Re: [boost] [spirit][karma] In-place modification of previously parsed content?

Subject: Re: [boost] [spirit][karma] In-place modification of previously parsed content?
From: Hartmut Kaiser (hartmut.kaiser_at_[hidden])
Date: 2009-08-19 14:44:27

> I wonder if it is possible to modify previously parsed content using
> Karma. An example is some text like:
> 
> coordinate (1,  4.15,     1.49,    0.81)  // some comment 1
> coordinate (1,   -19,        4,      -1)  // some comment 2
> 
> Now suppose the numbers are all parsed, and I change the 0.81 to 71.44.
> I want to update the text accordingly:
> 
> coordinate (1,  4.15,     1.49,   71.44)  // some comment 2
> coordinate (1,   -19,        4,      -1)  // some comment 2
> 
> Note how the overall formatting and comments are preserved. The text
> could contain lots of other strings etc. and they would be all left
> untouched. This part - the preservation - is the hard one, and I ask,
> is this possible using Karma?

If Spirit.Qi is for turning unstructured input (most often text/character
streams) into structured (internal) data (most often called parsing) then
Spirit.Karma is for doing the opposite: turning structured (internal) data
into unstructured (external) text/character streams (some people call it
unparsing, we call it generating). Both Qi and Karma use similar grammars to
describe the format of the external representation while using C++ data
structures as the internal representation.

So the answer to your question is: as long as you have/create a format
description for your external textual representation it is possible to use
Karma to generate text matching the required format from your internal data.

See here for a more elaborate higher level description:
http://tinyurl.com/nca9pk.

HTH
Regards Hartmut