Re: [Boost-users] [Review] Phoenix V3: mini-review starts February19th

Subject: Re: [Boost-users] [Review] Phoenix V3: mini-review starts February19th
From: Robert Ramey (ramey_at_[hidden])
Date: 2011-02-02 13:21:45

Eric Niebler wrote:
> (Cross-posting for now, but please follow up on boost-users only.)
>
> On 2/3/2011 12:06 AM, Robert Ramey wrote:
>> I've been studying proto/fusion/phoenix.  Becoming familiar with
>> this stuff takes quite an effort.  It's quite interesting though.
>> And it seems ideal for a project I want to do.  But I do have one
>> question:
>>
>> phoenix/Function objects
>> Functional/
>> Proto/
>> PolymorphicFunctionObject
>> ?
>>
>> All seem to address function objects.  There seems to be a lot of
>> overlap and it's not clear to me which I should be using for what.
>> That is, each library seems to address function objects from a
>> different perspective, but there is not summary which contrasts
>> them.  I need a "function object library Decoder Ring".  Are
>> there any documents which would help me out?
>
> Lots of libraries define function objects or tools for creating them.
> That's true for Phoenix and Proto (both tools for creating function
> objects). Phoenix helps you define general purpose function objects
> in-place (lambdas). Proto helps you define function objects
> specifically for manipulating expression trees (grammars w/ semantic
> actions).
>
> PolymorphicFunctionObject is a concept that function objects must
> model if they are to be usable with boost::result_of. Function
> objects created by Phoenix and Proto all model
> PolymorphicFunctionObject.
>
> I don't know anything about boost/functional.
>
> HTH,

Amazingly, this DOES help.

I should add boost/function to the above list which is also a library
for defining function objects.  A cursory examination would suggest
to this humble reader that:

boost/bind included in boost/lambda
boost/lambda & boost/function included in boost/phoenix
proto - able to use function objects defined by phoenix but not those 
defined by boost/function
proto - also used to define function objects specifically for proto DSEL .

As a strategy for implementing my own pet DSEL application I wanting to

a) define types of the objects that I'm dealing with - no conceptual 
problems here.
b) define concepts on the above types to catch errors - no conceptual 
problems here but somewhat harder.
c) define functions and/or function objects which use variables of the above 
types. At this point the question arises as to which library would provide 
the best "templates" to build these funtions/function_objects.  This was the 
motivation for my question.
d) define concepts on c) to catch usage errors
e) build some tests/examples using the above to verify that the whole thing 
looks more or less natural and not too cryptic to be usable.
f) build a "proto-layer" which implements the DSEL using the the function 
objects defined above.  It would have its own set of functions with similar 
names to c) above which would return expressions rather than do any real 
work.  That is, c) above would define "language semantics", while proto 
would define
"language syntax" in terms of c) above.

A large part of the motivation here is to separate things into "conceptual 
layers" so I don't have to
the whole thing in my head simultaneously. At my age, internal stack 
overflow is a serious concern.

I'm just curious if I'm on the right track here.

Robert Ramey