Subtle difference between standard instances
dons at galois.com
Tue Oct 28 13:18:15 EDT 2008
> We, at Anygma, noticed that a and b below have different behavior:
> a, b :: (Int->Int) -> (Int,Int) -> (Int,Int)
> a = fmap
> b = second
> See the blog post at http://netsuperbrain.com/blog/?p=74.
> The standard instances for Functor, Monad, and Applicative for tuples is
> strict. The Arrow on (->) when applied to tuples with first and second,
> however is non-strict.
> It is a subtle discrepancy, but it does make a difference for FRP when
> deriving these standard instances. Any objections to making the Functor,
> Monad, and Applicative instances for tuples non-strict like Arrows?
Changes to this kind of thing should be proposed on the libraries@
mailing list, via the submission process.
Since you guys are experts in FRP, I imagine this should be fine :)
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