anchor.diff:  (define-binder (nil var (val (eql nil)) decls body)
     (let ((decl (use-declaration var decls)))
       `(let (,var)
  -       ,@(when decl `((declare ,@decl)))
  -       ,@body)))
  -
  -(define-binder (nil (var list) val decls body)
  -  (multiple-value-bind (vars decl)
  -      (process-lambda-list-with-ignore-markers var decls '_)
  -    `(destructuring-bind ,vars ,val
          ,@(when decl `((declare ,@decl)))
          ,@body)))
   
  
positive.code: (defun valid-varname-p (symbol)
    (and (symbolp symbol) (not (keywordp symbol))))
  
  (defmacro when-let ((var test) &body body)
    `(let ((,var ,test))
       (when ,var
  
negative.code:                  :from-end t
                   :initial-value body))))
  
  (flet ((expand-bindings-form (bindings body decls)
           (reduce (lambda (binding body)
                     (destructuring-bind (var-form . val) binding
                       (multiple-value-bind (spec var)
                           (parse-binding `(,var-form ,val))
                         (list (expand-binding spec var val decls body)))))
                   bindings
                   :from-end t
                   :initial-value body)))
          
    (define-binder (nil (var list) val decls body)
      (multiple-value-bind (vars bindings)
          (extract-nested-binding-specs var decls)
        `(destructuring-bind ,vars ,val
           ,@(when-let (decl (mapcan (lambda (x) (use-declaration x decls)) vars))
                       `((declare ,@decl)))
           ,@(expand-bindings-form bindings body decls))))
  
    (define-binder (:mval (var list) val decls body)
      (multiple-value-bind (vars bindings)
          (extract-nested-binding-specs var decls)
        `(multiple-value-bind ,vars ,val
           ,@(when-let (decl (mapcan (lambda (x) (use-declaration x decls)) vars))
                       `((declare ,@decl)))
           ,@(expand-bindings-form bindings body decls)))))
  
  (define-binder (:slot (var list) val decls body)
    (let ((decl (mapcan (lambda (x) (use-declaration x decls))
  