move ABOUT-TO-MODIFY-SYMBOL-VALUE to symbol.lisp

[sbcl.git] / src / code / symbol.lisp

diff --git a/src/code/symbol.lisp b/src/code/symbol.lisp
index 30e629e..6210a6d 100644 (file)
--- a/src/code/symbol.lisp
+++ b/src/code/symbol.lisp
@@ -180,7 +180,7 @@ distinct from the global value. Can also be SETF."
 
 (defun getf (place indicator &optional (default ()))
   #!+sb-doc
-  "Search the property list stored in Place for an indicator EQ to INDICATOR.
+  "Search the property list stored in PLACE for an indicator EQ to INDICATOR.
   If one is found, return the corresponding value, else return DEFAULT."
   (do ((plist place (cddr plist)))
       ((null plist) default)
@@ -246,6 +246,11 @@ distinct from the global value. Can also be SETF."
 \f
 ;;;; GENSYM and friends
 
+(defun %make-symbol-name (prefix counter)
+  (with-output-to-string (s)
+    (write-string prefix s)
+    (%output-integer-in-base counter 10 s)))
+
 (defvar *gensym-counter* 0
   #!+sb-doc
   "counter for generating unique GENSYM symbols")
@@ -272,10 +277,7 @@ distinct from the global value. Can also be SETF."
           (fixnum (values "G" thing))
           (string (values (coerce thing 'simple-string) old)))
       (declare (simple-string prefix))
-      (make-symbol
-       (with-output-to-string (s)
-         (write-string prefix s)
-         (%output-integer-in-base int 10 s))))))
+      (make-symbol (%make-symbol-name prefix int)))))
 
 (defvar *gentemp-counter* 0)
 (declaim (type unsigned-byte *gentemp-counter*))
@@ -284,11 +286,57 @@ distinct from the global value. Can also be SETF."
   #!+sb-doc
   "Creates a new symbol interned in package PACKAGE with the given PREFIX."
   (declare (type string prefix))
-  (loop
-    (let ((*print-base* 10)
-          (*print-radix* nil)
-          (*print-pretty* nil)
-          (new-pname (format nil "~A~D" prefix (incf *gentemp-counter*))))
-      (multiple-value-bind (symbol existsp) (find-symbol new-pname package)
-        (declare (ignore symbol))
-        (unless existsp (return (values (intern new-pname package))))))))
+  (loop for name = (%make-symbol-name prefix (incf *gentemp-counter*))
+        while (nth-value 1 (find-symbol name package))
+        finally (return (values (intern name package)))))
+
+;;; This function is to be called just before a change which would affect the
+;;; symbol value. We don't absolutely have to call this function before such
+;;; changes, since such changes to constants are given as undefined behavior,
+;;; it's nice to do so. To circumvent this you need code like this:
+;;;
+;;;   (defvar foo)
+;;;   (defun set-foo (x) (setq foo x))
+;;;   (defconstant foo 42)
+;;;   (set-foo 13)
+;;;   foo => 13, (constantp 'foo) => t
+;;;
+;;; ...in which case you frankly deserve to lose.
+(defun about-to-modify-symbol-value (symbol action &optional (new-value nil valuep) bind)
+  (declare (symbol symbol))
+  (flet ((describe-action ()
+           (ecase action
+             (set "set SYMBOL-VALUE of ~S")
+             (progv "bind ~S")
+             (compare-and-swap "compare-and-swap SYMBOL-VALUE of ~S")
+             (defconstant "define ~S as a constant")
+             (makunbound "make ~S unbound"))))
+    (let ((kind (info :variable :kind symbol)))
+      (multiple-value-bind (what continue)
+          (cond ((eq :constant kind)
+                 (cond ((eq symbol t)
+                        (values "Veritas aeterna. (can't ~@?)" nil))
+                       ((eq symbol nil)
+                        (values "Nihil ex nihil. (can't ~@?)" nil))
+                       ((keywordp symbol)
+                        (values "Can't ~@?." nil))
+                       (t
+                        (values "Constant modification: attempt to ~@?." t))))
+                ((and bind (eq :global kind))
+                 (values "Can't ~@? (global variable)." nil)))
+        (when what
+          (if continue
+              (cerror "Modify the constant." what (describe-action) symbol)
+              (error what (describe-action) symbol)))
+        (when valuep
+          ;; :VARIABLE :TYPE is in the db only if it is declared, so no need to
+          ;; check.
+          (let ((type (info :variable :type symbol)))
+            (unless (sb!kernel::%%typep new-value type nil)
+              (let ((spec (type-specifier type)))
+                (error 'simple-type-error
+                       :format-control "~@<Cannot ~@? to ~S, not of type ~S.~:@>"
+                       :format-arguments (list (describe-action) symbol new-value spec)
+                       :datum new-value
+                       :expected-type spec))))))))
+  (values))