On Mon, Feb 19, 2018 at 9:24 PM, Steven D'Aprano
<steve+comp.lang.pyt...@pearwood.info> wrote:
> On Mon, 19 Feb 2018 09:40:09 +0100, Alain Ketterlin wrote:
>
>> Tim Delaney <timothy.c.dela...@gmail.com> writes:
>>
>> [...]
>>> As others have said, typing is about how the underlying memory is
>>> treated.
>>
>> No. It is much more than that. Typing is about everything you can say
>> about a given statement.
>
> "Everything"? Truly *everything*?
>
> Given:
>
> # engage the type system somehow...
> # declare a, b, c: non-negative integers
> a = abs(int(input("Give me an integer")))
> b = a*a
> c = (a+1)*(a+1)
>
> can you give me an example of a type-system which is capable of telling
> me that:
>
> if (c - b) % 2 == 1:
> print("hello world")
> else:
> fire_missiles()
>
> will never fire the missiles?
>
> I'd be impressed enough with a type system that knew that a%2 was always
> 0 or 1, although I suppose there could be some that already know that.
>
> Hell, I'd even be impressed if it could tell that c was not zero...
>
A type system, per se? I don't think so. But static analysis CAN
figure out that sort of thing (obviously, since we as humans can do
it), and I wouldn't be surprised in the least if tools like Coverity
could detect this.
ChrisA
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