nce of characters that is an expression is also the external
representation of some object.  This can lead to confusion, since it may
not be obvious out of context whether a given sequence of characters is
intended to denote data or program, but it is also a source of power,
since it facilitates writing programs such as interpreters and
compilers that treat programs as data (or vice versa).</p>
<p>
The syntax of external representations of various kinds of objects
accompanies the description of the primitiv