[Haskell-beginners] quickCheck generation question

[Joe Van Dyk]

On Mon, Oct 10, 2011 at 6:26 AM, Christian Maeder
<Christian.Maeder at dfki.de> wrote:
> Am 08.10.2011 01:40, schrieb Joe Van Dyk:
>>
>> I'm going through the 99 Haskell problems and am trying to write
>> quickCheck properties for each one.
>>
>> -- 3 (find k"th element of a list)
>> element_at xs x = xs !! x
>> prop_3a xs x = (x<  length xs&&  x>= 0) ==>  element_at xs (x::Int) ==
>> (xs !! x::Int)
>
> The definition and test look very similar (basically "=" is replaced by
> "=="). So this seems to test reliability of definitions and Eq instances.
> Such tests should not be necessary. (Testing different implementations for
> equality makes more sense.)

Well, yes, of course.  The point is learning how the tests work, not
the code under test.

Joe