Paper acknowledges positively D's approach to purity (locally pure)

[Bill Baxter]

On Fri, Sep 19, 2008 at 8:31 PM, Bruno Medeiros
<brunodomedeiros+spam at com.gmail> wrote:
> Andrei Alexandrescu wrote:
>>
>> bearophile wrote:
>>>
>>> Andrei Alexandrescu:
>>>>
>>>> It's a great honor and validation to be acknowledged in a paper of
>>>> such quality and to see D's approach to purity not only mentioned,
>>>> but in praise terms nonetheless (section 9).
>>>
>>> It seems to contain some comments that are not a praise too:
>>>
>>>> While this approach avoids the need to eliminate mutable state and
>>>> determinism from the global scope, there is a substantial cost in
>>>> expressivity as it prevents pure functions from making any use of
>>>> impure functions and methods. The result is essentially of a
>>>> partition of the program into imperative and purely functional
>>>> portions, whereas our approach allows pure functions to make full
>>>> use of the rest of the program, limited only by the references they
>>>> hold.<
>>
>> Any paper will mention the disadvantages of related work in the pertinent
>> section. I'm not worried about that at all. Their system is more expressive
>> but also considerably more complex. That's not necessarily bad, it's a
>> different point in tradeoff space.
>>
>
> I haven't yet read the whole paper, haven't had the time yet, but, are we
> really restricted to the "Functions marked with the pure keyword must have
> only invariant arguments, can only read invariant global state,
> and can only call other pure methods." ?
> Don and I discussed an idea some time ago, called partially pure functions
> (aka locally pure, aka contextually pure):
> http://www.digitalmars.com/d/archives/digitalmars/D/Idea_partially_pure_functions_70762.html
> which would lift some of those restrictions, in a way that is safe and
> sound, thus allowing more expressiveness (significantly, IMO).

The funny thing is that D's pure hasn't been implemented yet.  Walter
added the keyword to the compiler, but I'm pretty sure it still
doesn't do much of anything useful.  I guess the fine paper was
referring to the spec?

--bb