Next step after pychecker

[Francis Girard]

To complete Philippe's answer :

As Bird and Wadler continue :

"The major consequence of the discipline imposed by strong-typing is that any 
expression which cannot be assigned a "sensible" type is regarded as not 
being well-formed and is rejected by the computer before evaluation. Such 
expression have _no_ value: they are simply regarded as illegal."

But Skip, I am sure that you can easily find an example by yourself. For 
example, replace "+" by a function that does different things depending on 
its argument type.

Francis Girard

Le mercredi 2 Février 2005 10:27, Philippe Fremy a écrit :
> Skip Montanaro wrote:
> >     Francis> "Every well-formed expression of the language can be
> > assigned a Francis> type that can be deduced from the constituents of the
> > Francis> expression alone." Bird and Wadler, Introduction to Functional
> > Francis> Programming, 1988
> >
> >     Francis> This is certainly not the case for Python since one and the
> >     Francis> same variable can have different types depending upon the
> >     Francis> execution context. Example :
> >
> >     Francis> 1- if a is None:
> >     Francis> 2-   b = 1
> >     Francis> 3- else:
> >     Francis> 4-   b = "Phew"
> >     Francis> 5- b = b + 1
> >
> >     Francis> One cannot statically determine the type of b by examining
> > the Francis> line 5- alone.
> >
> > Do you have an example using a correct code fragment?  It makes no sense
> > to infer types in code that would clearly raise runtime errors:
>
> On the contrary, the point of type inference is to detect such errors.
> If the program was always well-formed, there would be no point in
> developing a type inference tool.
>
> 	Philippe