As described in section , some expressions
evaluate ``to themselves'' or to copies of themselves. These
numbers, strings, and characters, and are called
self-evaluating literals. However, some expressions, lists and
symbols in particular, do not evaluate to themselves. When an
expression yielding a particular constant value is required,
it is necessary to use QUOTE. Self-evaluating literals
and quoted constants are called literals.
Although not all objects have external representations, some objects
which do have external representations have undefined evaluation
semantics. These vectors (section ) and the
empty list. QUOTE must also be used to obtain these values as
constants.