Paul Chiusano schrieb:
> def integerDivide[K](denominator: Int, vs: Map[K,Int]): Map[K,Int] =
> vs.transform((k,v) => v/denominator)
The type you specified is
exists K . (Int, Map[K, Int]) => Map[K, Int]
but the type you are after is
forall K . (Int, Map[K, Int]) => Map[K, Int]
That is universal, not existential. And universal types are the prototypical
hypothetical improvement to scala
(see
http://lampsvn.epfl.ch/svn-repos/scala/sip/trunk/sips/sip-00000.xhtml).
This may be related, too:
http://existentialtype.net/2008/05/26/revisiting-higher-rank-impredicative-polymorphism-in-scala/but it looks too scary for me right now.
IIRC i've read somewhere else that you can get the effect you want by
CPS-transforming your program, but I am not sure that this would be an
improvement in the scariness department.
- Florian
