[plt-scheme] the make-pipe

(module test-mem mzscheme
  (require (lib "process.ss"))
  (define null-port (open-output-file "/dev/null" 'append))
  (define null-iport (open-input-file "/dev/null"))
  (define std-oport (current-output-port))

  (define (x) (let-values ([(r w) (make-pipe)])
                (process/ports w null-iport null-port "/sbin/sysctl -a")
                (process/ports std-oport r  null-port "grep
vm.min_free_kbytes")
              ))
  (define (y) (process/ports std-oport null-iport null-port "/sbin/sysctl
-a| grep vm.min_free.kbytes"))
  (define (z)
    (let-values ([(r w) (make-pipe)])
      (process/ports w null-iport null-port "/sbin/sysctl -a")
      (let loop ()
        (let ([v (read-line r)])
          (if (eof-object? r)
              (void)
            (begin
              (fprintf std-oport "~a~n" v)
              (loop))
            )))))
  )

------------------------------------

Welcome to DrScheme, version 371.3-svn7nov2007 [3m].
Language: (module ...).
> (x)
(#f #f 11744 #f #<procedure:control>)
> (y)
(#f #f 11745 #f #<procedure:control>)
vm.min_free_kbytes = 5858

1.why (x) and (y) is different?
2. why (z) could not terminate?

Thanks
-- 
Gang
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