#lang racket/base

(define channel (make-channel))

(define (build-worker)
   (thread
    (λ ()
      (let loop ()
        (with-handlers
         ((exn:fail?
           (λ (e)
             (display (exn-message e))
             (newline)
             (channel-put channel e))))
         (let ((proc (channel-get channel))) (proc)))
        (loop)))))

(define (build-dispatch (num-workers 4))
   (define workers (build-list num-workers (build-worker)))
   (define (replace-dead!)
     (set! workers
       (map
        (λ (worker) (if (thread-dead? worker) (build-worker) worker))
        workers)))
   (define (dispatch proc) (replace-dead!) (channel-put channel proc))
   dispatch)

(provide build-dispatch)