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Re: [Scheme-reports] 6.4 control features: -map and -for-each procedures

Hi John,

On Sat 21 May 2011 23:09, John Cowan <cowan@x> writes:

> Andy Wingo scripsit:
>> Right, control features.  I already mentioned the
>> multiple-return-from-mapping proc issue before.  There are three
>> options that I am aware of:
>>   1) Ignore the issue.
>>   2) Specify that a second return from a mapped procedure cannot
>>   affect the data structure returned by the first return.  Effectively
>>   prohibits the build-it-backwards-and-reverse-in-place idiom, though
>>   you may reverse and form a new list.
>>   3) Specify that it is an error to return multiple times.
> I have filed a ticke for choice 3.  I don't see that anyone will want 2,
> especially for string-map and vector-map.

FWIW R6RS chose option 2, in a discussion in which you participated.
Regarding vector-map:


(Not that long ago, right?)

>> Suggestion: remove vector-map, string-map, and their for-each
>> procedures from the WG1 report.
> The WG1 charter says:  "Self consistency is an important objective,
> which may require adding new features."

I can quote too :)  "A foolish consistency is the hobgoblin of little
minds, adored by little statesmen and philosophers and divines."

Less polemically: consistency has a value, but for me it stops well
before the useless "blob-map".


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