Format Function

(format <stream> <fmt> <arg>...)  DO FORMATTED OUTPUT
    <stream>    the output stream
    <fmt>       the format string
    <arg>       the format arguments
    returns     output string if <stream> is nil, nil otherwise

The format string can contain characters that should be copied directly to the output and formatting directives. The formatting directives are:

    ~A          print next argument using princ
    ~S          print next argument using prin1
    ~%          start a new line
    ~~          print a tilde character