These generic functions must be defined for all stream classes.
stream-element-type [Generic Function]
Summary: This existing Common Lisp function is made generic, but otherwise behaves the same. Class fundamental-character-stream provides a default method that returns character .
open-stream-p [Generic Function]
Summary: This function is made generic. A default method is provided by class fundamental-stream that returns t if close has not been called on the stream.
close [Generic Function]
Summary: The existing Common Lisp function close is redefined to be a generic function, but otherwise it behaves the same. The default method provided by the class fundamental-stream sets a flag used by open-stream-p . The value returned by close will be as specified by the X3J13 issue closed-stream-operations .
stream-pathname [Generic Function]
stream-truename [Generic Function]
Summary: These are used to implement pathname and truename . There is no default method because these are not valid for all streams.
Common Lisp Interface Manager 2.0 User's Guide - 7 Aug 2017