Le 28/12/2011 22:45, Steve Horne a écrit :

Yes - AT COMPILE TIME by the principle of referential transparency it always returns the same action. However, the whole point of that action is that it might potentially be executed (with potentially side-effecting results) at run-time. Pure at compile-time, impure at run-time. What is only modeled at compile-time is realized at run-time, side-effects included.
(...)

I hope If convinced you I'm not making one of the standard newbie mistakes. I've done all that elsewhere before, but not today, honest.

Sorry, perhaps this is not a standard newbie mistake, but you - apparently - believe that an execution of an action on the "real world" is a side effect.

I don't think it is.
Even if a Haskell programme fires an atomic bomb, a very impure one, there are no side effects within the programme itself.
If you disagree, show them.

I don't think that speaking about "compile-time purity" is correct.

Jerzy Karczmarczuk