I think you need to forbid access to shared state as well. It's possible to allow it if a strongly pure function calls a weakly pure function in an object that it created, but that seems unnecessarily complex. Actually, that makes me wonder: can constructors be marked pure?
Don Wrote: > Don wrote: > > The docs currently state that: > > > PROPOSAL: > > Drop the first requirement. Only one requirement is necessary: > > > > A pure function does not read or write any global mutable state. > > > > Wow. It seems that not one person who has responded so far has > understood this proposal! I'll try again. Under this proposal: > > If you see a function which has mutable parameters, but is marked as > 'pure', you can only conclude that it doesn't use global variables. > That's not much use on it's own. Let's call this a 'weakly-pure' function. > > However, if you see a function maked as 'pure', which also has only > immutable parameters, you have the same guarantee which 'pure' gives us > as the moment. Let's call this a 'strongly-pure' function. > > The benefit of the relaxed rule is that a strongly-pure function can > call a weakly-pure functions, while remaining strongly-pure. > This allows very many more functions to become strongly pure. > > The point of the proposal is *not* to provide the weak guarantee. It is > to provide the strong guarantee in more situations.
