[Ur] garbage collection

[Adam Chlipala]

Gergely Buday wrote:
> the FAQ writes:
>
> "Ur/Web provides much better run-time performance than any competing
> system. Server-side components are native code and don't use garbage
> collection."
>
> What does it use for memory management then?
>    

The compiler uses region-based memory management, driven entirely by 
inference.  Worst case, all memory may be freed at once at the end of 
each page request.  There is no mechanism for heap-allocated data to 
outlive single page requests.

The compiler also infers some intermediate regions based solely on type 
information.  For instance, SQL query loops run only for their side 
effects often have their bodies placed inside regions.