[Haskell-cafe] Re: [Haskell] How to define tail function for Even/Odd GADT lists?

2008/4/23 Martijn Schrage :

It depends a bit on what you want to use these lists for, but the following encoding works for your examples and doesn't need the type class.

data E data O

type Even = (E,O) type Odd = (O,E)

That's a nice little trick! I like how you achieve type signatures relating two distinct types just by sticking them in a tuple. :) David