Re: [Caml-list] pattern matching and records vs tuples

[Ashish Agarwal <agarwal1975@gmail.com>]

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> let { foo; bar } = x
> bind the variable foo to the x.foo, and bind bar to x.bar
> I'd prefer to have to annotate non-exhaustive records:>    let { foo =
foo; bar = bar } = x
> should only match { foo; bar }, but
>    let { foo = foo; bar =  bar; .. } = x,
> can match records with more labels.

Both of the above are supported in SML, which I've always felt has better
support for record patterns.


On Tue, Apr 14, 2009 at 9:46 PM, Pal-Kristian Engstad <
pal_engstad@naughtydog.com> wrote:

>  Honestly, I'd prefer to have to annotate non-exhaustive records:
>
>     let { foo = foo; bar = bar } = x
>
> should only match { foo; bar }, but
>
>     let { foo = foo; bar =  bar; .. } = x,
>
> can match records with more labels.
>
> PKE.
>
>
> Yaron Minsky wrote:
>
> On Tue, Apr 14, 2009 at 10:12 AM, Yoann Padioleau <padator@wanadoo.fr>wrote:
>
>>
>> So, would it be possible to extend the ocaml compiler with a simple
>> feature that let the programmer tell the compiler when he use
>> an "exhaustive" pattern with record, e.g.
>>
>>  let foo = function
>>  { field1 = v1; field2 = v2; NOTHING_ELSE} ->
>>
>
> I think this is a great idea (and something I've blogged about before, as
> Christophe Troestler points out).  The thing I've never come up with a good
> proposal for is what would be a pleasant syntax to indicate the
> exhaustiveness of the pattern match.  I could imagine something terse like
> this:
>
>    let {! foo = foo; bar = bar; } = x
>
> where the ! indicates that the pattern match should be exhaustive.  Such
> terse notation would sadly be somewhat obscure.
>
> Another thought I've had for making record matches lighter is to do the
> same kind of trick that's done with labeled arguments, i.e., have
>
>    let { foo; bar } = x
>
> bind the variable foo to the x.foo, and bind bar to x.bar.   Similarly, it
> might be nice for:
>
>     let foo = 3 and bar = 3. in { foo;bar }
>
> to be equivalent to
>
>    let foo = 3 and bar = 3. in { foo = foo; bar = bar }
>
> y
>
>
>
> --
> Pål-Kristian Engstad (engstad@naughtydog.com),
> Lead Graphics & Engine Programmer,
> Naughty Dog, Inc., 1601 Cloverfield Blvd, 6000 North,
> Santa Monica, CA 90404, USA. Ph.: (310) 633-9112.
>
> "Emacs would be a far better OS if it was shipped with
>  a halfway-decent text editor." -- Slashdot, Dec 13. 2005.
>
>
>
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