From: Luc Maranget <Luc.Maranget@inria.fr>
To: Jon Harrop <postmaster@jdh30.plus.com>
Cc: caml-list <caml-list@inria.fr>
Subject: Re: [Caml-list] Pattern matching over elements at the front of a container
Date: Mon, 28 Jun 2004 09:57:09 +0200 [thread overview]
Message-ID: <20040628095709.B17827@beaune.inria.fr> (raw)
In-Reply-To: <200406261215.26971.postmaster@jdh30.plus.com>; from postmaster@jdh30.plus.com on Sat, Jun 26, 2004 at 12:15:26PM +0100
Hello,
>
> I'm currently storing stuff and things in a list. The ability to pattern match
> over the first element or two using a succinct notation is, of course, nifty.
> However, I'd like to replace my list with some other container, maybe an
> array, maybe something of my own creation. What's the easiest way to keep my
> ability to pattern match over the first few elements at the front of the
> container? I could try to extract the first couple of elements and match over
> a 2-tuple of "element option"s. Can a lazily evaluated stream help? How
> expensive is this in terms of performance?
Well, have a try, you may pay a little in performance, most of the time it
does not matter.
>
> In the case of lists, you can match against the first two elements using the
> pattern "a::b::_". As the "_" is not bound in the corresponding expression,
> an equivalent notation could be invented for arrays in this case. Is this
> feasible? Would anyone else find this useful?
It is certainly feasible, whether it is worth including in the compiler is debatable...
>
> Also, is it not possible to alter the definition and implementation of OCaml
> such that the pattern "(a, a)" is treated as "(a, b) when a=b"? Has this not
> been done because the "=" is suspect?
Just say No (to non-linear patterns) !
Basically and you can interpret this by saying << = is suspect >>, this apparently innocent
addition is a radical change in semantics.
>
> Cheers,
> Jon.
>
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--
Luc Maranget
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next prev parent reply other threads:[~2004-06-28 7:57 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-06-26 11:15 Jon Harrop
2004-06-26 13:36 ` skaller
2004-06-27 10:11 ` Richard Jones
2004-06-27 11:40 ` William Lovas
2004-06-28 7:57 ` Luc Maranget [this message]
2004-06-28 12:01 ` Jon Harrop
2004-06-28 12:50 ` Luc Maranget
2004-06-28 17:09 ` Jon Harrop
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