On Tuesday 01 February 2011 20:14:05, Patrick LeBoutillier wrote:
Hi,
I've created an instance of Enum that repeats the same elements when it gets to the end:
Does this violate any implicit rules that an Enum instance should follow?
If you make that type also an instance of Bounded. Says the report:
For any type that is an instance of class Bounded as well as Enum, the following should hold:
* The calls succ maxBound and pred minBound should result in a runtime error. * fromEnum and toEnum should give a runtime error if the result value is not representable in the result type. For example, toEnum 7 :: Bool is an error. * enumFrom and enumFromThen should be defined with an implicit bound, thus: enumFrom x = enumFromTo x maxBound enumFromThen x y = enumFromThenTo x y bound where bound | fromEnum y >= fromEnum x = maxBound
| otherwise = minBound
but otherwise, it's okay.
Is there a better way to do this?
None obvious. Cheers, Daniel