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)
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