Andreas C. Doering <[EMAIL PROTECTED]> writes:
>
> I would like to have a comparison instruction that compares the internal
> reference of two objects.
> Let's call it "req".
>
> req :: a -> a -> Bool
>
> -- of course it is an equivalence operation
> req x x = True
> req x y = req y x
> (req x y) && (req y z) ==> req x z
>
> req x y = false does NOT imply that x and y are different, only that
> they are represented differently.
>
Constructive/destructive ;-) proposal;
> referentially_equal :: a -> a -> IO Bool
Because it means interaction with the real world of implementation.
Perhaps put it in IOExts.
Then one might go along to define (for oneself):
> req :: a -> a -> Bool
> req a b = unsafePerformIO (referentially_equal a b)
But one should be forced to make oneself aware of the unsafePerformIO inside,
and of the non-standard language features this implies ...
Cheers,
Wolfram
