+genNonEmptyString :: Gen String
+genNonEmptyString = arbitrary `suchThat` (\s -> ((s /= "") &&
+ (all isAscii s) &&
+ (all isLetter s)))
+
+instance Arbitrary ByteString where
+ arbitrary = pack <$> arbitrary
+
+instance Arbitrary BVal where
+ arbitrary = sized bval
+ where
+ bval :: Int -> Gen BVal
+ bval 0 = oneof [ Bint <$> arbitrary
+ , Bstr <$> arbitrary]
+ bval n = oneof [ Bint <$> arbitrary
+ , Bstr <$> arbitrary
+ , Blist <$> vectorOf n (bval (n `div` 4))
+ , do keys <- vectorOf n genNonEmptyString
+ vals <- vectorOf n (bval (n `div` 4))
+ return $ Bdict $ fromList $ zip keys vals ]
+
+-- getters
+bValToInteger :: BVal -> Maybe Integer
+bValToInteger (Bint x) = Just x
+bValToInteger _ = Nothing
+
+bValToBytestr :: BVal -> Maybe ByteString
+bValToBytestr (Bstr bs) = Just bs
+bValToBytestr _ = Nothing
+
+bstrToString :: BVal -> Maybe String
+bstrToString bval = unpack <$> bValToBytestr bval