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Common Lisp like feature expressions (was: How and when to use GCPRO?)
From: |
Leo |
Subject: |
Common Lisp like feature expressions (was: How and when to use GCPRO?) |
Date: |
Mon, 27 Dec 2010 19:26:03 +0000 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/23.2.91 (Mac OS X 10.6.5) |
On 2010-12-27 16:00 +0000, Stefan Monnier wrote:
> Stefan "wondering why eval_feature_expression would need to be
> written in C rather than in Elisp"
I hadn't thought of that :(
I put together a small patch for anyone who would like to try it:
diff --git a/lisp/subr.el b/lisp/subr.el
index 03f7e04..92f3b0a 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -1719,6 +1719,31 @@ FILE should be the name of a library, with no directory
name."
(eval-after-load file (read)))
(make-obsolete 'eval-next-after-load `eval-after-load "23.2")
+(defun eval-feature-expression (form)
+ (cond
+ ((atom form) (featurep form nil))
+ ;; ensure form is a proper list
+ ((condition-case nil
+ (and (length form) nil)
+ (error (error "Invalid feature expression: %s" form))))
+ ((eq (car form) 'not)
+ (if (= (length form) 2)
+ (not (eval-feature-expression (cadr form)))
+ (error "Invalid feature expression: %s" form)))
+ ((= (length form) 2)
+ (eval-feature-expression (cadr form)))
+ ((eq (car form) 'and)
+ (if (= (length form) 1)
+ t
+ (and (eval-feature-expression (cadr form))
+ (eval-feature-expression (cons 'and (cddr form))))))
+ ((eq (car form) 'or)
+ (if (= (length form) 1)
+ nil
+ (or (eval-feature-expression (cadr form))
+ (eval-feature-expression (cons 'or (cddr form))))))
+ (t (error "Invalid feature expression: %s" form))))
+
;;;; Process stuff.
(defun process-lines (program &rest args)
diff --git a/src/lread.c b/src/lread.c
index 72c01ed..32c36ee 100644
--- a/src/lread.c
+++ b/src/lread.c
@@ -96,6 +96,9 @@ Lisp_Object Qinhibit_file_name_operation;
Lisp_Object Qeval_buffer_list, Veval_buffer_list;
Lisp_Object Qfile_truename, Qdo_after_load_evaluation; /* ACM 2006/5/16 */
+/* Used in feature expression */
+Lisp_Object Qobarray, Qeval_feature_expression;
+
/* Used instead of Qget_file_char while loading *.elc files compiled
by Emacs 21 or older. */
static Lisp_Object Qget_emacs_mule_file_char;
@@ -2426,6 +2429,24 @@ read1 (readcharfun, pch, first_in_list)
UNREAD (c);
invalid_syntax ("#", 1);
}
+ /* feature expressions as in Common Lisp */
+ if (c == '+' || c == '-')
+ {
+ Lisp_Object fexp = read0(readcharfun);
+ fexp = call1 (Qeval_feature_expression, fexp);
+ if (c == '-')
+ fexp = NILP (fexp) ? Qt : Qnil;
+ if (NILP (fexp))
+ {
+ int count = SPECPDL_INDEX ();
+ Lisp_Object tem = Fmake_vector (make_number(17),make_number(0));
+ /* use a temporary obarray */
+ specbind (Qobarray, tem);
+ read0 (readcharfun);
+ unbind_to (count, Qnil);
+ }
+ goto retry;
+ }
if (c == '^')
{
c = READCHAR;
@@ -4536,6 +4557,11 @@ to load. See also `load-dangerous-libraries'. */);
Qcomma_dot = intern_c_string (",.");
staticpro (&Qcomma_dot);
+ Qeval_feature_expression = intern_c_string ("eval-feature-expression");
+ staticpro (&Qeval_feature_expression);
+ Qobarray = intern_c_string ("obarray");
+ staticpro(&Qobarray);
+
Qinhibit_file_name_operation = intern_c_string
("inhibit-file-name-operation");
staticpro (&Qinhibit_file_name_operation);
- Re: How and when to use GCPRO?, (continued)
- Re: How and when to use GCPRO?, Stefan Monnier, 2010/12/27
- Re: How and when to use GCPRO?, Andreas Schwab, 2010/12/27
- Re: How and when to use GCPRO?, Stefan Monnier, 2010/12/27
- Re: How and when to use GCPRO?, Daniel Colascione, 2010/12/27
- Re: How and when to use GCPRO?, Stefan Monnier, 2010/12/27
- Re: How and when to use GCPRO?, Daniel Colascione, 2010/12/27
- Re: How and when to use GCPRO?, Stefan Monnier, 2010/12/27
- Conservative scanning (was: Re: How and when to use GCPRO?), Daniel Colascione, 2010/12/27
- Re: How and when to use GCPRO?, Richard Stallman, 2010/12/28
- Re: How and when to use GCPRO?, Leo, 2010/12/27
- Common Lisp like feature expressions (was: How and when to use GCPRO?),
Leo <=
- Re: Common Lisp like feature expressions (was: How and when to use GCPRO?), Andreas Schwab, 2010/12/27
- Re: Common Lisp like feature expressions (was: How and when to use GCPRO?), Leo, 2010/12/27
- Re: Common Lisp like feature expressions, Stefan Monnier, 2010/12/27
- Re: Common Lisp like feature expressions, Leo, 2010/12/28