[Types-sig] Issue: definition of "type"

[Martijn Faassen]

Paul Prescod wrote:
> Martijn Faassen wrote:
[snip]
> > Doesn't this rely on run-time information? How would a type system deal
> > with this? I suppose I'm entering the domain of interfaces now...
> 
> Yes, that is the role of interfaces. Nobody has yet suggested that the
> code you described would be type-safe. The two doSomething methods are
> unrelated.

I understood that, but I am saying that this type of thing is quite
common in Python, and I was reacting to what you said here:

> ...because I would like to
> think that all of the code out there with class statements is *already*
> defining a bunch of types. A minority of it depends on runtime
> information and we can easily detect those cases.

I was pointing out this common idiom in Python as an argument against
your statement that a minority depends on runtime information (that we
can easily detect). Lots of Python code depends on this idiom so it's
good to address it.

Regards,

Martijn