Wikipedia purity example and discussion

[Vladimir Panteleev]

A while ago, someone added an example with pure functions to Wikipedia's D  
article:

http://en.wikipedia.org/wiki/D_(programming_language)#Functional

Someone on the talk page asked why does the program compile despite that  
mySum accesses a variable in its enclosing function:

http://en.wikipedia.org/wiki/Talk:D_(programming_language)#Purity_of_mySum_function_in_the_.22Functional.22_section_.281.1.4.29

I replied with:

> The code indeed compiles. I think that the idea is that nested functions  
> have a hidden argument - a pointer to their enclosing scope (main's  
> local variables). However, that doesn't explain why the code continues  
> to compile when pivot is moved outside main(), or if you add a call to a  
> non-pure function in mySum - these sound like compiler bugs.

I don't know much about purity, so I thought someone could shed some light  
on this?

-- 
Best regards,
  Vladimir                            mailto:vladimir at thecybershadow.net