Hi all, On Wednesday 25 November 2009 22:46:42 Luke Palmer wrote:
I feel like this should be qualified. Type classes are not for name punning ; you wouldn't use a type class for the method bark on types Tree and Dog. But if you have a well-defined *structure* that many types follow, then a type class is how you capture that. It sounds like you do have this structure in your example.
Further, with typeclasses, you can write methods that are generic over any type with that structure. So:
class Temporal a where time :: a -> Time
temporalOrder :: Temporal a => [a] -> [a] temporalOrder = sortBy (comparing time)
The ability to do this indicates why using them for punning is a bad idea.
While I agree that this utility of typeclasses is lost if they are used for name punning, I'm still unconvinced that it is actively *harmful* to use classes for this lesser purpose :) I think punning is a worthwhile goal on its own, since I find myself wasting quite some thought on whether to prefix a record field name somehow, and if I do, what I should use as a short but sufficiently unique prefix. Greetings, Daniel