typeclasses and syntax in scala. monad example. this is approximately how scalaz works

typeclasses.scala

trait Monad[M[_]] {
  def apply[A](a: => A): M[A]
  def flatMap[A,B](value: M[A], f: A => M[B]): M[B]
  def map[A,B](value: M[A], f: A=>B): M[B] = flatMap(value, (v: A) => apply(f(v)))
}

object Monad {
  def apply[A[_]](implicit f: Monad[A]) = f
}

object MonadSyntax {
  implicit class MonadOps[A, M[_]: Monad](v: M[A]){
    def map[B](f: A=>B) = Monad[M].map(v,f)
    def flatMap[B](f: A=>M[B]) = Monad[M].flatMap(v,f)
  }
}

//...

final case class Id[A](a: A)

//...

implicit object IdFM extends Monad[Id] {
  def apply[A](a: => A) = Id(a)
  def flatMap[A,B](value: Id[A], f: A => Id[B]): Id[B] = f(value.a)
}

//...

import MonadSyntax._
Id("foo").flatMap(s => Id(s.length))

for {
  a <- Id(1)
  b <- Id(2)
} yield a + b