[Caml-list] Odd type error reporting

["Christoph Höger" <christoph.hoeger@tu-berlin.de>]

Dear all,

It just took me 30min to figure out a rather simple type-error in my
code. It was complicated by ocamlc's strange error reporting. Consider
this example:

% cat error.ml
type foo = { foo : int }
type bar = { bar : int }
type baz = { f : int -> foo }

let () = { f = fun bar -> { bar } }
% ocamlc error.ml
File "error.ml", line 5, characters 28-31:
Error: This record expression is expected to have type baz
       The field bar does not belong to type foo



ocamlc correctly spots the "bar" in the last line as the source of the
error. However, it says, it is expected to have type "baz", but that is
the surrounding constructor.

In fact, the "correct" error is:

File "error.ml", line 5, characters 26-33:
Error: This record expression is expected to have type foo
       The field bar does not belong to type foo



Obviously, in a perfect world, the wrongly labeled field should be
pointed out as well (kind of a sub-error). However, it seems problematic
that the outermost record-mismatch is reported.

Is this a known bug/feature? Does it change in later versions (I am on
4.02.3 now)?

thanks,

Christoph
-- 
Christoph Höger

Technische Universität Berlin
Fakultät IV - Elektrotechnik und Informatik
Übersetzerbau und Programmiersprachen

Sekr. TEL12-2, Ernst-Reuter-Platz 7, 10587 Berlin

Tel.: +49 (30) 314-24890
E-Mail: christoph.hoeger@tu-berlin.de