Hi Mazoyer,
The IDL Workbench does not come with something like that. The closest to that will be the view in the Workbench called Outline, where the structure of the code can be seen.
Having said that, please, take a look at the IDL Google Newgroup:
http://groups.google.com/...ad/db7372a8fbd4a89f#
The thread is called "IDL routines dependencies map make", which I think you will fine very interesting and possible useful in your case.
Cheers,
Fernando
Exelis VIS