Data instance for ratio changed, now incompatible

Using the following code:

import Data.Generics -- import Data.Data on 6.10
import Data.Ratio

-- data  (Integral a)      => Ratio a = !a :% !a  deriving (Eq)

u = undefined :: Ratio Integer

ctr t = head $ dataTypeConstrs $ dataTypeOf t

ctr2 t = length $ gmapQ (const undefined) $ asTypeOf (fromConstr $ ctr t) t

test = ctr2 u

Under GHC 6.8.2 I get the answer 0, under GHC 6.10.1 I get the answer "undefined". Both are wrong, but at least the GHC 6.8.2 one works enough for me to use it. So there are a couple of issues here:

1. fromConstr = fromConstrB undefined in Data.Data is a really bad idea - instead of undefined error "Data.Data.fromConstr" would be a million times better. It took 3 hours to even figure out what library was causing the undefined in a 80 module program! base was not my first guess :-)

2. Ratio used to have a workable fromConstr, now it doesn't. Before it gave the wrong answer. It's all to do with the strictness annotations on :%. The new version means I can't use Uniplate with Haskell Source Exts, which is a really big shame. I have no idea what the fix is.

Trac metadata

Trac field	Value
Version	6.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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