[Haskell-cafe] ~ operator ?

Hi all, I was creating "bigger" uncurries which I am simply extending from an existing uncurry I found some where, e.g. uncurry4 :: (a -> b -> c -> d -> e) -> ((a, b, c, d) -> e) uncurry4 f ~(a,b,c,d) = f a b c d when I realized, what's the "~" for ? I've only been able to find a partial explanation that it involves preserving laziness, or something, maybe ? I was hoping someone could enlighten me. Thanks Brian