Excerpts from christophe.troestler+ocaml's message of Mon Jan 28 17:06:10 +0100 2008:
> On Mon, 28 Jan 2008 15:25:12 +0000, Jon Harrop wrote:
> > 
> > So you write a "use" binding:
> > 
> >   let read_first_line file =
> >     use ch = open_in file in
> >     input_line ch
> > 
> > and it gets translated into:
> > 
> >   let read_first_line file =
> >     let ch = open_in file in
> >     try input_line ch finally
> >     ch#dispose
> > 
> > where the "dispose" method that was automatically inserted at the end of the 
> > scope of the "use" binding calls "close_in" in this case to deallocate the 
> > external resource (a file handle in this case but it could be anything with a 
> > dispose method).
> 
> What is wrong with
> 
>    let read_first_line file =
>      with_open_in file begin fun ch ->
>        input_line ch
>      end

This  code  has  nothing  wrong but with_open_in (even if it's very useful) is
not resource safe. This is because the in_channel can escape it's scope.

| let ch = with_open_in file (fun x -> x) in
| input_line ch

This program is obviously wrong but still show that with_open_in is not safe.

Cheers,

-- 
Nicolas Pouillard aka Ertai