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Re: A value for "nothing"
From: |
Mark H Weaver |
Subject: |
Re: A value for "nothing" |
Date: |
Tue, 28 Aug 2018 11:59:40 -0400 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) |
Mark H Weaver <address@hidden> writes:
> John Cowan <address@hidden> writes:
>
>> On Tue, Aug 28, 2018 at 3:01 AM Mark H Weaver <address@hidden> wrote:
>>
>> In RnRS, (define a (if #f #f)) is allowed and guaranteed to assign
>> *some* object to 'a' without signalling an error.
>>
>> Actually, the phrase used is "the result is unspecified", which unfortunately
>> is not defined in any RnRS.
>
> That's the phrase used in R7RS-small, which fails to define it, as you
> noted, but that shortcoming is limited to R7RS.
Actually, the behavior _is_ clearly defined, in the formal denotational
semantics in both R5RS and R7RS. If you learn how to read those, you'll
see that there's no question that (if #f #f) is guaranteed to return
exactly one unspecified value.
Mark
- Re: A value for "nothing", (continued)
- Re: A value for "nothing", Mark H Weaver, 2018/08/26
- Re: A value for "nothing", Matt Wette, 2018/08/26
- Re: A value for "nothing", tomas, 2018/08/27
- Re: A value for "nothing", Mark H Weaver, 2018/08/27
- Re: A value for "nothing", Hans Åberg, 2018/08/27
- Re: A value for "nothing", Mark H Weaver, 2018/08/27
- Re: A value for "nothing", Matt Wette, 2018/08/27
- Re: A value for "nothing", Mark H Weaver, 2018/08/28
- Re: A value for "nothing", John Cowan, 2018/08/28
- Re: A value for "nothing", Mark H Weaver, 2018/08/28
- Re: A value for "nothing",
Mark H Weaver <=
- Re: A value for "nothing", John Cowan, 2018/08/28
- Re: A value for "nothing", Mark H Weaver, 2018/08/28
- Re: A value for "nothing", Mark H Weaver, 2018/08/28
Re: A value for "nothing", Panicz Maciej Godek, 2018/08/26
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