[Rd] How to access to internal header files

[Sebastian Fischer]

Dear R-devel Mailing List,

I would like to get a better understanding of R's internal structures by 
using R's
C API. For that I would like to have access to all the C header files 
that are listed
here: https://github.com/wch/r-source/tree/trunk/src/include. (i.e. I 
want to e.g.
#include <Defn.h>

However when I install R, there is only a subset of those header files 
available
on my system. While I am aware that files like Defn.h are not intended 
to be used by
R Extensions, I assume there must be some way to configure R's 
compilation to make
these definitions available for my exploration of the language.

I would appreciate any help.

Best regards

Sebastian Fischer