From: Frederick Akalin <akalin@akalin.cx>

> At the risk of starting another flamewar, I have another question.  I  
> notice that if I have a record type that's defined in an .mli file, I  
> am able to print objects of that type and see its contents in the  
> debugger.  However, if I make that type abstract (only defining it in  
> the .ml file), I am unable to do so, instead seeing "<abstr>", unless  
> I am in the .ml file where the type is defined.
> 
> Surely this information is available to the debugger from anywhere in  
> the program?  Currently I make most of my types non-abstract simply  
> because it is impossible to debug my programs without being able to  
> check record contents, a practice which I would like to avoid having  
> to do.  I am used to gdb, which prints out all a struct's contents  
> regardless of protected/private modifiers, or Perl, which provides a  
> similar facility with the Data::Dumper module.

To be more precise, the debugger uses information from the .cmi file
to print values. The information is not included in the .cmo file,
even with the -g option. Printing automatically abstract type would
require a new infrastructure, saving type definitions in the .cmo.

Note that an intermediate step would be to declare your definitions as
private: they become semi-abstract (you cannot create values from
outside the module), but you can still print them.

> I am aware that the debugger lets you load printing functions, a  
> facility which I am now exploring.  Although my first impression is  
> that it requires a non-trivial amount of work, both on the coding and  
> debugging side.

This requires some work, but not as difficult as it may seem.
The pretty-printer is very easy to use, particularly Format.fprintf.

Jacques