Pure and Structs

[Chad J]

Walter Bright wrote:
> dsimcha wrote:
>> Will pure eventually be expanded to deal with more cases where the
>> referential
>> transparency and inherent thread-safety of a function is obvious to
>> humans,
>> like these, or is this simply asking too much?
> 
> If it can be proven (and it can in your example) it can be pure.

I'm curious, how difficult is it to mechanically prove/disprove purity
in the general case?

I thought this was going to be one of those things like escape analysis,
where we'd have to settle for a subset of the provable cases for the
sake of easy of implementation.