Hi, all, I found derive + quickCheck very useful but I came across some problems. I used derive to derive instance of Arbitrary immeditaely, but sometimes the sample is non-terminating, which I mean the result is very very big. I used samples <- take 10 <$> sample' in ghci to test the result, it's non-terminating.. another problem is that $(derive makeArbitrary ''JValue) uses reify, so I can not see the generated code, any better way to have a look at the generated code in ghci? my sample code {-# LANGUAGE FlexibleInstances ,MultiParamTypeClasses ,GeneralizedNewtypeDeriving ,FunctionalDependencies ,TypeSynonymInstances ,TemplateHaskell #-} module JsonParse where import Text.ParserCombinators.Parsec import Text.Parsec.String() import Control.Applicative hiding ( (<|>) , many, optional ) import Control.Monad import Test.QuickCheck -- unGen, sample -- import Language import Data.DeriveTH import Data.Binary import Data.Derive.Arbitrary import Language.Haskell.TH import Language.Haskell.TH.Syntax data JValue = JString String | JNumber Double | JBool Bool | JNull | JObject [(String, JValue)] -- | JArray [JValue] -- deriving (Eq,Ord,Show) $(derive makeArbitrary ''JValue)