Re: [boost] [msm] Review

Subject: Re: [boost] [msm] Review
From: Adam Merz (adammerz_at_[hidden])
Date: 2009-12-07 06:15:56

So you say:

David Bergman writes:
> 
> On Dec 6, 2009, at 3:37 AM, Christophe Henry wrote:
<snip>
> > > 5. MSM has eUML, which I have *not* used, to simplify the machine
> > > specification.
> > 
> > I'd also count it as an important interface difference.
> 
> I think it is, but have not tried it out (unfortunately.)
> 

Then later follow that up with:

David Bergman writes:
> 
> But, the interfaces are similar enough not to have the audience go "holy
> crap" when seeing the other after the first.
> 
> But for "wildly different interfaces", I would except something along the
> lines of Regex vs Xpressive, not two tools using the same C++ constructs for
> virtually everything.
> 

Huh..?

How is an EDSL (which I think constitutes a "wildly different interface" by most 
people's standards) that results in faster execution [1] not *exactly* analogous 
to the Regex vs. Xpressive comparison that you've brought up multiple times? Is 
it because eUML is optional, given Msm's support for multiple frontends? I can 
only point out that in addition to "static Xpressive" (the EDSL), Xpressive also 
contains "dynamic Xpressive," whose interface is extremely similar to Regex, 
probably intentionally so (indeed, I suspect this was lauded during Xpressive's 
review, not criticized).

eUML makes up *~75%* of Msm's code and ~30% of Msm's documentation; metrically, 
it's obviously an extremely significant part of Msm, and is probably what 
warranted a major version increment between Msm versions 1.2 and 2.0. And yet 
despite not having used it, you've been very vocal about the supposed lack of 
differences between Msm's and StateChart's interfaces/representations. This 
seems to me misguided at best...

I suspect that your contrast between Msm and StateChart has been tainted by your 
use of Msm's "standard" frontend. I could be way off here, but my impression 
from the Msm documentation is that the standard frontend exists mostly for 
backwards compatibility with 1.x code and to support older compilers, and that 
eUML is the recommended frontend for new FSMs on supported compilers. If so, I 
would suggest reexamining Msm from a fresh perspective, using eUML; now, given 
*that* interface and the very substantial implementation differences, would you 
still argue that Msm and StateChart are not different enough to warrant the 
inclusion of both into Boost?

[1] 
http://svn.boost.org/svn/boost/sandbox/msm/libs/msm/doc/index.htm#_Performance