dynamic classes and duck typing

[Walter Bright]

dsimcha wrote:
> My biggest gripe about static verification is that it can't help you at all with
> high-level logic/algorithmic errors, only lower level coding errors.  Good unit
> tests (and good asserts), on the other hand, are invaluable for finding and
> debugging high-level logic and algorithmic errors.

Unit tests have their limitations as well. Unit tests cannot prove a 
function is pure, for example.

Both unit tests and static verification are needed.