input-stream-p

(input-stream-p stream)

t when the stream can be read from. A string input stream, a file stream opened :input or :io, a socket and the standard input stream answer t; a string output stream, a file stream opened for output only and a file stream that has been closed answer nil. A synonym stream answers for the stream it currently forwards to. The designator t answers t for both directions, and anything that is not a stream answers nil. A Gray stream instance answers t when its class descends from rontolisp:fundamental-input-stream.