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Multiple Possible Textual Representations

Most objects have more than one possible textual representation. For example, the positive integer with a magnitude of twenty-seven can be textually expressed in any of these ways:

 27    27.    #o33    #x1B    #b11011    #.(* 3 3 3)    81/3

A list containing the two symbols A and B can also be textually expressed in a variety of ways:

 (A B)    (a b)    (  a  b )    (\A |B|) 
(|\A|
  B
)

In general,

from the point of view of the Lisp reader,

wherever whitespace is permissible in a textual representation, any number of spaces and newlines can appear in standard syntax.

When a function such as print produces a printed representation, it must choose from among many possible textual representations. In most cases, it chooses a program readable representation, but in certain cases it might use a more compact notation that is not program-readable.

A number of option variables, called printer control variables , are provided to permit control of individual aspects of the printed representation of objects. Figure 22--1 shows the standardized printer control variables; there might also be implementation-defined printer control variables.

*print-array* *print-gensym* *print-pprint-dispatch* *print-base* *print-length* *print-pretty* *print-case* *print-level* *print-radix* *print-circle* *print-lines* *print-readably* *print-escape* *print-miser-width* *print-right-margin*

Figure 22--1: Standardized Printer Control Variables

In addition to the printer control variables, the following additional defined names relate to or affect the behavior of the Lisp printer:

*package* *read-eval* readtable-case *read-default-float-format* *readtable*

Figure 22--2: Additional Influences on the Lisp printer.


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