Method: (PRINT-OBJECT FORM T)

Source

(defmethod print-object ((form form) stream)
  (print-unreadable-object (form stream :type t :identity t)
    (when (slot-boundp form 'source)
      (let ((*print-readably* nil)
            (*print-level* 0)
            (*print-length* 4))
        (format stream "~S" (source form))))))