Clarify relationship between Functor and Applicative
ekmett at gmail.com
Sat Feb 26 01:15:37 CET 2011
On Fri, Feb 25, 2011 at 5:42 PM, Ross Paterson <ross at soi.city.ac.uk> wrote:
> On Fri, Feb 25, 2011 at 05:34:18PM -0500, roconnor at theorem.ca wrote:
> > In the applicative documentation, it says for an Applicative functor f:
> > The Functor instance should satisfy
> > fmap f x = pure f <*> x
> > I think the documentation should be clarified that this does not
> > need to be checked because it is a consequence of the other
> > applicative laws.
> > See <http://hpaste.org/44315/applicative_implies_functor>.
> Do you have a proof that Functor instances are uniquely determined?
Given fmap id = id, the uniqueness of fmap for a given type follows
trivially from the free theorem.
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