[Openmcl-devel] Error on macro character after sharpsign colon

Terje Norderhaug terje at in-progress.com
Tue Jan 26 20:41:52 UTC 2010


On Jan 26, 2010, at 12:17 PM, Andrew Shalit wrote:
> It's the no-man's land between Canada and Luxembourg, also known as  
> the "Canadian-Luxembourg Zone".  The region has very strict  
> programming rules.

I've heard it's outside Kansas.

> On Jan 26, 2010, at 3:11 PM, Gary Byers wrote:
>
>> What the hell is "CLZ" ?
>>
>>
>> On Tue, 26 Jan 2010, Terje Norderhaug wrote:
>>
>>> Regarding CLZ not allowing a user defined macro character after the
>>> #: of an uninterned symbol:
>>>
>>> On Jan 25, 2010, at 1:56 PM, Gary Byers wrote:
>>>> The spec says:
>>>>
>>>> "A non-terminating macro character is treated as a constituent when
>>>> it appears in the middle of an extended token being accumulated."
>>>>
>>>> (An initial macro character would cause the function associated  
>>>> with
>>>> that character to be called in the standard reader algorithm
>>>> describted
>>>> in section 2.2; a token that begins with an unescaped macro  
>>>> character
>>>> would not have "the syntax of a symbol.")
>>>>
>>>> The spec says that the <<symbol-name>> following #:"must have the
>>>> syntax of a symbol"; I think that I'd rather have the reader  
>>>> complain
>>>> when this is violated than quietly accept invalid/undefined syntax.
>>>
>>> Wouldn't it be reasonable to understand "syntax of a symbol" in the
>>> spec to refer to the Standard Syntax rather than the user extended
>>> syntax? If so, the reader could complain when the symbol name
>>> following #: starts with a character in the Standard Readtable yet
>>> allow custom macro characters in the Current Readtable.
>>>
>>> Not allowing a user defined macro character after the #: of an
>>> uninterned symbol discourages even careful use of custom reader
>>> macros. An alternative resolution could be to signal a *continuable*
>>> error when encountering an uninterned symbol that starts with a  
>>> macro
>>> character, giving the developer the final say.
>>>
>>>> On Mon, 25 Jan 2010, Terje Norderhaug wrote:
>>>>
>>>>> CLZ fails to read an uninterned symbol if the sharpsign colon is
>>>>> followed by a macro character. Is this a bug or correct  
>>>>> behavior? I
>>>>> got no wiser by reading the hyperspec, but presume it's in there
>>>>> somewhere:
>>>>>
>>>>>   http://www.lispworks.com/documentation/lw50/CLHS/Body/02_b.htm
>>>>>
>>>>> Replicate by evaluating the following:
>>>>>
>>>>> (defun symbol-reader (stream char)
>>>>>   (declare (ignore char))
>>>>>   (read stream t nil t))
>>>>>
>>>>> (set-macro-character #\! #'symbol-reader T)
>>>>>
>>>>> '!abc
>>>>> => ABC
>>>>>
>>>>> '#:!abc
>>>>> => Reader error: Illegal symbol syntax.
>>>>>
>>>>> Backtrace leads to #'read-symbol-token in the l1-reader.
>>>>>
>>>>> LispWorks (5.0 Personal) reads '#:!abc without reporting an error.
>>>>> Which implementation is right?
>>>>>
>>>>> -- Terje Norderhaug
>>>>>  terje at in-progress.com
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> Openmcl-devel mailing list
>>>>> Openmcl-devel at clozure.com
>>>>> http://clozure.com/mailman/listinfo/openmcl-devel
>>>>>
>>>>>
>>>
>>> -- Terje Norderhaug
>>>  terje at in-progress.com
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> Openmcl-devel mailing list
>>> Openmcl-devel at clozure.com
>>> http://clozure.com/mailman/listinfo/openmcl-devel
>>>
>>>
>> _______________________________________________
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>> Openmcl-devel at clozure.com
>> http://clozure.com/mailman/listinfo/openmcl-devel
>

-- Terje Norderhaug
   terje at in-progress.com







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