guile filter output via an external command

gistfile1.scm

(use-modules (ice-9 rdelim))

(define (filter inproc outproc cmd . args)
  "filter the output of inproc via cmd to outproc through an external cmd"
  (let* ((read-pipe (pipe))
         (read-in  (car read-pipe))
         (read-out  (cdr read-pipe))
         (write-pipe (pipe))
         (write-in  (car write-pipe))
         (write-out  (cdr write-pipe))
         (child-pid    (primitive-fork)))
    (if (= child-pid 0)
        (begin
          (close-output-port read-out)
          (close-input-port write-in)
          (dup2 (fileno read-in) 0)
          (dup2 (fileno write-out) 1)
          (apply execlp (append (list cmd) (append (list cmd) args))))
        (begin
          (close-input-port read-in)
          (close-output-port write-out)
          (parameterize ((current-output-port read-out))
            (inproc))
          (close-output-port read-out)
          (parameterize ((current-input-port write-in))
            (outproc))
          (close-input-port write-in)
          (waitpid child-pid 0)))))

; To use
> (filter
    (lambda()
      (display "Hello World!")(newline))
    (lambda()
      (let loop ((line (read-line)))
        (if (not  (eof-object? line))
          (begin
            (write-line line)
            (loop (read-line))))))
    "sed" "s/World/Planet/")
Hello Planet!
$4 = (3892 . 0)
>