Haskell-brick toggling example

BrickToggler.hs

module Lib
    ( someFunc
    ) where

import Brick
import Brick (Widget, simpleMain, (<+>), str, withBorderStyle, joinBorders)
import Brick.Widgets.Center (center)
import Brick.Widgets.Border (borderWithLabel, vBorder)
import Brick.Widgets.Border.Style (unicode)

import Control.Monad (void, forever)
import Control.Monad.State.Strict

import qualified Graphics.Vty as V

-- This is an "empty" type.
-- We're not using any custom events in our app, so this will be the type we use for events.
data Void

-- The type of state used for this demonstration is Bool.
-- This draws a pane that is either filled with 'x' or '.', depending on whether the state is True or False.
drawPane :: Bool -> Widget ()
drawPane b = if b then fill 'x' else fill '.'

-- This is the main drawing function for our demo.
-- It draws two panes, side-by-side.
-- The state determines which of the two panes is filled by 'x's and which is filled by '.'s.
drawUI :: Bool -> [Widget ()]
drawUI b = [drawPane b <+> drawPane (not b)]

-- The event handler for our app.
-- When the escape key is pressed, the application halts.
-- When any other key is pressed, the state is toggled.
appEvent :: BrickEvent () Void -> EventM () Bool ()
appEvent e =
    case e of
        VtyEvent (V.EvKey V.KEsc []) -> halt        -- halt when Esc is pressed
        VtyEvent _ -> state (\b -> ((), not b))     -- toggle the state when anything else is pressed

toggleApp :: App Bool Void ()
toggleApp =
    App {
        appDraw = drawUI,
        appChooseCursor = showFirstCursor,
        appHandleEvent = appEvent,
        appStartEvent = return (),
        appAttrMap = const $ attrMap V.defAttr []
    }
    
main :: IO ()
main = void $ customMainWithDefaultVty Nothing toggleApp True