Welcome to the CHICKEN Scheme pasting service

(import
  (chicken base)
  (chicken process)
  (chicken process-context)
  (chicken process-context posix)
  (chicken foreign)
  (chicken file posix)
  )

(foreign-declare "
  #include <sys/types.h>                 
  #include <sys/socket.h>")

(define make-socketpair
  (foreign-primitive ()
    "
    int ends[2] = { -1, -1 };
    socketpair(PF_LOCAL, SOCK_STREAM, 0, ends);
    C_word av[4] = { C_SCHEME_UNDEFINED, C_k, C_fix(ends[0]), C_fix(ends[1]) };
    C_values(4, av);
    "))

(define (write/flush data port)
  (write data port)
  (flush-output port))

(define (debug . args)
  (apply print (current-process-id) ": "  args))

(let-values (((p c) (make-socketpair)))

  (define datum (if (string=? (car (command-line-arguments)) "ok") '() #t))
  (print "datum is " datum)

  (define (child)
    (let ((out (open-output-file* c))
          (in  (open-input-file* c)))
      (debug "sleeping")
      (sleep 1)
      (debug "writing to parent")
      (write/flush datum out)
      (debug "bye")))

  (define (parent child)
    (let ((out (open-output-file* p))
          (in  (open-input-file* p)))
      (debug "reading from " child)
      (let ((got (read in)))
        (debug "got '" got "' - bye"))))

  (let ((pid (process-fork child #t)))
    (if (zero? pid)
      (exit)
      (parent pid))))

> ./parent-child nok
datum is #t
80693: reading from 80694
80694: sleeping
80694: writing to parent
80694: bye
load: 0.30  cmd: parent-child 80693 [sbwait] 5.64r 0.00u 0.00s 0% 8132k
load: 0.30  cmd: parent-child 80693 [sbwait] 5.82r 0.00u 0.00s 0% 8132k
load: 0.30  cmd: parent-child 80693 [sbwait] 5.95r 0.00u 0.00s 0% 8132k
load: 0.30  cmd: parent-child 80693 [sbwait] 6.10r 0.00u 0.00s 0% 8132k
^C⏎

> ./parent-child nok
datum is #t
80832: reading from 80833
80833: sleeping
80833: writing to parent
80833: bye
80832: got '#t' - bye