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.