[wxhaskell-users] modify text control on input

[nat m. <taz...@gm...>]

I'm trying to make a text control that allows only letters and spaces, and
changes letters to underscores* as you type*. So if you typed "abc123 def",
you would see "___ ___" appearing.

I thought the solution would be
controlOnText<http://hackage.haskell.org/packages/archive/wxcore/0.10.1/doc/html/Graphics-UI-WXCore-Events.html#v%3AcontrolOnText>,
which is nice because it works with both keyboard input and pasting. The
problem is it also gets called when I change the text using set. For example
here's a simple program that just reads the text and sets it again:

module Main where
import Graphics.UI.WX
import Graphics.UI.WXCore

main = start $
    do f <- frame []
       input <- textEntry f []
       controlOnText input $ update input
    where
        update input =
            do txt <- get input text
               set input [text := txt]

This doesn't work because it results in an infinite loop. In wxPython I can
use ChangeValue instead of SetValue to change the text without creating an
event, but I can't find anything like that in wxHaskell. Is there another
way to do this?