On 18/02/13 19:02, 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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[1] explains it in section 4.4 — ‘Lazy patterns’. [1] - http://www.haskell.org/tutorial/patterns.html -- Mateusz K.

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, 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

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe