Re: [Caml-list] Simple exception - different behaviour between toplevel and compiled

[David Allsopp <dra-news@metastack.com>]

> On 19 Aug 2015, at 00:41, Oliver Bandel <oliver@first.in-berlin.de> wrote:
> 
> Hello,
> 
> 
> using the attached files (executing testexc,bash)
> I got different results between toplevel and compiled:
> 
> =====================================================
> Testcase A
> exception A of int * int
> let _ = raise ( A(3,4) )
> Exception: A (3, 4).
> Fatal error: exception Exca.A(3, 4)
> Fatal error: exception Exca.A(3, 4)
> Testcase B
> exception B of (int*int)
> let _ = raise ( B(3,4) )
> Exception: B (3, 4).
> Fatal error: exception Excb.B(_)
> Fatal error: exception Excb.B(_)
> =====================================================
> 
> So just adding parantheses in a definition of an exception
> yields in these differing results, with not-shown exception-values.
> 
> IMHO looks like a case for the bugtracker...

There's no requirement for the toplevel and the compilers to behave the same way for reporting the exception. The output, for example, also differs in the way the exception message is formatted, there's no 'Fatal error:' and so on - do you want that to be a bug too?

The toplevel has access to typing information which is not available to ocamlc/ocamlopt (the runtime only knows the name of the exception - beyond that, it's just presented with a standard variant block). I haven't got a compiler to hand, but I think you'll also see differences if you use a variant instead of numbers (ocaml will display the constructor name, the compilers will display its constructor number) and I think you'll also see the same output as the compilers if you compile excb.cmo and then #load it in the toplevel.

It's not normal to want to terminate your compiled program with an uncaught exception, hence the simpler default exception printer in compiled code. If you really want the exception printed accurately, you can register a printer (see Printexc.register_printer).


David