[Caml-list] [Batteries or Camlp4] Functionaly updating several fields in an object

[Ivan Gotovchits <ivg@ieee.org>]

I do not know whether the following behaviour is a bug or a feature, so
I've decided to consult with a community.

Given a simple definition:

let create ()  = 
object
  val a = []
  val b = []
  method step = {< a = a; b = b; >}
end

when compiling using batteries extensions:

ocamlfind ocamlc -c -package batteries.syntax -package lablgtk2
-package lablgtk2.init -package oUnit -package threads -package uuidm
-syntax camlp4o -thread -package batteries -syntax camlp4o -I +gsl -I
+res -I +xml-light -I +lablgtk2 -I gui -o gui/bug.cmo gui/bug.ml

I'm receiving the following error:
File "gui/bug.ml", line 7, characters 10-11:
Warning S: this expression should have type unit.
File "gui/bug.ml", line 8, characters 6-11:
Error: This expression has type bool but an expression was expected of type
         'a list

It seems that compilet thinks that something like this:
«a = begin a; b = b end».

After disabling syntax extension everything is ok. 

So the questions:
1) Is this a bug? If not, then how to overcome this unwanted behaviour?
2) If this is a bug? What must be blamed: camlp4 or Batteries?


Thanks in advance, for any comments!

P.S. My setup:
OS: Debian Squeeze 6.0.5
Objective Caml: 3.11.2
Batteries: 1.2.2-1




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