22.3.1.1 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-\partial (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.

~@C binds *print-escape* to t.