Proposal: Relax rules for 'pure'

[Don]

Pelle wrote:
> On 09/22/2010 10:13 AM, 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.
> 
> Will this allow member functions to be weakly pure? As in, only touches 
> its own state.
> 
> Because that would be useful.
Yes.