17.2.4 Stream input

The following definition for the stream-read-char reads a character from the stream. If the character read is a #\Line-Separator , then the method returns #\Newline , otherwise the character read is returned. It also returns :eof at the end of the file.

(defmethod stream:stream-read-char ((stream unicode-ls-stream))

  (let ((char (read-char (ls-stream-file-stream stream) 

               nil :eof)))

    (if (eq char #\Line-Separator)

        #\Newline

      char)))

There is no need to define a new method for stream-read-line as the default method uses stream-read-char repeatedly to read a line, and our implementation of stream-read-char ensures that this will work.

stream-read-char

Generic Function

Package: stream

The generic function stream-read-char reads one item from stream . The item read is either a character or the end of file symbol :eof if the stream is at the end of a file. Every subclass of fundamental-character-input-stream must define a method for this function.

We also need to make sure that if a #\Newline is unread, it is unread as a #\Line-Separator . The following code uses the Common Lisp file stream function unread-char to achieve this.

(defmethod stream:stream-unread-char ((stream unicode-ls-stream)

                                      char)

  (unread-char (if (eq char #\Newline) #\Line-Separator char)

               (ls-stream-file-stream stream)))

stream-unread-char

Generic Function

Package: stream

The generic function stream-unread-char undoes the last call to stream-read-char , as in unread-char . Every subclass of fundamental-character-input-stream must define a method for this function.

Finally, although the default methods for stream-listen and stream-clear-input would work for our stream, it is faster to use the functions provided by file-stream , using our accessor, ls-stream-file-stream .

(defmethod stream:stream-listen ((stream unicode-ls-stream))

  (listen (ls-stream-file-stream stream)))

(defmethod stream:stream-clear-input ((stream unicode-ls-stream))

  (clear-input (ls-stream-file-stream stream)))

stream-clear-input

Generic Function

Package: stream

The generic function stream-clear-input implements clear-input . The default method is defined on fundamental-input-stream and does nothing.

stream-listen

Generic Function

Package: stream

The generic function stream-listen is used by listen and returns t if there is input available. The default method uses stream-read-char-no-hang and stream-unread-char . Most streams should define their own method as this is usually trivial and more efficient than the method provided.