Memory allocation purity

[Andrei Alexandrescu via Digitalmars-d]

On 5/15/14, 2:52 PM, Timon Gehr wrote:
> On 05/15/2014 08:03 PM, Andrei Alexandrescu wrote:
>>>>
>>>> Purity of allocation is frequently assumed by functional languages
>>>
>>> Examples?
>>
>> cons 1 2 is equal to cons 1 2
>> ...
>
> I don't see anything whose specification would need to mention
> 'allocation'.

That's the point. There's no specification of allocation - the evaluator 
may create two lists or reuse the same, and it's all transparent.

>>>> because without it it would be difficult to get much work done.
>>>
>>> Why?
>>
>> It's rather obvious. You've got to have the ability to create new values
>> in a pure functional programming language.
>
> This kind of operational reasoning is not essential. Of course, in
> practice you want to evaluate expressions, but the resulting programs
> are of the same kind as those of a non-pure language, and can do the
> same kind of operations. There is not really a distinction to be made at
> that level of abstraction.

I'm afraid I got lost here.


Andrei