import EnableGUI -- from http://wxhaskell.sourceforge.net/download/EnableGUI.hs

import Graphics.UI.WXCore
import Graphics.UI.WX hiding
import Data.Bits ((.&.), complement)

textCtrlSetSingleLine ctrl = do
  style <- windowGetWindowStyleFlag ctrl
  windowSetWindowStyleFlag ctrl (style .&. (complement wxTE_MULTILINE))

gui
  = do f <- frame [text := "single line textbox sample"]
       input <- textCtrlRich f [bgcolor := black, textColor := white, font := fontFixed{ _fontSize = 12 }]
       set f [layout := column 1 [hfill (widget input)]]
       set input [processEnter := True]
       textCtrlSetSingleLine input
       set input [on command := onEnter input]
       return ()
  where
      onEnter input
        = do
          txt <- get input text
          putStrLn txt
          set input [text := ""]

main = enableGUI >> start gui

import EnableGUI -- from http://wxhaskell.sourceforge.net/download/EnableGUI.hs

import Graphics.UI.WXCore hiding (Var)
import Graphics.UI.WX hiding (Var, enter)
import Data.Bits ((.&.), complement)

textCtrlSetSingleLine ctrl = do
  style <- windowGetWindowStyleFlag ctrl
  windowSetWindowStyleFlag ctrl (style .&. (complement wxTE_MULTILINE))

gui
  = do f <- frame [text := "single line textbox sample"]
       input <- textCtrlRich f [bgcolor := black, textColor := white, font := fontFixed{ _fontSize = 12 }]
       set f [layout := column 1 [hfill (widget input)]]
       set input [processEnter := True]
       textCtrlSetSingleLine input
       set input [on command := onEnter input]
       return ()
  where
      onEnter input
        = do
          txt <- get input text
          putStrLn txt
          set input [text := ""]

main = enableGUI >> start gui

This snippet shows you how to create a single-line text box, or how to use windowGetWindowStyleFlag.
Press enter to put text in the textbox into the console.

Single line textbox in wxHaskell

Haskell