print-object (object standard-object) stream print-object (object structure-object) stream
object—an object.
stream—a stream.
The generic function print-object writes the printed representation of object
to stream.
The function print-object is called by the Lisp printer;
it should not be called by the user.
Each implementation is required to provide a method on
the class standard-object and on the class structure-object.
In addition, each implementation must provide
methods on enough other classes
so as to ensure that there is always an applicable method.
Implementations are free to add methods for other classes.
Users may write methods for print-object for their own
classes if they do not wish to inherit an
implementation-dependent method.
The method on the class structure-object prints the object in the
default #S notation; see Section 22.1.3.12 (Printing Structures).
Methods on print-object are responsible for implementing
their part of the semantics of the printer control variables, as follows:
*print-readably*All methods for print-object must obey *print-readably*.
This includes both user-defined methods and implementation-defined methods.
Readable printing of structures and standard objects
is controlled by their print-object method,
not by their make-load-form method.
Similarity for these objects is application dependent
and hence is defined to be whatever these methods do;
see Section 3.2.4.2 (Similarity of Literal Objects).
*print-escape*Each method must implement *print-escape*.
*print-pretty*The method may wish to perform specialized line breaking
or other output conditional on the value of *print-pretty*.
For further information,
see (for example) the macro pprint-fill.
See also Section 22.2.1.4 (Pretty Print Dispatch Tables) and Section 22.2.2 (Examples of using the Pretty Printer).
*print-length*Methods that produce output of indefinite length must obey
*print-length*.
For further information,
see (for example) the macros pprint-logical-block
and pprint-pop.
See also Section 22.2.1.4 (Pretty Print Dispatch Tables) and Section 22.2.2 (Examples of using the Pretty Printer).
*print-level*The printer takes care of *print-level* automatically,
provided that each method handles exactly one level of structure and
calls write (or an equivalent function) recursively if
there are more structural levels. The printer's decision of whether an
object has components (and therefore should not be printed when the
printing depth is not less than *print-level*) is
implementation-dependent. In some implementations its
print-object method is not called;
in others the method is called,
and the determination that the object has components is based on what
it tries to write to the stream.
*print-circle*When the value of *print-circle* is true,
a user-defined
print-object method
can print objects to the supplied stream
using write,
prin1,
princ,
or format
and expect circularities to be detected
and printed using the #n# syntax.
If a user-defined
print-object method
prints to a stream other than the one
that was supplied, then circularity detection starts over for that
stream. See *print-circle*.
*print-base*, *print-radix*, *print-case*, *print-gensym*, and *print-array*These printer control variables apply to specific types of objects and are handled by the methods for those objects.
If these rules are not obeyed, the results are undefined.
In general, the printer and the print-object methods should not
rebind the print control variables as they operate recursively through the
structure, but this is implementation-dependent.
In some implementations the stream argument passed to a
print-object method is not the original stream,
but is an intermediate stream that implements part of the printer.
methods should therefore not depend on the identity of this stream.
pprint-fill, pprint-logical-block, pprint-pop, write, *print-readably*, *print-escape*, *print-pretty*, *print-length*, Section 22.1.3 (Default Print-Object Methods), Section 22.1.3.12 (Printing Structures), Section 22.2.1.4 (Pretty Print Dispatch Tables), Section 22.2.2 (Examples of using the Pretty Printer)