Grokking Reader Monad without implementation

reader_monad_sample.hs

import Control.Monad.Reader

-- ========================================= --
-- a base case (just for comparison)
-- ========================================= --

doJob1 :: ()     -> String
doJob2 :: String -> Int 
doJob3 :: Int    -> [String]
doJob1 = undefined
doJob2 = undefined
doJob3 = undefined

doJob12  =          doJob2 . doJob1
doJob123 = doJob3 . doJob2 . doJob1

-- > :t doJob12
-- doJob12 :: () -> Int
-- > :t doJob123
-- doJob123 :: () -> [String]

-- ========================================= --
-- Use a configuration
-- ========================================= --
data Conf = Conf [(Char, Int)]

doJob1' :: Conf -> ()     -> String
doJob2' :: Conf -> String -> Int 
doJob3' :: Conf -> Int    -> [String]
doJob1' = undefined
doJob2' = undefined
doJob3' = undefined

-- doJob12'  = ??
-- doJob123' = ??

doJob12'  = \x ->             doJob2' x $ doJob1' x ()
doJob123' = \x -> doJob3' x $ doJob2' x $ doJob1' x ()

-- > :t doJob12'
-- doJob12' :: Conf -> Int
-- > :t doJob123'
-- doJob123' :: Conf -> [String]

-- ========================================= --
-- Make use of Reader Monad
-- ========================================= --

doJobR1 :: ()     -> Reader Conf String 
doJobR2 :: String -> Reader Conf Int 
doJobR3 :: Int    -> Reader Conf [String]
doJobR1 = undefined
doJobR2 = undefined
doJobR3 = undefined

doJobR12  = doJobR1 () >>= doJobR2
doJobR123 = doJobR1 () >>= doJobR2 >>= doJobR3

-- > :t doJobR12
-- doJobR12 :: ReaderT Conf Data.Functor.Identity.Identity Int
-- > :t runReader doJobR12
-- runReader doJobR12 :: Conf -> Int

-- > :t doJobR123
-- doJobR123 :: ReaderT Conf Data.Functor.Identity.Identity [String]
-- > :t runReader doJobR123
-- runReader doJobR123 :: Conf -> [String]