FrontEnd.hs

-- |
-- Module: WildBind.FrontEnd
-- Description: Data types and type classes about front-ends.
-- Maintainer: Toshio Ito <debug.ito@gmail.com>
--
-- Data types and type classes about front-ends.
-- 
-- You have to look at this module if you want to create a front-end
-- implementation.
module WildBind.FrontEnd
       ( FrontEvent(..),
         FrontEnd(..)
       ) where

import WildBind.Description (ActionDescription)

-- | Event from the front-end. @s@ is the state of the front-end. @i@ is the input.
data FrontEvent s i = FEInput i -- ^ An event that a new input is made.
                    | FEChange s  -- ^ An event that the front-end state is changed.
                    deriving (Show)

-- | Interface to the front-end. @s@ is the state of the front-end,
-- @i@ is the input.
data FrontEnd s i =
  FrontEnd
  { frontDefaultDescription :: i -> ActionDescription,
    -- ^ Default 'ActionDescription' for inputs
    frontSetGrab :: i -> IO (),
    -- ^ Action to grab (or capture) the specified input symbol on the device. 
    frontUnsetGrab :: i -> IO (),
    -- ^ Action to release the grab for the input symbol.
    frontNextEvent :: IO (FrontEvent s i)
    -- ^ Action to retrieve the next event. It should block if no event is queued.
  }