Add annotation to specify operators precedence.

Is it possible to add some kind of annotation to control the precedence of functions with symbolic names, something similar to what Haskell has? 

``` scala
implicit class ArrowAssoc[A](left: A) {
  @infixr(6) def ->[B](right: B): (A, B) = (left, right)
}
```

So the code like this: `"string" -> "value" -> 10`, would be parsed as `("string" -> ("value" -> 10))`. 
