[Spirit-general] Closures + Semantic expressions

[joel de g. <dj...@gm...>]

Hello,

The implementation of Spirit's semantic expressions 
(Lambda, argument binding) plus Spirit's closures 
(true local variables) is a very potent mix that, upon
further deliberation, can be applied to other applications
once decoupled and made generic. 

Spirit's closures is a unique facility that is missing in all 
lambda libraries I have seen so far. AFAIK, there are
no known C++ lambda/functional libraries in existence that
can access the *true* closure of functions with local variables
that exist in the hardware stack. True closures is a unique 
Spirit innovation. It is well known that binders in C++ are
your *poor man's* closure in the sense that the bound
arguments are stored as member variables and thus are
not reentrant at all.

Dan and the others have noted that there are many classes
in Spirit that could be decoupled from the framework for
reuse in different contexts. The chset and the symbol table,
for example. I think the closure + semantic expressions are
another sub-framework that might be useful in other applications.
Martijn and Chris suggestion that the semantic expression
sub-framework be used in another context outside Spirit
got me thinking. It is indeed possible!

The implementation of the binders (semantic expressions) 
leveraged the tricks techniques used by the original Spirit
library (e.g. curiously recurring template pattern). It was not
derived from any binder libraries although Spirit itself was
influenced greatly by FC++. To be politically correct, it might
be possible to decouple its front end from the binder engine
such that one can leverage other libraries (e.g Lambda Lib).
Considering the size of Lambda Lib. compared to semantic-
expressions which is just one header + implementation file,
I can keep the original implementation as the default engine.

So, do you think this is something worth doing?
I'll appreciate your comments a lot.

--Joel


_________________________________________
I dedicate Spirit to my dear daughter Kim
   http://www.mikokoro.net/kim.html
_________________________________________