[Openmcl-devel] Error on macro character after sharpsign colon
ron at flownet.com
Tue Jan 26 11:58:56 PST 2010
Just out of curiosity, why would anyone ever want to read an uninterned symbol whose name began with a macro character?
On Jan 26, 2010, at 11:38 AM, 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
>> 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
>>> 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
>>> => 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
> -- Terje Norderhaug
> terje at in-progress.com
> Openmcl-devel mailing list
> Openmcl-devel at clozure.com
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