<s>
In	O
the	O
programming	O
language	O
Lisp	B-Language
,	O
the	O
reader	O
or	O
read	O
function	O
is	O
the	O
parser	B-Language
which	O
converts	O
the	O
textual	O
form	O
of	O
Lisp	B-Language
objects	O
to	O
the	O
corresponding	O
internal	O
object	O
structure	O
.	O
</s>
<s>
In	O
the	O
original	O
Lisp	B-Language
,	O
S-expressions	O
consisted	O
only	O
of	O
symbols	O
,	O
integers	O
,	O
and	O
the	O
list	O
constructors	O
(	O
xi	O
...	O
)	O
and	O
(	O
x	O
.	O
</s>
<s>
Later	O
Lisps	B-Language
,	O
culminating	O
in	O
Common	B-Language
Lisp	I-Language
,	O
added	O
literals	O
for	O
floating-point	O
,	O
complex	O
,	O
and	O
rational	O
numbers	O
,	O
strings	O
,	O
and	O
constructors	O
for	O
vectors	O
.	O
</s>
<s>
Unlike	O
most	O
programming	O
languages	O
,	O
Lisp	B-Language
supports	O
parse-time	O
execution	O
of	O
programs	O
,	O
called	O
"	O
read	O
macros	O
"	O
or	O
"	O
reader	O
macros	O
"	O
.	O
</s>
