Re: [Boost-users] creating lambda expressions incrementally

From: Felipe Magno de Almeida (felipe.m.almeida_at_[hidden])
Date: 2006-10-18 15:44:41

On 10/17/06, Arnaldur Gylfason <arnaldur.gylfason_at_[hidden]> wrote:
>
> Hi,
>
> I´m writing a simple expression parser in boost::spirit that can parse a
> string like "_1 + _2" or "log(_1)" and return a function object that does
> just that.
> I used boost::lamda for that and return it as boost::function object.
> Now I want to parse compositions like "sqrt(_1*_1 + _2*_2)" or "(_1 +
> _2)*_2" etc. It is easy to parse this of course but I have to create the
> corresponding function incrementally (in a loop or recursively)
> and that means I have to keep incremental lambdas until the whole expression
> has been created.
> I can not store them as boost::function since they do not work with lambda
> operator overloading (apart from the fact that it would be too costly).
> I need a lambda type for these intermediate lambda objects. I guess the auto
> type specifier would solve this but when will that be available I wonder?
> The typeof seems to provide a solution though. I was just trying it and it
> seems to work!
> Am I on the right track or am I overlooking something? If anyone knows a
> better solution please tell me!

You could do it using expression templates. It should be quite easy to
do and very efficient if you aren't going to need to do type-erasure.

>
> cheers
>
> Arnaldur Gylfason

-- 
Felipe Magno de Almeida