Function: WALK-OPTIONAL-ARGUMENT

Source

(defun walk-optional-argument (form parent env)
  (destructuring-bind (name &optional default-value supplied-p-parameter)
      (ensure-list form)
    (with-form-object (arg optional-function-argument-form
                           :parent parent
                           :source form
                           :name name
                           :supplied-p-parameter supplied-p-parameter)
      (setf (default-value arg) (walk-form default-value arg env)))))