Steel Bank Common Lisp

Hello,

I have run across the following:

1. I wanted to write a small REPL in this form

(loop do (format t "~&~%Choice: ")
	until (string-equal (read-line) "quit"))

Unfortunately, "Choice:" is printed here only after the input is read.
Inserting (force-output) or (clear-output) after (format ...) did not help.
Changing "Choice:" to "Choice:~%" did help, but how could I make it work
without the newline?

2. I encountered an error on MAC OS X (sbcl-0.8.9) when trying to send
commands to the graphic program Data Explorer.  The same program works on
Linux without problems.  Can someone tell the problem from the backtrace
below?  The stream was obtained with

  (sb-ext:process-input
    (sb-ext:run-program *dx-pathname* :input :stream :output nil :wait nil))

Thanks for any help,

Nicolas.

---------------------------------------------------------------------------
debugger invoked on a SIMPLE-ERROR in thread 8108: SIGPIPE at #X90003848

You can type HELP for debugger help, or (SB-EXT:QUIT) to exit from SBCL.

restarts (invokable by number or by possibly-abbreviated name):
  0: [ABORT   ] Reduce debugger level (leaving debugger, returning to toplevel).
  1: [TOPLEVEL] Restart at toplevel READ/EVAL/PRINT loop.
(SB-UNIX::SIGPIPE-HANDLER
 3
 #<unavailable argument>
 #<unavailable argument>
 #.(SB-SYS:INT-SAP #XBFFFF4A0))[:EXTERNAL]
0] back

0: (SB-UNIX::SIGPIPE-HANDLER
    3
    #<unavailable argument>
    #<unavailable argument>
    #.(SB-SYS:INT-SAP #XBFFFF4A0))[:EXTERNAL]
1: ("foreign function call land:")
2: (SB-UNIX:UNIX-WRITE 4 13 #.(SB-SYS:INT-SAP #X0086B000) 0 547)[:EXTERNAL]
3: (SB-IMPL::FROB-OUTPUT
    5
    #<FILE-STREAM for "descriptor 13" {48001669}>
    #.(SB-SYS:INT-SAP #X0086B000)
    0
    547
    T)[:EXTERNAL]
4: (SB-IMPL::FLUSH-OUTPUT-BUFFER
    1
    #<FILE-STREAM for "descriptor 13" {48001669}>)[:EXTERNAL]
5: ("hairy arg processor for top level local call FORCE-OUTPUT"
    #<FILE-STREAM for "descriptor 13" {48001669}>)
6: ((GRAPHICS:GRAPHIC-OUTPUT (T T))
    #<unavailable argument>
    #<unavailable argument>
    #<<SKELETON> {484E3309}>
    :DX
    (:CELLS
     (#<MESH::<2-SIMPLEX> {4867C131}>{MP=#(0.16666666666666666d0
                                           0.16666666666666666d0)}
      #<MESH::<2-SIMPLEX> {4867C141}>{MP=#(0.6666666666666666d0
                                           0.16666666666666666d0)}
      #<MESH::<2-SIMPLEX> {4867C151}>{MP=#(0.33333333333333337d0
                                           0.3333333333333333d0)}
      #<MESH::<2-SIMPLEX> {4867C161}>{MP=#(0.16666666666666666d0
                                           0.6666666666666667d0)})
     :DIMENSION
     2))
7: ...