Proposal: Relax rules for 'pure'

[Simen kjaeraas]

Don <nospam at nospam.com> 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.

And my axe!

That is, I support this.

-- 
Simen