Re: equality types in SML Basis Library (fwd)

Not that this message is off-topic for mlton-user, but it was in
response to a discussion that was started on mlton-devel, and I should
have forwarded the message there.  Follow the link in my quoted e-mail
to see the original discussion.

On Tue, Dec 3, 2013 at 11:24 AM, Matthew Fluet <[email protected]> wrote:
>
> Some thoughts from John Reppy on the equality status of substrings, and
> mono vectors and slices.
>
> ---------- Forwarded message ----------
> Date: Mon, 2 Dec 2013 17:08:50 -0600
> From: John Reppy <[email protected]>
> To: Matthew Fluet <[email protected]>
> Subject: Re: equality types in SML Basis Library
>
> The following is based on memory, but I probably still have the email record somewhere.
>
> For slices, I think that that we decided that they should not be equality types
> because of the potentially surprising behavior of something like
>
>         (Substring.substring("abc", 1, 1) = Substring.substring("xbz", 1, 1))
>
> Substring.compare returns EQUAL on these, but if you call Substring.base, you get unequal
> results, so they are not structurally equal.
>
> For monomorphic vector types, I think that they should all be equality types, except
> for Real vectors (i.e., when their element type is an eqtype).  All array types should
> be equality types (and the "array" type constructor should be treated like "ref").
>
>         - John
>
>
> On Dec 2, 2013, at 2:10 PM, Matthew Fluet <[email protected]> wrote:
>> Hi John,
>>
>> Henry was noticing some inconsistencies between MLton and the SML Basis
>> Library specification with respect to equality status of substrings, and
>> mono vector and vector slices:
>>
>>  http://sourceforge.net/p/mlton/mailman/message/31662605/
>>
>> Any thoughts?  Was it intentional that the monomorphic vectors (other
>> than CharVector) do not have equality status?  Similarly, was it
>> intentional that substrings do not have equality status?
>>
>> -Matthew
>
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