Re: [boost] [proto] Calculator Arity Transform and function varargs

From: Eric Niebler (eric_at_[hidden])
Date: 2007-08-27 13:13:34

Eric Niebler wrote:
> (Sorry for the delay, I've been away on vacation.)
> 
> Felipe Magno de Almeida wrote:
>> Hi,
>>
>> I can't make it out how to do the arity transformation for
>> proto::functions varargs too.
>> Could anybody shed some light?
> 
> I think I may need more information about what you're trying to do. 
> There is a (rather advanced) example of using the fold transform on a 
> proto::function with varargs here: http://tinyurl.com/2l9srv. Does that 
> help any? When dealing with varargs, the fold and reverse_fold 
> transforms are especially handy because they iterate over the sequence 
> of children nodes for you -- you don't have to worry about how many 
> there are. So if you can express your transform using fold, it'll make 
> life easier.

Oh, I just noticed from the subject line that you're looking at the 
calculator arity transform. There is an example that shows how to do the 
arity calculation using fold and vararg. Look for CalculatorGrammar here:

http://svn.boost.org/trac/boost/browser/trunk/libs/xpressive/proto/example/calc3.cpp

It is heavily commented, and shows a couple of different ways to tackle 
the problem.

HTH,

-- 
Eric Niebler
Boost Consulting
www.boost-consulting.com
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