On Thu, 22 Jul 2010, Chad Scherrer wrote:
Hello cafe,
I'm trying to do some things with bounded indices so I can carry around arrays (well, Vectors, really) without needing to refer to the bounds.
For example, if I know my indices are Bool values, I can do
rangeSize (minBound, maxBound :: Bool) 2
I'd like to be able to do this in general, but...
:t rangeSize (minBound, maxBound) <interactive>:1:11: Ambiguous type variable `a' in the constraints: `Bounded a' arising from a use of `minBound' at <interactive>:1:11-18 `Ix a' arising from a use of `rangeSize' at <interactive>:1:0-29 Probable fix: add a type signature that fixes these type variable(s)
I thought it might help to put it into a module and do a better job with the type, like this:
bdRangeSize :: (Ix i, Bounded i) => i -> Int bdRangeSize _ = rangeSize (minBound, maxBound :: i)
bdRangeSize x = rangeSize (minBound, maxBound `asTypeOf` x)