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hack the port-column of current-output-port after printing a prompt

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* module/ice-9/boot-9.scm (repl-reader): Reset the output-column to 0
  after printing the prompt.  Fixes bug 9664.
This commit is contained in:
Andy Wingo 2011-11-16 23:13:55 +01:00
parent 440ac793c4
commit dceb78294d
1 changed files with 20 additions and 1 deletions
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21
module/ice-9/boot-9.scm
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@ -2923,7 +2923,26 @@ module '(ice-9 q) '(make-q q-length))}."
(define repl-reader
(lambda* (prompt #:optional (reader (fluid-ref current-reader)))
(if (not (char-ready?))
(display (if (string? prompt) prompt (prompt))))
(begin
(display (if (string? prompt) prompt (prompt)))
;; An interesting situation. The printer resets the column to
;; 0 by printing a newline, but we then advance it by printing
;; the prompt. However the port-column of the output port
;; does not typically correspond with the actual column on the
;; screen, because the input is is echoed back! Since the
;; input is line-buffered and thus ends with a newline, the
;; output will really start on column zero. So, here we zero
;; it out. See bug 9664.
;;
;; Note that for similar reasons, the output-line will not
;; reflect the actual line on the screen. But given the
;; possibility of multiline input, the fix is not as
;; straightforward, so we don't bother.
;;
;; Also note that the readline implementation papers over
;; these concerns, because it's readline itself printing the
;; prompt, and not Guile.
(set-port-column! (current-output-port) 0)))
(force-output)
(run-hook before-read-hook)
((or reader read) (current-input-port))))