Re: FWD:Re: refactoring

David Abrahams wrote:
> Joel de Guzman <[email protected]> writes:
> 
> 
>>WRT templates and the C++ type system, my current thinking is that
>>I need an embedded runtime interpreter specifically geared to
>>handling the C++ meta template language. It would be a minimalist
>>FP language similar to scheme/lisp. 
> 
> 
> Sorry, I can't picture where you'd need this, or what you'd use it
> for.  More detail, please?

Hmmm... Ok, I'll give it a shot:

The C++ meta template language is a complete FP language that is
executed (interpreted) at compile time one way or another. The
advent of modern c++ and especially template meta programming
makes me think that an adhoc solution to "interpreting" this
language is no longer adequate. IMO, an elegant way to address
this is to actually formalize the compile time interpreter.

A template class can be modeled like a function with multiple
arguments (template parameters) and multiple returns (typedefs).
Types are values in the POV of the compile time interpreter.
The notion of a "metafunction" will be just an ordinary function
in the viewpoint of the compile time interpreter. Partial/full
specializations will be cased and pattern matched like in haskell
(http://www.haskell.org/tutorial/patterns.html).

Imagine, for example, how TMP code such as MPL and Boost libraries
in general, will benefit from actually having it interpreted by
the formalized compile time interpreter. We can provide optimized
intrinsics specific to, say, MPL and type_traits, that would
be "compiled" instead of "interpreted" in the POV of the meta
domain. Such would give dramatic improvements in parse/compile
time.

Regards,
-- 
Joel de Guzman
http://www.boost-consulting.com
http://spirit.sf.net