[gambit-list] How use (read-char) to read individual characters from the console?

Marc Feeley feeley at iro.umontreal.ca
Thu Jan 3 10:24:38 EST 2013

On 2013-01-02, at 6:05 PM, Mikael <mikael.rcv at gmail.com> wrote:

> Here's a read-char suitable for console games etc. .
> (define (nice-read-char)
>    (tty-mode-set! (repl-input-port) #t #f #t #f 0)
>    (let ((c (read-char)))
>       (tty-mode-set! (repl-input-port) #t #t #f #f 0)
>       (if (eq? c #\x) (raise "Escape to REPL")) ; CTRL-C replacement
>       c))
> A version 2 of it would be to make it handle ctrl+c appropriately, currently that throws the console into a state as per the previous email.

A much simpler solution for your use case is to start gsi with the "-" option and put the current-input-port (stdin) in cooked mode, leaving the repl-input-port (the controlling terminal) alone:

% gsi -  
> (tty-mode-set! (current-input-port) #t #f #t #f 0)
> (list (read-char) (read-char)) ;; after this I will type the keys 1 and 2 without enter
(#\1 #\2)
> ,q

That way you won't have to flip the mode back and forth when reading a raw character.  Note that this works because with the "-" option, gsi will be in "batch mode" where it uses distinct ports for the current-input-port and the repl-input-port.  When gsi is in interactive mode (without the "-" option or file names), the same port is used (the controlling terminal):

% gsi -
> (repl-input-port)   
#<input-output-port #2 (console)>
> (current-input-port)
#<input-port #3 (stdin)>
> ,q

% gsi
Gambit v4.6.6

> (repl-input-port)
#<input-output-port #2 (console)>
> (current-input-port)
#<input-output-port #2 (console)>
> ,q
*** EOF again to exit

If your use case requires that the repl-input-port and current-input-port are the same, then you could use the following strategy which puts the tty in cooked mode only when the REPL reads a command:

(define (wrap-in-cooked-tty fn)
  (lambda args
    (let ((result (apply fn args)))

(define (cooked-tty)
  (tty-mode-set! (repl-input-port) #t #t #f #f 0))

(define (raw-tty)
  (tty-mode-set! (repl-input-port) #t #f #t #f 0))


(let ((channel (##thread-repl-channel-get! (current-thread))))
  (include "~~/lib/_gambit#.scm")
   (wrap-in-cooked-tty (macro-repl-channel-read-command channel))))


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