ANSI Common Lisp 22 Printer 22.3 Formatted Output 22.3.4 FORMAT Printer Operations
220.127.116.11 Tilde W: Write
An argument, any object, is printed obeying every printer control
variable (as by write). In addition, ~W interacts correctly with depth
abbreviation, by not resetting the depth counter to zero. ~W does not
accept parameters. If given the colon modifier, ~W binds *print-pretty*
to true. If given the at-sign modifier, ~W binds *print-level*
and *print-length* to nil.
~W provides automatic support for the detection of circularity and
sharing. If the value of *print-circle* is not nil and ~W is applied
to an argument that is a circular (or shared) reference, an appropriate
#n# marker is inserted in the output instead of printing the argument.