Function: MAKE-COLLECTOR

Documentation

Create a collector function. A Collector function will collect, into a list, all the values passed to it in the order in which they were passed. If the callector function is called without arguments it returns the current list of values.

Source

(defun make-collector (&optional initial-value)
  "Create a collector function.

A Collector function will collect, into a list, all the values
passed to it in the order in which they were passed. If the
callector function is called without arguments it returns the
current list of values."
  (let ((value initial-value)
        (cdr (last initial-value)))
    (lambda (&rest items)
      (if items
          (progn
            (if value
                (if cdr
                    (setf (cdr cdr) items
                          cdr (last items))
                    (setf cdr (last items)))
                (setf value items
                      cdr (last items)))
            items)
          value))))