Printing PEG structure

I am curious.  I know that the grammar for Spirit generates a kind of
bytecode at compile time that the parse functions can go over to do
the actual parsing (again, optimized at compile time).  I am curious,
would it be possible to create such a function that goes over that
bytecode/typetree of Qi/Karma and can print out the PEG string
representation of what the parsing does?  For terminals it does not
know about would need to override a function or so that lets it print
out its representation.

Would be great for debugging though.

rule<...> r1, r2;
r1 = int_ >> space >> double_%',';
r2 = r1 | (lit('"')>>*~char_('"')>>lit('"'));
r1.name("r1");
r2.name("r2");

ostringstream o;
peg_string(o, r2);
o.str(); // returns:

r2 = r1 | ('"' (~'"')* '"')
r1 = int space double (',' double)*
int = /* however this is defined */
space = ' '|'\t'|'\r'|'\n'
double = /* however this is defined */

Or something like that.  Does not need to be pretty, just get the
point across, would be great to toss into documentation for a created
parser too.

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