[Haskell-cafe] Pointless functors
ross at soi.city.ac.uk
Fri Mar 13 12:28:01 EDT 2009
On Sat, Mar 14, 2009 at 02:12:45AM +1000, Matthew Brecknell wrote:
> Ross Paterson wrote:
> > No. Choose an arbitrary element shape :: f () and define
> > point x = fmap (const x) shape
> Interesting. Is the arbitrariness of the shape some sort of evidence
> that Pointed is not really a very useful class in its own right?
Not useless, but equivalent to
class Functor f => Pointed f where
unit :: f ()
Naturality of point does the rest. But not all definitions of unit
are equally useful.
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