module Control.Monad.Supply.Class where
import Prelude.Compat
import Control.Monad.Supply
import Control.Monad.State
import Control.Monad.Writer
class Monad m => MonadSupply m where
fresh :: m Integer
instance Monad m => MonadSupply (SupplyT m) where
fresh = SupplyT $ do
n <- get
put (n + 1)
return n
instance MonadSupply m => MonadSupply (StateT s m) where
fresh = lift fresh
instance (Monoid w, MonadSupply m) => MonadSupply (WriterT w m) where
fresh = lift fresh
freshName :: MonadSupply m => m String
freshName = fmap (('$' :) . show) fresh