ssetf

[ghost]

Often, I want to refer to the place I'm setting with an anaphora. The code to do this is as follows:

(defmacro ssetf (&rest bindings)
  "Anaphoric setf that binds it to a symbol-macro evaluating to name."
  `(progn
     ,@(loop for (name val &rest _) on bindings by #'cddr
             collect
             `(symbol-macrolet ((it ,name))
                (setf it ,val)))))

[tokenrove]

My initial thought is that most uses of this would probably be better done with a modify macro. Is there a compelling example for ssetf?

[noctuid]

This article has some good examples (I think) of a somewhat similar macro called zapf (modified to use it):

(defmacro zapf (place expr)
  (multiple-value-bind
        (temps exprs stores store-expr access-expr)
      (get-setf-expansion place)
    `(let* (,@(mapcar #'list temps exprs)
            (,(car stores)
              (let ((it ,access-expr))
                ,expr)))
       ,store-expr)))

(defun move-ball (ball distance screen-width)
  (zapf (ball-x ball)
        (mod (+ distance it) screen-width)))