The following definition for the stream-write-char
uses write-char
to write a character to the stream. If the character written to unicode-ls-stream
is a #\Newline
, then the method writes a #\Line-Separator
to the file stream.
(defmethod stream:stream-write-char ((stream unicode-ls-stream)
char)
(write-char (if (eq char #\Newline)
#\Line-Separator
char)
(ls-stream-file-stream stream)))
stream-write-char stream character
The generic function stream-write-char
writes character to stream . Every subclass of fundamental-character-output-stream
must have a method defined for this function.
The default method for stream-write-string
calls the above generic function and successfully write a string to the stream. However, the following is a more efficient implementation for our stream.
(defmethod stream:stream-write-string ((stream unicode-ls-stream)
string &optional (start 0)
(end (length string)))
(loop with i = start
until (>= i end)
do (let* ((newline (position #\Newline
string :start i :end end))
(this-end (or newline end)))
(write-string string (ls-stream-file-stream stream)
:start i :end this-end)
(incf i this-end)
(when newline
(stream:stream-terpri stream)
(incf i)))
finally (return string)))
We do not need to define our own method for stream-terpri
, as the default uses stream-write-char
, and therefore works appropriately
To be useful, the stream-line-column
and stream-line-start-p
generic functions need to know the number of characters preceding a #\Line-Separator
. However, since the LispWorks file stream records line position only by #\Newline
characters, this information is not available. Hence we define the two generic functions to return nil
:
(defmethod stream:stream-line-column
((stream unicode-ls-stream))
nil)
(defmethod stream:stream-start-line-p
((stream unicode-ls-stream))
nil)
stream-line-column stream
The generic function stream-line-column
returns the column number where the next character will be written from stream , or nil
if this is not meaningful for the stream. This function is used in the implementation of print
and the format ~t
directive. A method for this function must be defined for every character output stream class that is defined, although at its simplest it may be defined to always return nil
.
stream-start-line-p stream
The generic function stream-start-line-p
returns t
if stream is positioned at the beginning of a line, and nil
otherwise. It is permissible to define a method that always returns nil
.
Finally, the methods for stream-force-output
, stream-finish-output
and stream-clear-output
are "trampolined" from the standard force-output
, finish-output
and clear-output
functions.
(defmethod stream:stream-force-output ((stream
unicode-ls-stream))
(force-output (ls-stream-file-stream stream)))
(defmethod stream:stream-finish-output ((stream
unicode-ls-stream))
(finish-output (ls-stream-file-stream stream)))
(defmethod stream:stream-clear-output ((stream
unicode-ls-stream))
(clear-output (ls-stream-file-stream stream)))