[Haskell-cafe] Pointless functors
greenrd at greenrd.org
Thu Mar 12 22:30:47 EDT 2009
For most functors, that is equivalent to
point x = undefined
But by that logic, everything is a member of every typeclass...
On Fri, 13 Mar 2009 17:35:31 +0300
Eugene Kirpichov <ekirpichov at gmail.com> wrote:
> 'An arbitrary element' means 'undefined will suffice'
> point x = fmap (const x) undefined
> 2009/3/13 Ross Paterson <ross at soi.city.ac.uk>:
> > On Fri, Mar 13, 2009 at 03:18:15PM +0100, Martijn van Steenbergen
> > wrote:
> >> Are there any functors f for which no point/pure/return :: a -> f
> >> a exists?
> > No. Choose an arbitrary element shape :: f () and define
> > point x = fmap (const x) shape
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