Simple objects are sealed, uninstantiable, and concrete. They are often represented by program literals. Figure 11-2 shows the built-in classes of simple objects.
|S||– Sealed||P||– Primary||C||– Concrete||I||– Instantiable|
|O||– Open||F||– Free||A||– Abstract||U||– Uninstantiable|
The class of characters.
The class of characters. All characters are instances of
<character> provides the following operations:
The class of symbols.
<symbol> class provides a built-in, non-case-sensitive dictionary that associates a string with a unique immutable object that can be compared with
== (which should be faster than calling a string-comparison routine). This dictionary is accessed through the
as(<symbol>, string) and
as(<string>, symbol). Any string can be used.
<symbol> provides the following operation:
The class of boolean values.
The class of boolean values. The literal constants
#f are general instances of
<boolean>. Note that for the purposes of conditional expressions, all objects besides
#f count as true. (This does not imply any other objects are instances of