Page 207 Table of Contents Index Page 209
Chapters
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30
A, B, C, D, E


CHAPTER 23. PRESENTATION TYPES

Defines a presentation type whose name is the symbol or class name and whose parameters are
specified by the lambda-list parameters. These parameters are visible within inherit-from and
within the methods created with define-presentation-method. For example, the parameters
are used by presentation-typep and presentation-subtypep methods to refine their tests for
type inclusion.

options is a list of option specifiers. It defaults to nil. An option specifier is either a symbol
or a list (symbol &optional default supplied-p presentation-type accept-options), where symbol,
default, and supplied-p are as in a normal lambda-list. If presentation-type and accept-options
are present, they specify how to accept a new value for this option from the user. symbol can
also be specified in the (keyword variable) form allowed for Common Lisp lambda lists. symbol
is a variable that is visible within inherit-from and within most of the methods created with
define-presentation-method. The keyword corresponding to symbol can be used as an option
in the third form of a presentation type specifier. An option specifier for the standard option
:description is automatically added to options if an option with that keyword is not present,
however it does not produce a visible variable binding.

Unsupplied optional or keyword parameters default to * (as in deftype) if no default is specified
in parameters. Unsupplied options default to nil if no default is specified in options.

inherit-from is a form that evaluates to a presentation type specifier for another type from which
the new type inherits. inherit-from can access the parameter variables bound by the parameters
lambda list and the option variables specified by options. If name is or names a CLOS class
(other than a built-in-class), then inherit-from must specify the class's direct superclasses
(using and to specify multiple inheritance). It is useful to do this when you want to parameterize
previously defined CLOS classes.

If inherit-from is unsupplied, it defaults as follows: If name is or names a CLOS class, then the
type inherits from the presentation type corresponding to the direct superclasses of that CLOS
class (using and to specify multiple inheritance). Otherwise, the type named by name inherits
from standard-object.

description is a string or nil. This should be the term for an instance for the type being de-
fined. If it is nil or unsupplied, a description is automatically generated; it will be a "prettied
up" version of the type name, for example, small-integer would become "small integer".
You can also write a describe-presentation-type presentation method. description is im-
plemented by the default describe-presentation-type method, so description only works in
presentation types where that default method is not shadowed.

history can be t (the default), which means this type has its own history of previous inputs, nil,
which means this type keeps no history, or the name of another presentation type, whose history
is shared by this type. More complex histories can be specified by writing a presentation-
type-history presentation method.

Minor issue: What is a presentation type history? Should they be exposed? | SWM

If the boolean parameters-are-types is true, this means that the parameters to the presentation
type are themselves presentation types. If they are not presentation types, parameters-are-types
should be supplied as false. Types such as and, or, and sequence will specify this as true.

Page 207 Table of Contents Index Page 209
Chapters
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30
A, B, C, D, E