getting pipes going

[Johan Hidding]

Hi everyone,
I'm having difficulties getting (open-pipe ...) to work for me. I
would expect the following code:

(use-modules (ice-9 popen))

(display (with-output-to-string (lambda ()
           (let ((P (open-pipe "cat" OPEN_WRITE)))
             (display "Hello World!\n" P)
             (close-pipe P)))))

to output: Hello World!
But it gives me nothing, using guile-2.0.5. What's going wrong? I
would love to see some examples on how pipes are "supposed to be"
used.
Cheers, Johan