[Openmcl-devel] non-terminating macro character after Sharpsign Colon
gb at clozure.com
Thu Feb 21 21:29:18 CST 2013
CLHS says (in 18.104.22.168) that #: must be followed by a symbol-name, which
"must have the syntax of a symbol with no package prefix."
A symbol can't begin with a macro character, though a non-terminating macro
character can appear later in a token that has "the syntax of a symbol".
(Of all of the places where the spec uses imprecise language that's
subject to multiple interpretations, this seems ro me to be pretty far
down the list. I don't know whether other implementations that behave
differently do so intentionally or what other reasonable interpretations
would be if so.)
On Fri, 22 Feb 2013, Anton Vodonosov wrote:
> I set $ as a non-terminating macro characters.To smiplify the example,
> let the macro function for that character to be a dummy one:
> (set-macro-character #\$
> (lambda (stream char) :x)
> When $ is a macro character, CCL's reader rejects uninterned symbols
> starting from $, for example #:$, #:$asdf.
> It signals error:
> Reader error: Illegal symbol syntax.
> [Condition of type SIMPLE-ERROR]
> 0: [RETRY] Retry SLIME interactive evaluation request.
> 1: [*ABORT] Return to SLIME's top level.
> 2: [ABORT-BREAK] Reset this thread
> 3: [ABORT] Kill this thread
> 0: (CCL::READ-SYMBOL-TOKEN #<STRING-INPUT-STREAM #x2100D7ECED>)
> 1: (#<Anonymous Function #x1004DA5FF> #<STRING-INPUT-STREAM #x2100D7ECED> #\: NIL)
> 2: (CCL::READ-DISPATCH #<STRING-INPUT-STREAM #x2100D7ECED> #\#)
> 3: (CCL::%PARSE-EXPRESSION #<STRING-INPUT-STREAM #x2100D7ECED> #\# NIL)
> 4: (CCL::%READ-FORM #<STRING-INPUT-STREAM #x2100D7ECED> 0 NIL)
> 5: (CCL::READ-INTERNAL #<STRING-INPUT-STREAM #x2100D7ECED> T NIL NIL)
> 6: (READ #<STRING-INPUT-STREAM #x2100D7ECED> T NIL NIL)
> 7: (READ-FROM-STRING "#:$" T NIL :START 0 :END NIL :PRESERVE-WHITESPACE NIL)
> 8: ((:INTERNAL SWANK::FROM-STRING))
> Why it is so? After all, the macro character is non-terminating, so in the middle
> of the tocken it should have no effect.
> I have tested on other lisps. SBCL and ABCL read #:$ without problems.
> CLISP on the other hand, like CCL can't read #:$.
> Best regards,
> - Anton
> Openmcl-devel mailing list
> Openmcl-devel at clozure.com
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