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

[Gabriel Scherer <gabriel.scherer@gmail.com>]

It appears to be a parsing bug in the 3.11 version of Camlp4. It
happens neither with 3.10.2 or with more recent version.
(I was lucky to find a machine with 3.11.2 installed; it's good to
have rarely-updated servers around)

Steps to reproduce:
  camlp4o -str 'let _ = {< a = a; b = b >}'
Observed result:
  {< a = (a; b = b); >}

Upgrading to a more recent version of OCaml would solve your problem.
Otherwise, not using syntax extensions is also fine.

On Tue, Oct 23, 2012 at 2:24 PM, Ivan Gotovchits <ivg@ieee.org> wrote:
>
> 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
>
>
>
>
> --
>          (__)
>          (oo)
>    /------\/
>   / |    ||
>  *  /\---/\
>     ~~   ~~
> ...."Have you mooed today?"...
>
> --
> Caml-list mailing list.  Subscription management and archives:
> https://sympa.inria.fr/sympa/arc/caml-list
> Beginner's list: http://groups.yahoo.com/group/ocaml_beginners
> Bug reports: http://caml.inria.fr/bin/caml-bugs