[Haskell-cafe] Re: [Haskell] How to define tail function for
Even/Odd GADT lists?
iavor.diatchki at gmail.com
Wed Apr 23 19:55:51 EDT 2008
I am not sure of the use case here but you could also do the following:
data EvenList a = Nil
| ConsE a (OddList a)
data OddList a = ConsO a (EvenList a)
This does not use any type system extensions.
On Wed, Apr 23, 2008 at 4:46 PM, David Roundy <daveroundy at gmail.com> wrote:
> 2008/4/23 Martijn Schrage <martijn at cs.uu.nl>:
> > 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. :)
> Haskell-Cafe mailing list
> Haskell-Cafe at haskell.org
More information about the Haskell-Cafe