).

Thank you

Mirko