[Sbcl-devel] get-macro-character broken?

[Daniel B. <da...@te...>]

CLHS says 

  "get-macro-character returns as its primary value, function, the
  reader macro function associated with char in readtable (if any), or
  else nil if char is not a macro character in readtable."

Yet SBCL says, using standard syntax

* (get-macro-character #\Space *readtable*)

#<FUNCTION "top level local call SB!IMPL::UNDEFINED-MACRO-CHAR" {10665CD}>
T

2.1.4 says #\Space was the "whitespace" syntax type, not a macro
character - terminating or otherwise.  I don't know if there's some
interpretation of the standard that makes this behaviour allowable,
but I do know it's somewhat surprising, because set-macro-character
(correctly) changes the syntax type.

The appended code is ugly, I concede, but I found it in the wild (in
SLIME, in fact) and I don't see any other way to do it.  Ideas?


(defun make-source-recording-readtable (readtable source-map) 
  "Return a source position recording copy of READTABLE.
The source locations are stored in SOURCE-MAP."
  (let* ((tab (copy-readtable readtable))
	 (*readtable* tab)
	 (undefined-macro (get-macro-character #\Space tab)))
    ;; not sure why this should be the case, but SBCL returns
    ;; #<FUNCTION "top level local call SB!IMPL::UNDEFINED-MACRO-CHAR">
    ;; for (get-macro-character) on characters that aren't macros.
    (dotimes (code char-code-limit)
      (let ((char (code-char code)))
	(multiple-value-bind (fn term) (get-macro-character char tab)
	  (when (and fn (not (eq fn undefined-macro)))
	    (set-macro-character char (make-source-recorder fn source-map) 
				 term tab)))))
    tab))


-dan

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