> The printing of Big_int is possible and AFAIK Big_int is an abstract  
> data type.

> let print_big_int (value_big_int:Big_int.big_int) =
>    Format.printf "%s" (Big_int.string_of_big_int value_big_int);;

I see, thanks. If I interpret this correctly, then the same code is
loaded twice. Once in the program to be debugged, once for the printer.

Now I have the following problem: The ADT I want to print uses an
external C library. Ocamldebug refuses to load it, saying: 
(ocd) load_printer ../smath/libsmath.a
Error during code loading: ../smath/libsmath.a is not a bytecode object
file

Any ideas?

Stefan Ratschan