CLHS: Section 22.1.3.12

22.1.3.12 Printing Structures

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 Section 2.4.8.13 (Sharpsign S).

The following X3J13 cleanup issues, not part of the specification, apply to this section:

STRUCTURE-READ-PRINT-SYNTAX:KEYWORDS
DEFSTRUCT-PRINT-FUNCTION-AGAIN:X3J13-MAR-93