You can use GADTs for this. For example: data Showable where Showable :: Show a ... | Hacker News

Hacker Newsnew | past | comments | ask | show | jobs | submit

		brentshields on March 30, 2014 \| parent \| context \| favorite \| on: Class Hierarchies? Don't Do That You can use GADTs for this. For example: `data Showable where Showable :: Show a => a -> Showable` This allows you to create a polymorphic container like [Showable 5, Showable "hello"] where the polymorphic type is constrained to be a member of the Show typeclass.

tel on March 30, 2014 [–]

Note that GADTs are a bit overkill for this. All you really need is ExistentialQuantification. GADTs are ExistentialQuantification + TypeEqualities.

Guidelines | FAQ | Lists | API | Security | Legal | Apply to YC | Contact