Polymorphism in Haskell

README.md

EasternOrder.hs

module EasternOrder where

	import Serializable
	import Person

	instance IsSerializable Person where
		serialize (Person f l) = l ++ " " ++ f

	easternOrder :: Person -> Serializable
	easternOrder = Serializable

EuropeanOrder.hs

module EuropeanOrder where

	import Serializable
	import Person

	instance IsSerializable Person where
		serialize (Person f l) = f ++ " " ++ l

	europeanOrder :: Person -> Serializable
	europeanOrder = Serializable

Main.hs

import Person
import Serializable
import EuropeanOrder
import EasternOrder

us = europeanOrder (Person "Barack" "Obama")
cn = easternOrder  (Person "Jintao" "Hu")

main = (print . serializeAll) [us, cn]

Obama.hs

import Person
import Serializable
import EuropeanOrder

main = (print . serialize) (Person "Barack" "Obama")

Person.hs

module Person where

	data Person = Person String String

Presidents.hs

import Person
import Serializable
import EuropeanOrder
import EasternOrder

us = europeanOrder (Person "Barack" "Obama")
cn = easternOrder  (Person "Jintao" "Hu")

main = (print . serializeAll) [us, cn]

Serializable.hs

module Serializable where

	import Data.List

	class IsSerializable a where
	    serialize:: a -> String

	data Serializable where
	    Serializable :: IsSerializable a => a -> Serializable

	serializeAll:: [Serializable] -> String
	serializeAll as = intercalate ", " (map (\(Serializable a) -> serialize a) as)