Why isn't purity & co. inferred for all functions?

[Paulo Pinto]

Am 12.05.2012 05:33, schrieb Walter Bright:
> On 5/11/2012 4:48 PM, Trass3r wrote:
>>> I thought Purity was marked in the mangled name, so that should give
>>> a link
>>> error.
>>
>> Good point.
>
> Doesn't work if any modules declare:
>
> extern int foo();

Those functions would always be considered impure, unless the programmer 
says otherwise in the extern declaration.