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Message from discussion portable detection of special symbols?
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RG  
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 More options Apr 24 2011, 3:29 am
Newsgroups: comp.lang.lisp
From: RG <rNOSPA...@flownet.com>
Date: Sun, 24 Apr 2011 00:29:15 -0700
Local: Sun, Apr 24 2011 3:29 am
Subject: Re: portable detection of special symbols?
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In article <87zkngf99q....@kuiper.lan.informatimago.com>,
 "Pascal J. Bourguignon" <p...@informatimago.com> wrote:

> D Herring <dherr...@at.tentpost.dot.com> writes:

> > Special Operator SYMBOL-MACROLET:
> > "symbol-macrolet signals an error if a special declaration names one
> > of the symbols being defined by symbol-macrolet"

> > Is there a better way not requiring the cltl2 environment interface?

> So far, we have:

> (defun specialp (symbol)
>   "Detects whether the symbol has been declared special."
>   (and (symbolp symbol)
>        (cond
>         ((constantp symbol) nil)
>         ((not (eql symbol (macroexpand symbol))) nil)
>         (t (handler-bind ((warning (function muffle-warning)))
>              (eval `(flet ((f () ,symbol))
>                       (let ((,symbol t))
>                         (not (nth-value 1 (ignore-errors (f))))))))))))

> (defvar a 1)
> (defconstant c 2)
> (define-symbol-macro sa a)
> (define-symbol-macro sb b)
> (define-symbol-macro sc c)
> (define-symbol-macro sd d)
> (define-symbol-macro se 42)

> (values
>  (funcall (compile nil (lambda ()
>                            (let ((b 1))
>                              (declare (special b))
>                              (list (specialp 'a)  (specialp 'b)
>                                    (specialp 'c)  (specialp 'd)
>                                    (specialp 'sa) (specialp 'sb)
>                                    (specialp 'sc) (specialp 'sd)
>                                    (specialp 'se))))))
>  (list (specialp 'a)  (specialp 'b)
>        (specialp 'c)  (specialp 'd)
>        (specialp 'sa) (specialp 'sb)
>        (specialp 'sc) (specialp 'sd)
>        (specialp 'se)))

> ;; (T T   NIL NIL NIL NIL NIL NIL NIL)
> ;; (T NIL NIL NIL NIL NIL NIL NIL NIL)

> I claim that SPECIALP is conforming, and any implementation not giving
> the same results on any symbol is not conforming.

Then CCL, CLisp and SBCL are all non-conforming:

Welcome to Clozure Common Lisp Version 1.7-dev-r14715M-trunk  
(DarwinX8664)!
? (defun specialp (symbol)
  "Detects whether the symbol has been declared special."
  (and (symbolp symbol)
       (cond
        ((constantp symbol) nil)
        ((not (eql symbol (macroexpand symbol))) nil)
        (t (handler-bind ((warning (function muffle-warning)))
             (eval `(flet ((f () ,symbol))
                      (let ((,symbol t))
                        (not (nth-value 1 (ignore-errors (f))))))))))))
SPECIALP
? (setf (symbol-value 'x) 1)
1
? (specialp 'x)
T
? (flet ((f () x)) (let ((x 2)) (f)))
;Compiler warnings :
;   In F inside an anonymous lambda form: Undeclared free variable X
;   In an anonymous lambda form at position 17: Unused lexical variable X
1

I won't bother to post the transcripts from CLisp and SBCL, the results
are the same.

rg


 
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