map and fmap

Bulat Ziganshin bulat.ziganshin at
Tue Aug 15 02:19:28 EDT 2006

Hello Duncan,

Tuesday, August 15, 2006, 2:37:50 AM, you wrote:

> If it goes in that direction it'd be nice to consider the issue of
> structures which cannot support a polymorphic map. Of course such
> specialised containers (eg unboxed arrays or strings) are not functors
> but they are still useful containers with a sensible notion of map.

unboxed arrays - not if you using implementation from ArrayRef lib

ByteStrings - can be also parameterized by its type elements, as i
always suggested. of course, these elements should be unboxable and
belong to the Storable class in order to allow peek/poke them

there is also faking solution:

type ByteStr a = ByteString
instance Functor ByteStr

(although i never tested it)

Best regards,
 Bulat                            mailto:Bulat.Ziganshin at

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