[Haskell-cafe] Equality Contstraint?
rasen.dubi at gmail.com
Fri May 15 01:26:23 UTC 2015
It's irrefutable pattern - the pattern that matches lazily. You can get
more info here .
Hope this helps,
On Fri, May 15, 2015 at 4:17 AM Michael Jones <mike at proclivis.com> wrote:
> I am poking around in Arrow to understand it better. There is the
> following definition:
> second :: a b c -> a (d,b) (d,c)
> second f = arr swap >>> first f >>> arr swap
> swap :: (x,y) -> (y,x)
> swap ~(x,y) = (y,x)
> Can someone explain what the ~ is? Searching the net resulted in
> I kind of think it is some kind of equality constraint but can’t find
> documentation. Perhaps if I knew what it was called I might succeed in
> finding something. If it is an equality constraint, please provide a
> reference if you have one. I did not find anything in a search including
> GHC, etc.
> Haskell-Cafe mailing list
> Haskell-Cafe at haskell.org
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