Simen Kjaeraas:
Absolutely. But whether purity should be the default or not is orthogonal to this.I would have preferred opt-out purity to opt-in, but it's not exactly make or break.
The colourful Erik Meijer says that specifying what functions are not pure is better than specifying what functions are pure:
http://www.youtube.com/watch?v=z0N1aZ6SnBk#t=54m53s Bye, bearophile
