All Manuals > CLIM 2.0 User Guide > Appendix D: Common Lisp Streams

D.3 Character Input

A character input stream can be created by defining a class that includes fundamental-character-input-stream and defining methods for the following generic functions.

stream-read-char Generic Function

stream-read-char stream

Summary: Reads one character from stream, and returns either a character object or the symbol :eof if the stream is at end-of-file. There is no default method for this generic function, so every subclass of fundamental-character-input-stream must define a method.

stream-unread-char Generic Function

stream-unread-char stream character

Summary: Undoes the last call to stream-read-char, as in unread-char, and returns nil. There is no default method for this, so every subclass of fundamental- character-input-stream must define a method.

stream-read-char-no-hang Generic Function

stream-read-char-no-hang stream

Summary: Returns either a character, or nil if no input is currently available, or :eof if end-of-file is reached. This is used to implement read-char-no-hang. The default method provided by fundamental-character-input-stream simply calls stream-read-char; this is sufficient for file streams, but interactive streams should define their own method.

stream-peek-char Generic Function

stream-peek-char stream

Summary: Returns either a character or :eof without removing the character from the stream's input buffer. This is used to implement peek-char; this corresponds to peek-type of nil. The default method calls stream-read-char and stream-unread-char.

stream-listen Generic Function

stream-listen stream

Summary: Returns t if there is any input pending on stream; otherwise, it returns nil. This is used by listen. The default method uses stream-read-char-no-hang and stream-unread-char. Most streams should define their own method, as it will usually be trivial and will generally be more efficient than the default method.

stream-read-line Generic Function

stream-read-line stream

Summary: Returns a string as the first value, and t as the second value if the string was terminated by end-of-file instead of the end of a line. This is used by read-line. The default method uses repeated calls to stream-read-char.

stream-clear-input Generic Function

stream-clear-input stream

Summary: Clears any buffered input associated with stream, and returns nil. This is used to implement clear-input. The default method does nothing.


CLIM 2.0 User Guide - 01 Dec 2021 19:39:02