gistfile1.hs

import Control.Monad.Instances
import Control.Monad.Reader


data Env = Env Int Int


foo :: Int -> Env -> Int
foo a (Env x _) = a + x

bar :: Int -> Env -> Int
bar a (Env _ y) = a * y

-- >>> foo 4 >>= bar $ Env 1 10
-- 50


foo' :: Int -> Reader Env Int
foo' a = do Env x _ <- ask
            return $ a + x

bar' :: Int -> Reader Env Int
bar' a = do Env _ y <- ask
            return $ a * y

-- >>> runReader (foo' 4 >>= bar') $ Env 1 10
-- 50