George Leontiev folone

#Monoid in Scala by programmers from different backgrounds#

	import scalaz._, Scalaz._

	case class Writer[W: Monoid, +A](run: (A, W)) {
	def map[B](f: A ⇒ B): Writer[W, B] =
	Writer {
	val (a, w) = run
	(f(a), w)
	}

	def flatMap[B](f: A ⇒ Writer[W, B]): Writer[W, B] =

	case class Reader[T, +A](run: T ⇒ A) {
	def map[B](f: A ⇒ B): Reader[T, B] =
	Reader((r: T) ⇒ f(run(r)))

	def flatMap[B](f: A ⇒ Reader[T, B]): Reader[T, B] =
	Reader((r: T) ⇒ f(run(r)).run(r))

	def &&&[B](x: Reader[T, B]): Reader[T, (A, B)] =
	for {
	a ← this

	import Control.Applicative

	data NewYear = NewYear Int
	deriving (Eq, Show)
	data Happy a = Happy a
	deriving (Eq, Show)

	instance Functor Happy where
	fmap f (Happy a) = Happy $ f a

	import scalaz._, Scalaz._

	case class Happy[A](a: A)
	case class NewYear(year: Int)

	implicit val happyInstance = new Applicative[Happy] {
	def point[A](a: ⇒ A) = Happy(a)
	def ap[A, B](fa: ⇒ Happy[A])(f: ⇒ Happy[A => B]) =
	f match {
	case Happy(f) ⇒ fa match {

	% ghci
	GHCi, version 7.6.1: http://www.haskell.org/ghc/ :? for help
	Loading package ghc-prim ... linking ... done.
	Loading package integer-gmp ... linking ... done.
	Loading package base ... linking ... done.
	Prelude> let n = map show [1..10]
	Prelude> let c = \x y -> concat ["(", x, "+", y, ")"]
	Prelude> foldl c "0" n
	"((((((((((0+1)+2)+3)+4)+5)+6)+7)+8)+9)+10)"
	Prelude> foldr c "0" n

	shapeless [0849b6f...] % sbt
	[info] Loading project definition from /home/folone/workspace/shapeless/project
	[info] Set current project to shapeless (in build file:/home/folone/workspace/shapeless/)
	> shapeless-core/console
	[warn] Credentials file /home/folone/.ivy2/.credentials does not exist
	[info] Compiling 2 Scala sources to /home/folone/workspace/shapeless/core/target/scala-2.11/classes...
	[info] Compiling 24 Scala sources to /home/folone/workspace/shapeless/core/target/scala-2.11/classes...
	[info] Starting scala interpreter...
	[info]
	Welcome to Scala version 2.11.0-20130205-141957-132e09fc2e (OpenJDK 64-Bit Server VM, Java 1.7.0_09).

	type State[E] = Adjunction[({type λ[α] = Writer[E, α]})#λ, ({type λ[α] = Reader[E, α]})#λ]
	type Store[E] = Adjunction[({type λ[α] = Reader[E, α]})#λ, ({type λ[α] = Writer[E, α]})#λ]
	type Cont = Adjunction[Function0, Function0] // Function0 -\| Function0