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{-# LANGUAGE DerivingVia #-}
module SC.Monad where
import Control.Monad.Trans.Class (lift)
import Control.Monad.Trans.Except
import Control.Monad.Trans.State.Strict
newtype SC a = SC (ExceptT String (State Int) a)
deriving (Functor, Applicative, Monad) via (ExceptT String (State Int))
instance MonadFail SC where
fail = throw
evalSC :: SC a -> Either String a
evalSC (SC m) = evalState (runExceptT m) 1
genId :: SC Int
genId = SC $ do
value <- lift get
lift (modify (+1))
return value
throw :: String -> SC a
throw = SC . throwE
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