plp/haskell/haskell3.hs

module Haskell3 where

import qualified Data.Map as M
import Control.Monad

-- define Monads yeahhhh

foo :: Maybe String
foo = do
        x <- Just 3
        y <- Just "!"
        Just (show x ++ y)

-- Carrier example with maps and monads double yeahhh

type PersonName = String
type PhoneNumber = String
type BillingAddress = String
data MobileCarrier = TIM | Vodadone | Wind deriving (Eq, Ord, Show)

findCarrierBillingAddress :: PersonName 
                         -> M.Map PersonName Phonenumber
                         -> M.Map PhoneNumber MobileCarrier
                         -> M.Map MobileCarrier BillingAddress 
                         -> Maybe BillingAddress
findCarrierBillingAddress person phoneMap carrierMap addressMap =
        case M.lookup person phoneMap of
          Nothing -> Nothing
          Just number ->
                  case M.lookup number carrierMap of
                    Nothing -> Nothing
                    Just carrier -> M.lookup carrier addresMap

 
findCarrierBillingAddress2 :: PersonName 
                         -> M.Map PersonName Phonenumber
                         -> M.Map PhoneNumber MobileCarrier
                         -> M.Map MobileCarrier BillingAddress 
                         -> Maybe BillingAddress
findCarrierBillingAddress2 person phoneMap carrierMap addressMap = do
        number <- M.lookup person phoneMap
        carrier <- M.lookup number carrierMap
        M.lookup carrier addressMap