Scieneer Common Lisp 1.3.9 online documentation

ext:stream-write-char-no-hang stream character[Generic Function]

Writes character to the stream if the write will not block and returns the character. Otherwise return nil without waiting. The default method calls ext:stream-write-char which should be fine for a file stream, however unbuffered character output socket streams will probably want to defined a method for this function. When a character is not written the function ext:stream-waiting-file-descriptor may be called to find the file descriptor and directions blocked and when ready the function may be called again to continue the operation.