[sv-ec] Streaming operator and Mantis 1707

Shalom has pointed out that Mantis 1707 conflicts with one
of the examples in the existing LRM text that would be
unaffected by it.  I thought it was just an editorial
fix, but it ain't.  I tried the attached testcase in 
those simulators I can use that know how to do {<<{}}.
None of the implementations matches what I would 
expect from 1707 and my own intuition.  However, 
the implementations are in almost total disagreement
about the answer, so I'm not the only one who is lost.

Can folks please try out this example, and look 
critically at the results of the operations where
a stream is [un]packed to/from a vector that's 
wider than the stream?  Left-to-right packing

  too_big = {>>{a,b,c}};

gives the results I expect in each implementation
I tested.  All other operations where the vector
is bigger than the stream give conflicting results.
It would be nice to reach a consensus before I try
to fix the examples (and, possibly, fix 1707 too).
Implementations are sufficiently divergent now that
we lose nothing by defining the behaviour we want,
rather than a behaviour that maintains backward
compatibility.

Thanks
-- 
Jonathan Bromley



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