Stephan Friedrichs wrote:
Oh I see - my bad. I was somehow thinking I could prevent modification
of the input list but that's obviously impossible when the ConsumerT
constructor is... exported? public? how do you say that?
You can export ConsumerT as an abstract type constructor.
> {-# LANGUAGE GeneralizedNewtypeDeriving #-}
> module ConsumerT(ConsumerT, runConsumerT, next) where
> import Control.Monad.State
> import Control.Monad.Trans
> newtype ConsumerT c m a = ConsumerT { runConsumerT' :: StateT [c] m a }
> deriving (Functor, Monad, MonadTrans)
> runConsumerT = runStateT . runConsumerT'
> next :: Monad m => ConsumerT a m a
> next = ConsumerT $ StateT $ \(x:xs) -> return (x, xs)
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