2 Aug
2007
2 Aug
'07
8:49 p.m.
On Fri, Aug 03, 2007 at 01:45:03AM +0100, Neil Mitchell wrote:
Hi
Catch (www.cs.york.ac.uk/~ndm/catch) can infer that certain uses of numbers fit into the {Neg, Zero, One, Pos} abstraction - so for example it can infer that length returns {Zero, One, Pos}, but not Neg. If you then do:
xs !! length ys
It will detect that length ys is natural, and will be safe. However, if you pass any arbitrary value as the index to !! it will warn of a possible pattern match error.
I hope catch doesn't actually think that's safe, because it's not - set ys = xs = [1,2,3,4,5], you'll get an index out of range error. (Yes, I deliberately chose a list longer than 4 elements). Stefan