From: Goswin von Brederlow <goswin-v-b@web.de>
To: Jeremy Yallop <yallop@gmail.com>
Cc: "Daniel Bünzli" <daniel.buenzli@erratique.ch>,
"caml list" <caml-list@inria.fr>
Subject: Re: [Caml-list] Stability of order between polymorphic variants
Date: Thu, 5 Sep 2013 16:46:26 +0200 [thread overview]
Message-ID: <20130905144626.GA31556@frosties> (raw)
In-Reply-To: <CAAxsn=FV00_ky3Zfd8yN9H01fe2wPs5MVpmrPtsyK6M4YYmuQQ@mail.gmail.com>
On Thu, Sep 05, 2013 at 10:26:42AM +0100, Jeremy Yallop wrote:
> On 5 September 2013 01:17, Daniel Bünzli <daniel.buenzli@erratique.ch> wrote:
> > The question is, is the order between polymorphic variants an invariant provided by the compiler or is it subject to change ?
>
> The order is fairly unlikely to change. It's based on a hash function
> that's used during type checking to determine whether tags can occur
> in the same type:
>
> # [`premiums; `squigglier];;
> Characters 12-23:
> [`premiums; `squigglier];;
> ^^^^^^^^^^^
> Error: Variant tags `premiums and `squigglier have the same hash value.
> Change one of them.
>
> Changing the hash function could cause some existing programs to be rejected.
Wow, those names even look sensible. Nice collision example.
MfG
Goswin
prev parent reply other threads:[~2013-09-05 14:46 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-05 0:17 Daniel Bünzli
2013-09-05 2:06 ` Anthony Tavener
2013-09-05 2:11 ` Anthony Tavener
2013-09-05 2:18 ` Francois Berenger
2013-09-05 2:31 ` Anthony Tavener
2013-09-05 7:47 ` Stéphane Glondu
2013-09-05 8:24 ` Jacques Garrigue
2013-09-05 8:39 ` Mark Shinwell
2013-09-05 9:26 ` Jeremy Yallop
2013-09-05 14:46 ` Goswin von Brederlow [this message]
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