Pointers

haskell.hs

class Monad m => Ref r m where
  ref :: a -> m (r a)
  (*) :: r a -> m a
  (*=) :: r a -> a -> m ()
  (*$) :: r a -> (a -> a) -> m ()
  r *$ f = (r *) >>= (*=) r . f

instance Ref IORef IO where
  ref = newIORef
  (*) = readIORef
  (*=) = writeIORef

instance Typeable t => Show (IORef t) where
  show _ = "IORef " ++ show (typeOf (undefined :: t))

f r v = r *= v

main = do
  y :: IORef Int <- ref 10
  print y
  print =<< (y *)
  f y 25
  print =<< (y *)
  y *$ (+ 35)
  print =<< (y *)

-- IORef Int
-- 10
-- 25
-- 60

scala.scala

class *[T](var value: T) {
  def *=(t: T) {
    value = t
  }

  def *() = value

  override def toString = "ref to " + value
}

object * {
  def &[T](x: T) = new *(x)
}

object RefTest {
  import *._

  def f(v:Int, x: *[Int]) {
    x*=v
  }

  def main(args: Array[String]) {
    val y = &(1)
    println(y*)
    println(y)
    f(3, y)
    println(y*)
    println(y)
  }
}

// 1
// ref to 1
// 3
// ref to 3