Haskell/XMonad:围绕Monad的包装器,它还跟踪数据
这是一个后续行动。我要求对Haskell/XMonad:围绕Monad的包装器,它还跟踪数据,haskell,wrapper,monads,xmonad,Haskell,Wrapper,Monads,Xmonad,这是一个后续行动。我要求对X t操作“需要清理”(完成后松开按钮和/或键盘)的情况进行类型检查。他的回答是一个一元包装器NeedsCleanup,我当前的实现是这样的: {-# LANGUAGE GeneralizedNewtypeDeriving #-} newtype NeedsCleanup m t = NeedsCleanup { -- | Escape hatch from the NeedsCleanup Monad; -- returns
X t
操作“需要清理”(完成后松开按钮和/或键盘)的情况进行类型检查。他的回答是一个一元包装器NeedsCleanup
,我当前的实现是这样的:
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
newtype NeedsCleanup m t =
NeedsCleanup
{
-- | Escape hatch from the NeedsCleanup Monad;
-- returns the original action.
original_action :: m t
}
deriving (Functor, Applicative, Monad)
-- | executes unclean_action and cleans up afterwards.
-- (cleanedUp action) is a normal X() action
cleanedUp :: NeedsCleanup X t -> X t
cleanedUp unclean_action = do
result <- original_action unclean_action
doCleanup
return result
两个cleanUpdatea
可以组合在一起,大致形成一个联合(“之后,您必须对这两个操作进行清理”)
例如,如果:
action1::NeedsCleanup X()
与dta1::cleanupda
action2::NeedsCleanup X()
与dta2::cleanupda
然后,action1>>action2
应该与CombineCleanUpdatea dta1 dta2
相关联(大致为“您需要为两者清理的内容”)
最后,函数cleanedUp::NeedsCleanup X t->X t
应该执行底层的X t
操作,并获取该操作的cleanupda
(以查看需要清理的内容)
是否可以使用一元包装器以这种方式跟踪数据
更新:
最后,我使用了与Ilmo Euro的答案类似的东西,只是为CleanUpdatea定义了一个幺半群结构,而不是使用列表幺半群。类似于:
import Control.Monad.Writer.Lazy (WriterT(..), runWriterT, tell, MonadWriter(..))
import Control.Monad.Trans.Class (MonadTrans(..))
import Data.Monoid (Monoid(..))
initialCleanupData =
CleanupData
{
keyboard_needs_cleanup = False
, buttons_needing_cleanup = Set.empty
-- initial values for other fields
}
instance Monoid CleanupData where
mempty = initialCleanupData
mappend = combineCleanupData
newtype NeedsCleanup m t =
NeedsCleanup
{
to_writable :: WriterT CleanupData m t
} deriving (MonadTrans, Monad, Applicative, Functor, MonadIO, MonadWriter CleanupData)
cleanup :: NeedsCleanup X t -> X t
cleanup action = do
(ret_val, cleanup_data) <- runWriterT (to_writable action)
-- clean up based on cleanup_data
-- ...
return ret_val
needsCleanup_GrabButton
:: MonadIO m => Display -> Window -> Button -> NeedsCleanup m ()
needsCleanup_GrabButton dply window button = do
liftIO $ grabButton dply button anyModifier window True buttonReleaseMask grabModeAsync grabModeAsync none none
tell cleanup_data
where
-- the stuff we need to clean up from this
-- particular action
cleanup_data = initialCleanupData
{
buttons_needing_cleanup = Set.singleton button
}
例如,您可以使用
Writer
monad:
import Control.Monad.Writer
data DirtyThing = Keyboard | Mouse
newtype Dirty m a = Dirty { unDirty :: WriterT [DirtyThing] m a }
doFoo :: Dirty IO ()
doFoo = -- doing something dirty
cleanup :: Dirty m a -> m a
cleanup action = do
(val, dirtyThings) <- runWriterT (unDirty action)
-- cleanup dirtyThings
return val
import Control.Monad.Writer
数据脏东西=键盘|鼠标
newtype Dirty ma=Dirty{underty::WriterT[DirtyThing]ma}
doFoo::脏IO()
doFoo=--做一些肮脏的事情
清理::脏m a->m a
清理动作=do
(val,dirtyThings)我最终使用了类似的东西,只是为cleanUpdatea定义了一个幺半群结构(参见OP)。您能检查我是否正确定义了需要清理抓取按钮吗?(我想,但我不确定,这就是我应该如何使用tell
)@SPACINGISE它看起来不错,虽然有点不习惯。我会像liftIO$。。。;告诉你你的数据;return()
好的,我想我明白了,谢谢;必须使NeedsCleanup
成为MonadWriter cleanupda
的一个实例。如果我错了,请纠正我,但我不认为最后一个return()
是必要的?
needsCleanup_GrabButton
:: MonadIO m => Display -> Window -> Button -> NeedsCleanup m ()
needsCleanup_GrabButton dply window button = do
liftIO $ grabButton dply button anyModifier window True buttonReleaseMask grabModeAsync grabModeAsync none none
tell cleanup_data
where
-- the stuff we need to clean up from this
-- particular action
cleanup_data = initialCleanupData
{
buttons_needing_cleanup = Set.singleton button
}
import Control.Monad.Writer
data DirtyThing = Keyboard | Mouse
newtype Dirty m a = Dirty { unDirty :: WriterT [DirtyThing] m a }
doFoo :: Dirty IO ()
doFoo = -- doing something dirty
cleanup :: Dirty m a -> m a
cleanup action = do
(val, dirtyThings) <- runWriterT (unDirty action)
-- cleanup dirtyThings
return val