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

Subject: [boost] [spirit][karma] In-place modification of previously parsed content?
From: Carlos Rafael Giani (e0325834_at_[hidden])
Date: 2009-08-19 13:26:50

Hello,

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?