The difference the ~ makes in this case is that `uncurry4 (\_ _ _ _ -> ()) undefined` evaluates to `()` instead of bottom. The ~ is called an irrefutable pattern, and it helps make code that pattern matches on constructors more lazy. This seems like a good explanation of the subject:
http://en.wikibooks.org/wiki/Haskell/Laziness#Lazy_pattern_matching
On Mon, Feb 18, 2013 at 2:02 PM,
<briand@aracnet.com> wrote:
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
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