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

[Thomas Refis <thomas.refis@gmail.com>]

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 ";".