Comment author: administrator

there seems to be a bug printing exceptions. First of all, the
implementations of the module Printexc and of byterun/printexc.c don't
match. E.g.:
exception E of (int * string)
[...]

Right, exceptions that take a tuple of arguments are special-cased
differently in Printexc and in the runtime system. Note however that
the code in the runtime system sometimes goes too far, e.g.

exception E of string list
let () = raise (E ["foo"])

prints

Fatal error: exception Foo.E("foo", 0)

so it's unclear we want to reproduce this bug in Printexc...

Also, "exception E of int * string" would work fine in both printers.

In addition to this we have also complicated applications that sometimes
print out exceptions containing only one string argument without the
contents of the string, e.g.:

exception SomeException of string

Leads to the exception string:

SomeException (_)

instead of:

SomeException ("explanation of error")

I haven't yet managed to reproduce this error reliably. Maybe you have
an idea why this can happen?

How is the printing done? At the toplevel, via Printexc or by the
runtime system? The only case that I know of is at the toplevel:

exception E of string list;;

exception E of string list

let f () = raise (E ["hello"]);;

val f : unit -> 'a =

exception E of int;;

exception E of int

f ();;

Exception: E _.

It's due to the shadowing of the declaration of E. But even in this
case, exceptions that carry a string are special-cased and print
correctly:

exception E of string;;

exception E of string

let f () = raise (E "hello");;

val f : unit -> 'a =

exception E of int;;

exception E of int

f ();;

Exception: E "hello".

Best wishes,

• Xavier Leroy

Comment author: administrator

On Thu, 18 Nov 2004, Xavier Leroy wrote:

In addition to this we have also complicated applications that sometimes
print out exceptions containing only one string argument without the
contents of the string, e.g.:

exception SomeException of string

Leads to the exception string:

SomeException (_)

instead of:

SomeException ("explanation of error")

I haven't yet managed to reproduce this error reliably. Maybe you have
an idea why this can happen?

How is the printing done? At the toplevel, via Printexc or by the
runtime system? The only case that I know of is at the toplevel:
[snip]
It's due to the shadowing of the declaration of E. But even in this
case, exceptions that carry a string are special-cased and print
correctly:
[snip]

It's actually also Failure-exceptions which are sometimes printed
without argument. It happens very rarely, I hope we will be able to
reliably reproduce this problem in a short code snippet. Thanks anyway
for investigating this.

Best regards,
Markus

Comment author: administrator

Waiting for repro case.

Comment author: gerd

I don't have a repro case for Failure, but for Invalid_argument. Separately reported as #4476.

Comment author: @damiendoligez

fixed in 3.10.2+dev2