Am Montag, 16. Februar 2009 14:21 schrieben Sie: > Aha! Wolfgang is a man who knows his own code :) > Yes, I've seen this a couple of times but when I saw it again in > Grapefruit, I wanted to know how this usage of existentials worked, since > I'm sooo curious to find out how you managed to use the type system for > solving some of the typical FRP problems.
Note that in Grapefruit I not only use rank-2 polymorphism (corresponding to existentials) but also impredicative polymorphism, namely in FRP.Grapefruit.Signal.switch. However, the idea behind using impredicativity here is the same as the reason for using rank-2 in Control.Monad.ST.runST, FRP.Grapefruit.Circuit.create and Graphics.UI.Grapefruit.Circuit.run. Best wishes, Wolfgang _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe