weird read-line halting

gistfile1.sls

#lang racket
(require rackunit
         "main.rkt")
(provide tea-eval auto-cleanup-process)

;; tea-eval : SExp -> (list String String)
;; the first string is (hopefully) the output
;; the second string is the full output of the command, check this if the first
;; doesn't make any sense
(define (tea-eval sexp)
  (auto-cleanup-process
   (lambda (p out in err)
     (write-string (string-append
                    ;; BROKEN: should refernece local file's
                    ;; directory
                    (file->string "environment.js") ;; bunch of JavaScript code
                    "\nEnvironmentModule(this);\n\n"
                    (tea->js sexp)) ;; '(+ 1 2) => "a0(1, 2);\n" and '(define x 3) => "var x = 3;\n"
                   in)
     (flush-output in) ;; otherwise it seems to hang before this line
     (read-line err) ;; skip the Rhino header
     (read-line err))
   "/usr/bin/env"
   "rhino"))

(define-syntax auto-cleanup-process
  (syntax-rules ()
    [(_ procedure command args ...)
     (begin
       (let-values ([(a-subprocess stdout stdin stderr)
                     (subprocess #f #f #f command args ...)])
         (let ([value (procedure a-subprocess stdout stdin stderr)])
           (subprocess-kill a-subprocess #t)
           (close-input-port stdout)
           (close-input-port stderr)
           (close-output-port stdin)
           value)))]))


;; Below is a REPL session.
> (require "eval.rkt")
> (tea-eval '(+ 1 2))
"js>   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   >   > js> js> js> js> 3"
> (tea-eval '(define x 3))

danking@danking-desktop:~ 22:48 $ rhino
Rhino 1.7 release 2 2010 09 15
js> var x = 3;
js>