Re: A Pointless Library Proposal

Ashley Yakeley wrote:

data MyGADT a where MyInt :: MyGADT Int MyChar :: MyGADT Char

never :: MyGADT Bool -> a

Annoyingly, this doesn't compile without adding a definition line mentioning a bottom value.

This can't be fixed because the desugaring is ambiguous. never might be _|_ or \x. _|_ or \x y. _|_ or ... How about never :: MyGADT Bool -> a never x = case x of {} which is just the desugared form of your intended empty definition? GHC doesn't allow it, but it would be a simple extension. -- Ben