Land of Lisp

Control Sequences for Printing Lisp Values

Any Lisp value can be printed with the print or prin1 command. To print a value for humans, without any delimiters, we can use the princ command:

> (prin1 "foo")
"foo"
> (princ "foo")
foo

We can use the ˜s and ˜a control sequences with format to produce the same behavior as prin1 and princ. When used with format, the ˜s control sequence includes appropriate delimiters. The ˜a shows the value, without delimiters, for humans to read:

> (format t "I am printing ˜s in the middle of this sentence." "foo")
I am printing "foo" in the middle of this sentence.
> (format t "I am printing ˜a in the middle of this sentence." "foo")
I am printing foo in the middle of this sentence.

We can adjust the behavior of these ...