This looks like a bug in OCaml (which is in my experience rare!), and
an insidious one at that.
I defined:
let print_event = function
| StartElement -> print_string "StartElement "
| EndElement -> print_string "EndElement "
| Text -> print_string "Text "
| EndOfDocument -> print_string "EndOfDocument "
and changed the failing case to:
| (ev, name) as foo -> begin
print_event (fst foo); print_endline (snd foo);
print_event ev; print_endline name;
print_newline ();
if test foo then handle_next a else a
end
and look at the garbage OCaml prints out:
StartElement toto
StartElement toto
StartElement titi
EndElement titi
EndOfDocument toto
EndElement toto
Exception: Failure "Unexpected end of source".
(Each pair of lines should be identical.) This is in 3.11.2 on Ubuntu
x86_64, and happens with both bytecode and compiled code.
See if you can shrink down your example while maintaining this bug and
then file a bug report: http://caml.inria.fr/mantis/my_view_page.php
On Fri, Jan 6, 2012 at 11:41 AM, DelPhiNus <[email protected]> wrote:
> Considering the sample code below that contains non-functional stuff
> that mimics a simple XmlScanner from my company.
>
> type event = StartElement | EndElement | Text | EndOfDocument
>
> let cur_name = ref None
> let name () = match !cur_name with None -> failwith "None" | Some name
> -> name
> let next it =
> match !it with
> | [] -> failwith "Unexpected end of source"
> | hd :: tl -> it := tl; cur_name := Some (snd hd); fst hd
>
> let read_section_while source test f a =
> let rec handle_next a =
> match next source, name () with
> | EndOfDocument, _ -> failwith "Unexpected end of
> document"
> | Text, _ -> handle_next (f a "Text")
> | StartElement, "titi" -> handle_next (f a "Start titi")
> | EndElement, "tata" -> handle_next (f a "End tata")
> | xml -> if test xml then
> handle_next a else a
> in
> handle_next a
>
> let source = [
> (StartElement, "toto");
> (StartElement, "titi");
> (EndElement, "titi");
> (StartElement, "tata");
> (EndElement, "tata");
> (EndElement, "toto");
> (EndOfDocument, "dummy")
> ];;
>
> read_section_while (ref source) ((<>) (EndElement, "toto")) (fun a x -
>> x :: a) [];;
>
> ==== END SAMPLE ===
>
> I have an exception "Unexpected end of source" while the code was
> supposed to stop normally on (EndElement, "toto")
>
> The same code works as expected if I just change slightly the default
> pattern:
> | ev, name -> if test (ev, name) then handle_next a else a
> instead of:
> | xml -> if test xml then handle_next a else a
>
> Again, the same code works if I make the tuple resulting from (next
> it, name ()) just before the pattern matching:
> let x = next source, name () in match next x with
> instead of:
> match next source, name () with
>
> From my point of view, I thought that there was no fundamental
> difference between the code that works and the code that fails. Maybe
> I missed something...
>
> I am using Ocaml 3.11.0 and I don't plan to update for the moment
> since I am experiencing 3rd party library link problems as soon as
> something change in the Ocaml+MinGW+Cygwin+FlexDLL toolchain.
>
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