By default, a structure of type S is printed using #S syntax.
This behavior can be customized by specifying a :print-function
or :print-object option to the defstruct form that defines S,
or by writing a print-object method
that is specialized for objects of type S.
Different structures might print out in different ways; the default notation for structures is:
#S(structure-name {slot-key slot-value}*)
where #S indicates structure syntax,
structure-name is a structure name,
each slot-key is an initialization argument name
for a slot in the structure,
and each corresponding slot-value is a representation
of the object in that slot.
For information on how the Lisp reader parses structures, see Sharpsign S.