(gv-setter, gv-synthetic-place, gv-delay-error): New funs/macros

* lisp/emacs-lisp/gv.el (gv-setter): New function.
(gv-invalid-place): New error.
(gv-get): Use them.
(gv-synthetic-place, gv-delay-error): New places.
* lisp/emacs-lisp/cl-generic.el (cl--generic-setf-rewrite): Remove.
(cl-defgeneric, cl-defmethod): Use gv-setter.

1 files changed, 50 insertions, 7 deletions

diff --git a/lisp/emacs-lisp/gv.el b/lisp/emacs-lisp/gv.el
index fae3bcb86f6..e67888cc060 100644
--- a/lisp/emacs-lisp/gv.el
+++ b/lisp/emacs-lisp/gv.el
@@ -74,6 +74,8 @@
 ;; (defvar gv--macro-environment nil
 ;;   "Macro expanders for generalized variables.")
 
+(define-error 'gv-invalid-place "%S is not a valid place expression")
+
 ;;;###autoload
 (defun gv-get (place do)
   "Build the code that applies DO to PLACE.
@@ -84,8 +86,10 @@ and SETTER is a function which returns the code to set PLACE when called
 with a (not necessarily copyable) Elisp expression that returns the value to
 set it to.
 DO must return an Elisp expression."
-  (if (symbolp place)
-      (funcall do place (lambda (v) `(setq ,place ,v)))
+  (cond
+   ((symbolp place) (funcall do place (lambda (v) `(setq ,place ,v))))
+   ((not (consp place)) (signal 'gv-invalid-place (list place)))
+   (t
     (let* ((head (car place))
            (gf (function-get head 'gv-expander 'autoload)))
       (if gf (apply gf do (cdr place))
@@ -104,8 +108,19 @@ DO must return an Elisp expression."
           (if (eq me place)
               (if (and (symbolp head) (get head 'setf-method))
                   (error "Incompatible place needs recompilation: %S" head)
-                (error "%S is not a valid place expression" place))
-            (gv-get me do)))))))
+                (let* ((setter (gv-setter head)))
+                  (gv--defsetter head (lambda (&rest args) `(,setter ,@args))
+                                 do (cdr place))))
+            (gv-get me do))))))))
+
+(defun gv-setter (name)
+  ;; The name taken from Scheme's SRFI-17.  Actually, for SRFI-17, the argument
+  ;; could/should be a function value rather than a symbol.
+  "Return the symbol where the (setf NAME) function should be placed."
+  (if (get name 'gv-expander)
+      (error "gv-expander conflicts with (setf %S)" name))
+  ;; FIXME: This is wrong if `name' is uninterned (or interned elsewhere).
+  (intern (format "(setf %s)" name)))
 
 ;;;###autoload
 (defmacro gv-letplace (vars place &rest body)
@@ -158,8 +173,10 @@ arguments as NAME.  DO is a function as defined in `gv-get'."
 
 ;;;###autoload
 (or (assq 'gv-expander defun-declarations-alist)
-    (push `(gv-expander ,(apply-partially #'gv--defun-declaration 'gv-expander))
-	  defun-declarations-alist))
+    (let ((x `(gv-expander
+               ,(apply-partially #'gv--defun-declaration 'gv-expander))))
+      (push x macro-declarations-alist)
+      (push x defun-declarations-alist)))
 ;;;###autoload
 (or (assq 'gv-setter defun-declarations-alist)
     (push `(gv-setter ,(apply-partially #'gv--defun-declaration 'gv-setter))
@@ -282,9 +299,9 @@ The return value is the last VAL in the list.
 ;; containing a non-trivial `push' even before gv.el was loaded.
 ;;;###autoload
 (put 'gv-place 'edebug-form-spec 'edebug-match-form)
+
 ;; CL did the equivalent of:
 ;;(gv-define-macroexpand edebug-after (lambda (before index place) place))
-
 (put 'edebug-after 'gv-expander
      (lambda (do before index place)
        (gv-letplace (getter setter) place
@@ -460,6 +477,32 @@ The return value is the last VAL in the list.
              (funcall do `(funcall (car ,gv))
                       (lambda (v) `(funcall (cdr ,gv) ,v))))))))
 
+(defmacro gv-synthetic-place (getter setter)
+  "Special place described by its setter and getter.
+GETTER and SETTER (typically obtained via `gv-letplace') get and
+set that place.  I.e. This macro allows you to do the \"reverse\" of what
+`gv-letplace' does.
+This macro only makes sense when used in a place."
+  (declare (gv-expander funcall))
+  (ignore setter)
+  getter)
+
+(defmacro gv-delay-error (place)
+  "Special place which delays the `gv-invalid-place' error to run-time.
+It behaves just like PLACE except that in case PLACE is not a valid place,
+the `gv-invalid-place' error will only be signaled at run-time when (and if)
+we try to use the setter.
+This macro only makes sense when used in a place."
+  (declare
+   (gv-expander
+    (lambda (do)
+      (condition-case err
+          (gv-get place do)
+        (gv-invalid-place
+         ;; Delay the error until we try to use the setter.
+         (funcall do place (lambda (_) `(signal ',(car err) ',(cdr err)))))))))
+  place)
+
 ;;; Even more debatable extensions.
 
 (put 'cons 'gv-expander