Hi
I have most of a Data.Nat library done, I should finish it off and release it...
Thanks
Neil
On 6/22/07, Stefan O'Rear
On Fri, Jun 22, 2007 at 07:14:39PM +0100, Andrew Coppin wrote:
Chaddaï Fouché wrote:
You should be using BS.null f rather than BS.length f > 0.
While we're on the subject... anybody know a neat way to check, say, whether a list contains exactly 1 element? (Obviously pattern matching can do it, but that requires big case-expressions...)
data LazyNat = Zero | Succ LazyNat deriving(Eq,Ord)
instance Enum LazyNat where succ = Succ pred (Succ x) = x
toEnum 0 = Zero toEnum (x+1) = succ (toEnum x)
fromEnum Zero = 0 fromEnum (Succ x) = fromEnum x + 1
instance Num LazyNat where -- this is a lie, the lifted naturals only -- form a *semi*ring. Sigh. fromIntegral = toEnum
Zero + y = y Succ x + y = Succ (x + y)
Zero * y = 0 Succ x * y = y + x * y
abs = id signum 0 = 0 signum _ = 1
x - Zero = x Succ x - Succ y = x - y
length' [] = Zero length' (x:xs) = Succ (length xs)
null x = length' x == 0
one x = length' x == 1
atLeastFive x = length' x >= 5
Stefan _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe