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

[Damien Doligez <damien.doligez@inria.fr>]

Gerd has totally nailed it, and that's the reason why I always use ;;
in my code.
If we had another keyword for toplevel let (let without in) the
situation would be quite different.

-- Damien


On Mon, Jun 22, 2015 at 10:19 AM, Gerd Stolpmann <info@gerd-stolpmann.de> wrote:
> Am Montag, den 22.06.2015, 15:31 +0200 schrieb Alan Schmitt:
>> Hello,
>>
>> In my Ocaml class, I tend to promote the use of ";;" to separate phrases
>> (I'm basically following
>> http://ocaml.org/learn/tutorials/structure_of_ocaml_programs.html#Usingandomittingand
>> although I was not aware of this page when I created the course). My
>> motivation is to minimize the difference between using the top-level and
>> writing files.
>>
>> I am now wondering if this is a good practice. In a nutshell, would you
>> rather use
>>
>> #+begin_src ocaml
>> let x = 12;;
>> print_endline "Hello World!"
>> #+end_src
>>
>> or
>>
>> #+begin_src ocaml
>> let x = 12
>> let () = print_endline "Hello World!"
>> #+end_src
>>
>> when teaching Ocaml?
>
> 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.
>
> Gerd
>
>
>
>> Thanks,
>>
>> Alan
>>
>
> --
> ------------------------------------------------------------
> Gerd Stolpmann, Darmstadt, Germany    gerd@gerd-stolpmann.de
> My OCaml site:          http://www.camlcity.org
> Contact details:        http://www.camlcity.org/contact.html
> Company homepage:       http://www.gerd-stolpmann.de
> ------------------------------------------------------------
>