You might as well say that any language takes as input The Universe and returns a new Universe (perhaps also adjusting for time, if the program gives output dur

You might as well say that any language takes as input The Universe and returns a new Universe (perhaps also adjusting for time, if the program gives output during the execution). See? Totally referentially transparent. But not interesting. Like he says, the technique/viewpoint is already known in FP. But in certain languages you have more control over it than others.