[Haskell-cafe] instance (Enum a) => IArray UArray a

Twan van Laarhoven twanvl at gmail.com
Fri Jan 20 18:29:21 CET 2012

On 20/01/12 16:31, Mikhail Arefiev wrote:
 > Is there a reason why there is no instance of (Enum a) =>  IArray
 > UArray a (other than that it will require OverlappingInstances and/or
 > IncoherentInstances if e. g. UArray of Bools is used in the same
 > code)?
 > ...
 > Does having such thing make any sense?

The problem is that there are Enum instances for things for which 
to/fromEnum doesn't make sense, such as Double, Float and Integer.

    Prelude> fromEnum (12345678901234567890 :: Integer)

You wouldn't want your Integers to be stored as Ints in an array.


More information about the Haskell-Cafe mailing list