http://gamasutra.com/view/news/169296/Indepth_Functional_programming_in_C.php
Anything John writes is well worth reading, this article included. He includes as shout out to D!
"It seems like there is a sound case for a pure keyword in future C/C++ standards. There are close parallels with const – an optional qualifier that allows compile time checking of programmer intention and will never hurt, and could often help, code generation. The D programming language does offer a pure keyword. Note their distinction between weak and strong purity – you need to also have const input references and pointers to be strongly pure."
On reddit: https://www.reddit.com/r/programming/comments/2meuco/john_carmack_on_functional_style_in_c/ https://news.ycombinator.com/item?id=8614253
