On Thu, Mar 21, 2013 at 11:32:21AM +0100, matteo vezzola wrote:
I'm playing with tagless final interpreters reading [1], using a very simple language:
class Ints repr where int :: Integer -> repr Integer (.+.) :: repr Integer -> repr Integer -> repr Integer (.*.) :: repr Integer -> repr Integer -> repr Integer (.-.) :: repr Integer -> repr Integer (.<=.) :: repr Integer -> repr Integer -> repr Bool
newtype P repr t = P { unP :: Bool -> repr t } instance Ints repr => Ints (P repr) where int n = P $ \ s -> if s then int n else (.-.) (int n) (.-.) n = P $ unP n . not n .+. m = P $ \ s -> unP n s .+. unP m s
n .*. m = P $ \ s -> unP n s .*. unP m s n .<=. m = P $ \ s -> unP n s .<=. unP m s
Incidentally, these last two lines seem wrong. It is not the case that -(n*m) = (-n)*(-m) or that n <= m iff (-n) <= (-m). -Brent