Re: [Caml-list] use of ";;" when teaching Ocaml

[David House <dhouse@janestreet.com>]

[-- Attachment #1: Type: text/plain, Size: 2163 bytes --]

That's true, although it's probably a little easier to spot a missing ;;
than a non-missing trailing ;.

I expect that on balance you'll have better errors more often with using
;;. So it seems sensible to use it for teaching beginners. Once you're an
old hand like Mark Shinwell, you can make up your mind whether it's worth
keeping it up or not ;)

On 22 June 2015 at 17:42, Thomas Refis <thomas.refis@gmail.com> wrote:

> 2015-06-22 15:19 GMT+01:00 Gerd Stolpmann <info@gerd-stolpmann.de>:
> > There is one downside of not using ";;", namely that you sometimes get
> > syntax errors much later than necessary. E.g. in
> >
> > let x =
> >   do_this();
> >   do_that();
> > let y = 6
> > let z =
> >   do_third_thing()
> >
> > you get the syntax error at the position of the third "let" although it
> > is the extra semicolon at the end of the first definition. This can be
> > very confusing, and it is a very good reason to use ";;" outside the
> > toplevel. IMHO it is better to be honest about this issue. Because "let"
> > is an open-ended construction the ";;" can be useful as end marker, and
> > the compiler emits better error messages with more precise locations.
>
> The argument seems a bit weak.
> The example is (if I understand correctly): "I have a trailing
> semicolon which the compiler doesn't report properly but instead tells
> me there is a syntax error in a completely unrelated place! If you
> place double semicolons in your code, that doesn't happen!".
> But it could also be understood as: "I usually place double
> semicolons, but in this case I forgot. And the compiler doesn't report
> this properly but instead tells me there is a syntax error in a
> completely unrelated place!".
>
> You face the same problem either way, you still have to be "fluent" to
> know where to look when you encounter this error.
> And I'd guess a beginner is as likely to forget the ";;" as to leave a
> trailing ";".
>
> --
> 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
>

[-- Attachment #2: Type: text/html, Size: 3179 bytes --]