ANSI Common Lisp 22 Printer 22.3 Formatted Output 22.3.1 FORMAT Basic Output
220.127.116.11 Tilde C: Character
The next arg should be a character; it is printed according to the modifier flags.
~C prints the character as if by using write-char if it is a simple character. Characters that are not simple are not necessarily printed as if by write-char, but are displayed in an implementation-defined, abbreviated format. For example,
(format nil "~C" #\A) "A" (format nil "~C" #\Space) " "
~:C is the same as ~C for printing characters, but other characters are "spelled out." The intent is that this is a "pretty" format for printing characters. For simple characters that are not printing, what is spelled out is the name of the character (see char-name). For characters that are not simple and not printing, what is spelled out is implementation-defined. For example,
(format nil "~:C" #\A) "A" (format nil "~:C" #\Space) "Space" ;; This next example assumes an implementation-defined "Control" attribute. (format nil "~:C" #\Control-Space) "Control-Space" OR"c-Space"
~:@C prints what ~:C would, and then if the character requires unusual shift keys on the keyboard to type it, this fact is mentioned. For example,
(format nil "~:@C" #\Control-Partial) "Control- (Top-F)"
This is the format used for telling the user about a key he is expected to type, in prompts, for instance. The precise output may depend not only on the implementation, but on the particular I/O devices in use.
~@C prints the character in a way that the Lisp reader can understand, using #\ syntax.