On 8/24/10 1:54 PM, Bartek Æwik³owski wrote:

Hello Michael,

This is because instance selection is solely based on instance heads, it doesn't consider contexts. There's a nice explanation available here: http://www.haskell.org/haskellwiki/GHC/AdvancedOverlap

The fix in this case is very easy because there are only two cases (and you don't want to provide new Nat class instances):

instance Show Z where show _ = "0"

instance Nat n => Show (S n) where show _ = show $ toInt (undefined :: n) + 1

regards, Bartek Æwik³owski OK, thanks!

Mike