Next step after pychecker

[Paul Rubin]

Philippe Fremy <phil at freehackers.org> writes:
> I would like to develop a tool that goes one step further than
> pychecker to ensure python program validity. The idea would be to get
> close to what people get on ocaml: a static verification of all types
> of the program, without any kind of variable declaration. This would
> definitely brings a lot of power to python.

You know, I've always thought that ML-style type inference is an
impressive technical feat, but why is it so important to not use
declarations?  This is an aspect I've never really understood.