[Haskell-cafe] Instances for Set of Functor, Traversable?
lemming at henning-thielemann.de
Mon Jul 26 18:05:02 EDT 2010
On Mon, 26 Jul 2010, Gregory Crosswhite wrote:
> Is there a specific reason why Set doesn't have instances for Functor
> and Traversable?
Sure, fmap needs an Ord restriction for the element type, which is not
possible for the plain Functor constructor class. E.g. in
fmap (const 'a') set
all result elements will coincide. If you need such an fmap, try
More information about the Haskell-Cafe