Implementing Pure Functions

[Andrei Alexandrescu]

On 6/17/11 1:56 AM, Kagamin wrote:
> Andrei Alexandrescu Wrote:
>
>> This has sparked an interesting discussion, to which I added my
>> bit.
>
> int fun(int a) pure { if (a>  10) writeln("I'm impure); }
>
> As I understand, even if some calls to a function have some
> repeatability properties, this doesn't mean the function is pure. In
> this example fun is obviously impure. Here one can talk about
> allowing to call impure functions from pure ones, but that's a way
> different task.

Right. I gave that example within the context of the discussion, which 
considered purity a path-sensitive property. By that definition, if fun 
is provably never invoked with a > 10, then it's effectively pure.

Andrei