[QuickCheck] Positive instance is broken

[Nick Smallbone]

Ah, bugger. What happens is that showHex has a base case when its
argument is 0, which desugars into a comparison with fromInteger 0 --
but since Positive's fromInteger doesn't allow you to construct
non-positive numbers, this case never matches.

I think I'll have to do what I was trying to avoid, and remove the Num
instance for Positive and friends entirely. It doesn't really make
sense to have a numeric type without 0 in it. This means that your
earlier bug report, about Small (Positive Int), will now fail to
typecheck, but Positive (Small Int) will do the right thing.

Nick

On Thursday 05 June, 2014 at 09:57 pm, Bryan O'Sullivan wrote:
> This goes into an infinite loop in ghci:
> 
> >>> import Numeric
> >>> import Test.QuickCheck
> >>> showHex (1 :: Positive Int) ""

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