Re: [Caml-list] syntax changes from 3.08 to 3.10

["Nicolas Pouillard" <nicolas.pouillard@gmail.com>]

On 7/11/07, Sebastien Ferre <ferre@irisa.fr> wrote:
> Hi,
>
> moving my application from OCaml 3.08 to 3.10,
> I encountered 2 syntax problems, i.e. syntax errors
> when compiling:
>
> 1. record copy and modification:
>
>    {f x with y = 1; z = 2}
>
> this can be solved by parenthesizing the
> evaluation of the record to be copied.
>
>    {(f x) with y = 1; z = 2}

Yes you now have to put these parentheses.

> 2. object copy and modification in a method:
>
>    {< x = 1; y = 2>}
>
>    OCaml says the first field is a bool instead of an int,
>    which leads me to think it parenthesizes in the following way:
>
>    {< x = (1; y = 2)>}
>
>    In fact, this behaviour is only when compiling with camlp4o:
>
>    ocamlc -pp ocamlp4o ...

Yes that's an awful bug that is already fixed in CVS.

>
>    The work-around I found to implement a copy method is as follows:
>
>    class c =
>      object (self)
>        val x = 0
>        val y = 0
>
>        method copy = (Oo.copy self) # copy_aux
>        method private copy_aux = x <- 1; y <- 2; self
>      end
>
>
> Has anybody encountered the same problem ? Is there a better workaround
> ? Is it a bug ?
>

A better workaround is:

    class c =
      object (self)
        val x = 0
        val y = 0

        method set_x newx = {< x = newx >}
        method set_y newy = {< y = newy >}
        method copy = (self#set_x 1)#set_y 2
      end

But this camlp4 bug is very nasty (perhaps you can try to move these
calls in a file that does not require camlp4o)

-- 
Nicolas Pouillard