John Carmack on Eclipse performance

[Suliman]

On Tuesday, 1 October 2013 at 12:14:31 UTC, Dicebot wrote:
> On Tuesday, 1 October 2013 at 12:02:29 UTC, w0rp wrote:
>> I'm waiting for Carmack to adopt D already. Barring some 
>> implementation details (GC issues, shared libraries, bla bla) 
>> it's pretty much the perfect language for what he wants to do. 
>> (Fast and functional in parts.) Plus, if anyone could work 
>> around issues or figure out how to do really cool things with 
>> D, it would be Carmack.
>
> He is familiar with D and has shown appreciation for D `pure` 
> functions in his twitter posts.

Link to post? Sorry, but what does 'pure' mean in this content? 
Does it's mean good or bad?