Add flipped fmap
jonathanccast at fastmail.fm
Thu Apr 8 13:10:45 EDT 2010
On Thu, 2010-04-08 at 14:04 -0300, Felipe Lessa wrote:
> On Thu, Apr 8, 2010 at 9:45 AM, Bas van Dijk <v.dijk.bas at gmail.com> wrote:
> > I must say that Brent Yorheys comment about (<**>) not being flip
> > (<*>) has made the 'symmetry' argument less convincing and has moved
> > me a bit closer to the - camp. However, I'm still for adding it
> > because it can make code nicer.
> They -- <**> and <$$> -- are symmetric in spirit.
The equational law relating <$> to <*> for Applicative instances is
f <$> a = return f <*> a
We analogously have
a <$$> f = a <**> return f
as well. So the analogy between <$$> and <**> holds.
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