Question about O'Caml 3

Question about O'Caml 3

[Thorsten Ohl]

Contrary to the documentation, O'Caml 3.00 accepts, lowercase
identifiers for polymorphic variants.

ohl@heplix4:~Mail$ ocaml
        Objective Caml version 3.00

# `foo;;
- : [> `foo] = `foo

Who's right: the compiler or the manual?

BTW: the new syntax for labels is very readable.  Congratulations.
 
Cheers,
-Thorsten
-- 
Thorsten Ohl, Physics Department, TU Darmstadt -- ohl@hep.tu-darmstadt.de
http://heplix.ikp.physik.tu-darmstadt.de/~ohl/ [<=== PGP public key here]

Re: Question about O'Caml 3

[Jacques Garrigue]

From: Thorsten Ohl <ohl@hep.tu-darmstadt.de>

> Contrary to the documentation, O'Caml 3.00 accepts, lowercase
> identifiers for polymorphic variants.
> 
> ohl@heplix4:~Mail$ ocaml
>         Objective Caml version 3.00
> 
> # `foo;;
> - : [> `foo] = `foo
> 
> Who's right: the compiler or the manual?

Well, we were so busy discussing label syntax that this point was not
debated before 3.00.
The current answer is: both are correct.

If you want to be on the safe side, better not to use lowercase
variants, since they could be removed in the future.
Also they are probably not so nice if you are really intending to use
them as sum types, which are usually identified by their uppecase
first letter.
On the other hand, I have a personal liking for lowercase variants, at
least when they have only an abstract meaning (not really used as
values, but rather as types, and types are lowercase).

Some libraries, namely lablGL and lablGTK (only internally for
lalblGTK), actually use lowercase labels, so I prefered to keep them
for now in the compiler, as they are not harmful, rather than having
to correct everything before a real decision is taken.

---------------------------------------------------------------------------
Jacques Garrigue      Kyoto University     garrigue at kurims.kyoto-u.ac.jp
		<A HREF=http://wwwfun.kurims.kyoto-u.ac.jp/~garrigue/>JG</A>

Re: Question about O'Caml 3

[Thorsten Ohl]

Jacques Garrigue <garrigue@kurims.kyoto-u.ac.jp> writes:

> If you want to be on the safe side, better not to use lowercase
> variants, since they could be removed in the future.  Also they are
> probably not so nice if you are really intending to use them as sum
> types, which are usually identified by their uppecase first letter.
> On the other hand, I have a personal liking for lowercase variants,
> at least when they have only an abstract meaning (not really used as
> values, but rather as types, and types are lowercase).

When ocaml-2.99 came out I tried to pick up idioms with polymorphic
variants from the lablgtk sources and I was very confused by this
ambiguity.

As you said, the lowercase polymorphic variants appeared to be used
more like types and the uppercase polymorphic variants appeared to be
usd more like sum types.  However, the lowercase polymorphic variants
were not mentioned anywhere ... 

>From the compiler sources, I then found out that there is no
difference and assumed (apparently correctly) that they are there for
olabl compatibility.

I'm not complaining about lack of documentation, but I want to point
out that such ambiguities make it hard for novices (it's my fault,
that I hadn't studied olabl before, of course) to pick up proper
idioms in a programming language.

Cheers,
-Thorsten
-- 
Thorsten Ohl, Physics Department, TU Darmstadt -- ohl@hep.tu-darmstadt.de
http://heplix.ikp.physik.tu-darmstadt.de/~ohl/ [<=== PGP public key here]

O'Caml 3 doco

[John Max Skaller]

There's another glitch in the ocaml 3.00 documentation:
it says that 'of' is elided in polymorphic variants.
This was the case in 2.99 but has been changed in 3.00.

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