http://hackage.haskell.org/package/properties-0.0.2 <http://hackage.haskell.org/package/properties-0.0.2>Properties can use QuickCheck properties in the same way than assertions are used, for causal debugging of real programs. It also add an human readable structure for grouping properties for classes or libraries. The properties can then be tested in the instance´s body or in programs as if they were assertions. The main advantage is that the compliance of properties can be done with the complete data range that the real application generates (hopefully, with an pleasant separation of real code and debug code). This is a simple example: stringProperty= [Property <http://hackage.haskell.org/packages/archive/properties/0.0.2/doc/html/Test-Properties.html#t%3AProperty> "length" (\(x, y)-> length (x++y)== length x + length y)] main= do let s= "hello " let s2= "world" print $ s++ s2 `verify <http://hackage.haskell.org/packages/archive/properties/0.0.2/doc/html/Test-Properties.html#v%3Averify>` stringProperty `with <http://hackage.haskell.org/packages/archive/properties/0.0.2/doc/html/Test-Properties.html#v%3Awith>`(s,s2) print "that's all!" It is possible to check quickCheck style properties. The same example with a quickCheck-style property: quickCheckProperty x y= length (x++y)== length x + length y main= do let s= "hello " let s2= "world" print $ s++ s2 `verify <http://hackage.haskell.org/packages/archive/properties/0.0.2/doc/html/Test-Properties.html#v%3Averify>` [Property "stringSumLength" $ uncurry quickCheckProperty] `with <http://hackage.haskell.org/packages/archive/properties/0.0.2/doc/html/Test-Properties.html#v%3Awith>`(s,s2) print "that's all!" The package include a more sophisticated example. I Hope that this would be useful Alberto