Haskell QuickCheck best practices (especially when testing type classes)

Question

I\'ve just started using QuickCheck with a bunch of Haskell code. I\'m behind the times, I know. This question is a two-parter:

Firstly, what are the general best-pr

Answer 1

It's tedious to write the same property for each instance

You don't do this. You write the property once for the class:

class Gen a where
    next :: a -> a
    prev :: a -> a

np_prop :: (Eq a, Gen a) => a -> Bool
np_prop a = prev (next a) == a

Then to test it, you cast to a particular type:

quickCheck (np_prop :: Int -> Bool)
quickCheck (np_prop :: String -> Bool)

Your other questions I can't help with.