If you use a newtype the answer to the second question is yes. Just put
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
in the first line of your module or pass -XGeneralizedNewtypeDeriving to
ghc or ghci.
Daryoush Mehrtash schrieb:
What happens when a type adds driving such as:
newtype SupplyT s m a = SupplyT (StateT [s] m a)
deriving (Functor
<http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#t:Functor>,
Monad <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#t:Monad>,
MonadTrans, MonadIO)
Two questions:
How does the deriving implement the instance?
Is there a way for me to add my own classes in the deriving? for example
newtype .....
deriving( xyz)
Thanks
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