On Mon, Jun 25, 2007 at 07:31:09PM +0100, Ian Lynagh wrote:
I don't know if (^) in particular is what is causing you problems, but IMO it has the wrong type; just as we have (!!) :: [a] -> Int -> a genericIndex :: (Integral b) => [a] -> b -> a we should also have (^) :: (Num a) => a -> Int -> a genericPower :: (Num a, Integral b) => a -> b -> a
On Jun 25, 2007, at 11:40 AM, David Roundy wrote:
That would be great!
Ahh, a consensus I can enthusiastically support. It would seem to me a good library design rule of thumb to make ANY argument that will be counted down to zero by simple recursion an Int, with the type of (^) a standard application of this general principle. Even with strict evaluation and tail recursion, if I want to write something that's going to need more than 2^31 iterations, I want the compiler to make me jump through hoops to say so. With the current type for (^), I'm jumping through hoops to say something that I can more easily unroll by hand. Your proposal for (^) would allow genericPower to use the asymptotically faster algorithm of writing out the exponent in binary and multiplying together repeated squares, leaving the simple recursion to (^).