use pureness in a sentence.
How did you contribute to the pureness of front page?
Having properties like immutability and pureness in your language makes it lot easier to trust your code and to reason about it.
You really can't express immutability and pureness in C++, because you can still modify global variables and do any kind of IO everywhere, regardless of const.
Introducing Laziness, pureness and static typing into the JS world is a much bigger challenge.