Re: P: single assignment semantics

[Andre Beck <abeck@xxxxxxxxxxxxx>]

Alex Rousskov wrote:
> Thus, depending on the design, a proxy may continue to read response
> body while the service is doing its thing and the interpreter instance
> is waiting.
>
> In fact, in most cases, a complete body will _not_ be available at any
> single time -- it is just too big to cache (the service can cache the
> body if it needs to, but the proxy may not).

I agree and that's in fact why I think P programs should not be allowed 
to reference message bodies. In my opinion, P programs should only serve 
as high-level filters that invoke OPES services based on message header 
values (e.g. HTTP content-type) and maybe system and environment 
variables (e.g. system time). If a P program triggers the execution of a 
service, then the service logic within that service can evaluate all 
message properties including the message body to determine if there is a 
need to process the message. I don't think it's a good idea to move that 
kind of service logic into P programs. By restricting P programs in this 
way we would also render the copy vs. reference question essentially a 
non-issue simply because we can assume that message header values are 
always small and copy operations would not have a significant 
performance impact. I would therefore favor the 'programmer-friendly' 
constant approach over the macro approach or any combination thereof.

-Andre