我正在使用新的背包模块系统和Cabal 2。我有以下签名:
{-# LANGUAGE KindSignatures #-}
signature Streamy where
import Control.Monad
import Control.Monad.Trans.Class
import Control.Monad.IO.Class
data Stream :: * -> (* -> *) -> * -> *
instance Monad m => Functor (Stream o m)
instance Monad m => Applicative (Stream o m)
instance Monad m => Monad (Stream o m)
instance MonadIO m => MonadIO (Stream o m)
instance MonadTrans (Stream o)
Stream
键入自
streaming
,如下所示:
import Streaming (Of(..))
import qualified Streaming as Q
type Stream o m r = Q.Stream (Of o) m r
然而,这给了我一个错误
抽象数据实现中的非法参数化类型同义词。
o
坐在
Of
Q.Stream
.
我可以通过定义适配器新类型来解决这个问题:
{-# language GeneralizedNewtypeDeriving #-}
newtype S o m r = S { unS :: Q.Stream (Of o) m r }
deriving (Functor,Applicative,Monad,MonadIO,MonadTrans)
type Stream = S
有没有其他不需要定义新类型的方法?
