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Read characters from without newline

From: Zelphir Kaltstahl
Subject: Read characters from without newline
Date: Sat, 28 Aug 2021 14:09:52 +0000

Hello Guile users,

I am trying to find a way to read a character from command line or REPL, without
having to enter a newline, confirming the input.

For example I found this for Python:

I read on
<> about
buffering and thought, that I could simply set the port to be unbuffered using
(setvbuf port 'none) and then call (get-char port) as follows:

 (except (rnrs base) let-values map)
 (only (guile)
       ;; lambda forms
       lambda* λ
       ;; input output
 (ice-9 textual-ports)
 (ice-9 optargs))

(let ([port (current-input-port)])
  (setvbuf port 'none)
  (get-char port))

However, this does not work. The terminal emulator might not send input
immediately to the Guile program. Even in the Guile REPL and in Emacs Geiser
this does not work. I guess it would work, if they did send each character
immediately to the Guile program, because the following works:

  (call-with-input-string "ab"
    (λ (in-port)
      (setvbuf in-port 'none)
      (get-char in-port))))

There is no newline in the string "ab" and only the "a" is displayed.

So the question might be, how one can get into a mode, where Guile receives
input immediately, taking over control of the terminal or REPL.

However, I am not sure how the Python solution does this.

I have some command line program, in which I let the user choose what to do next
by entering a character and then pressing the return key to confirm the input. I
think it would be nice to not have to press return all the time and only needing
to press the character's key.

Does anyone know how to do this in Guile?

Best regards,


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