<s>
Common	B-Language
Lisp	I-Language
(	O
CL	O
)	O
is	O
a	O
dialect	O
of	O
the	O
Lisp	B-Language
programming	I-Language
language	I-Language
,	O
published	O
in	O
ANSI	O
standard	O
document	O
ANSI	O
INCITS	O
226-1994	O
(	O
S20018	O
)	O
(	O
formerly	O
X3.226-1994	O
(	O
R1999	O
)	O
)	O
.	O
</s>
<s>
The	O
Common	B-Language
Lisp	I-Language
HyperSpec	I-Language
,	O
a	O
hyperlinked	O
HTML	B-Language
version	O
,	O
has	O
been	O
derived	O
from	O
the	O
ANSI	B-Language
Common	I-Language
Lisp	I-Language
standard	I-Language
.	O
</s>
<s>
The	O
Common	B-Language
Lisp	I-Language
language	I-Language
was	O
developed	O
as	O
a	O
standardized	O
and	O
improved	O
successor	O
of	O
Maclisp	B-Language
.	O
</s>
<s>
By	O
the	O
early	O
1980s	O
several	O
groups	O
were	O
already	O
at	O
work	O
on	O
diverse	O
successors	O
to	O
MacLisp	B-Language
:	O
Lisp	B-Language
Machine	I-Language
Lisp	I-Language
(	O
aka	O
ZetaLisp	B-Language
)	O
,	O
Spice	B-Language
Lisp	I-Language
,	O
NIL	B-Language
and	O
S-1	B-Language
Lisp	I-Language
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
sought	O
to	O
unify	O
,	O
standardise	O
,	O
and	O
extend	O
the	O
features	O
of	O
these	O
MacLisp	B-Language
dialects	O
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
is	O
not	O
an	O
implementation	O
,	O
but	O
rather	O
a	O
language	O
specification	B-Application
.	O
</s>
<s>
Several	O
implementations	O
of	O
the	O
Common	B-Language
Lisp	I-Language
standard	O
are	O
available	O
,	O
including	O
free	B-License
and	I-License
open-source	I-License
software	I-License
and	O
proprietary	O
products	O
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
is	O
a	O
general-purpose	O
,	O
multi-paradigm	O
programming	O
language	O
.	O
</s>
<s>
It	O
supports	O
a	O
combination	O
of	O
procedural	B-Application
,	O
functional	B-Language
,	O
and	O
object-oriented	B-Language
programming	I-Language
paradigms	O
.	O
</s>
<s>
As	O
a	O
dynamic	B-Language
programming	I-Language
language	I-Language
,	O
it	O
facilitates	O
evolutionary	O
and	O
incremental	O
software	O
development	O
,	O
with	O
iterative	O
compilation	B-Language
into	O
efficient	O
run-time	O
programs	O
.	O
</s>
<s>
It	O
also	O
supports	O
optional	O
type	O
annotation	O
and	O
casting	O
,	O
which	O
can	O
be	O
added	O
as	O
necessary	O
at	O
the	O
later	O
profiling	O
and	O
optimization	O
stages	O
,	O
to	O
permit	O
the	O
compiler	B-Language
to	O
generate	O
more	O
efficient	O
code	O
.	O
</s>
<s>
For	O
instance	O
,	O
fixnum	O
can	O
hold	O
an	O
unboxed	O
integer	O
in	O
a	O
range	O
supported	O
by	O
the	O
hardware	O
and	O
implementation	O
,	O
permitting	O
more	O
efficient	O
arithmetic	O
than	O
on	O
big	O
integers	O
or	O
arbitrary	B-Algorithm
precision	I-Algorithm
types	O
.	O
</s>
<s>
Similarly	O
,	O
the	O
compiler	B-Language
can	O
be	O
told	O
on	O
a	O
per-module	O
or	O
per-function	O
basis	O
which	O
type	O
of	O
safety	O
level	O
is	O
wanted	O
,	O
using	O
optimize	O
declarations	O
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
includes	O
CLOS	B-Application
,	O
an	O
object	B-Language
system	I-Language
that	O
supports	O
multimethods	O
and	O
method	O
combinations	O
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
is	O
extensible	O
through	O
standard	O
features	O
such	O
as	O
Lisp	B-Language
macros	O
(	O
code	O
transformations	O
)	O
and	O
reader	O
macros	O
(	O
input	O
parsers	O
for	O
characters	O
)	O
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
provides	O
partial	O
backwards	O
compatibility	O
with	O
Maclisp	B-Language
and	O
John	O
McCarthy	O
's	O
original	O
Lisp	B-Language
.	O
</s>
<s>
This	O
allows	O
older	O
Lisp	B-Language
software	O
to	O
be	O
ported	O
to	O
Common	B-Language
Lisp	I-Language
.	O
</s>
<s>
Work	O
on	O
Common	B-Language
Lisp	I-Language
started	O
in	O
1981	O
after	O
an	O
initiative	O
by	O
ARPA	O
manager	O
Bob	O
Engelmore	O
to	O
develop	O
a	O
single	O
community	O
standard	O
Lisp	B-Language
dialect	O
.	O
</s>
<s>
In	O
1982	O
,	O
Guy	O
L	O
.	O
Steele	O
Jr.	O
gave	O
the	O
first	O
overview	O
of	O
Common	B-Language
Lisp	I-Language
at	O
the	O
1982	O
ACM	O
Symposium	O
on	O
LISP	B-Language
and	O
functional	B-Language
programming	I-Language
.	O
</s>
<s>
The	O
first	O
language	O
documentation	O
was	O
published	O
in	O
1984	O
as	O
Common	B-Language
Lisp	I-Language
the	O
Language	O
(	O
known	O
as	O
CLtL1	O
)	O
,	O
first	O
edition	O
.	O
</s>
<s>
A	O
second	O
edition	O
(	O
known	O
as	O
CLtL2	O
)	O
,	O
published	O
in	O
1990	O
,	O
incorporated	O
many	O
changes	O
to	O
the	O
language	O
,	O
made	O
during	O
the	O
ANSI	B-Language
Common	I-Language
Lisp	I-Language
standardization	O
process	O
:	O
extended	O
LOOP	O
syntax	O
,	O
the	O
Common	B-Application
Lisp	I-Application
Object	I-Application
System	I-Application
,	O
the	O
Condition	O
System	O
for	O
error	B-General_Concept
handling	I-General_Concept
,	O
an	O
interface	O
to	O
the	O
pretty	O
printer	O
and	O
much	O
more	O
.	O
</s>
<s>
But	O
CLtL2	O
does	O
not	O
describe	O
the	O
final	O
ANSI	B-Language
Common	I-Language
Lisp	I-Language
standard	I-Language
and	O
thus	O
is	O
not	O
a	O
documentation	O
of	O
ANSI	B-Language
Common	I-Language
Lisp	I-Language
.	O
</s>
<s>
The	O
final	O
ANSI	B-Language
Common	I-Language
Lisp	I-Language
standard	I-Language
then	O
was	O
published	O
in	O
1994	O
.	O
</s>
<s>
Various	O
extensions	O
and	O
improvements	O
to	O
Common	B-Language
Lisp	I-Language
(	O
examples	O
are	O
Unicode	O
,	O
Concurrency	O
,	O
CLOS-based	O
IO	O
)	O
have	O
been	O
provided	O
by	O
implementations	O
and	O
libraries	O
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
is	O
a	O
dialect	O
of	O
Lisp	B-Language
.	O
</s>
<s>
It	O
uses	O
S-expressions	B-Protocol
to	O
denote	O
both	O
code	O
and	O
data	O
structure	O
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
has	O
many	O
data	O
types	O
.	O
</s>
<s>
Number	O
types	O
include	O
integers	O
,	O
ratios	O
,	O
floating-point	B-Algorithm
numbers	I-Algorithm
,	O
and	O
complex	O
numbers	O
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
uses	O
bignums	B-Algorithm
to	O
represent	O
numerical	O
values	O
of	O
arbitrary	O
size	O
and	O
precision	O
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
automatically	O
coerces	O
numeric	B-Algorithm
values	O
among	O
these	O
types	O
as	O
appropriate	O
.	O
</s>
<s>
The	O
Common	B-Language
Lisp	I-Language
character	O
type	O
is	O
not	O
limited	O
to	O
ASCII	B-Protocol
characters	I-Protocol
.	O
</s>
<s>
The	O
symbol	O
type	O
is	O
common	O
to	O
Lisp	B-Language
languages	I-Language
,	O
but	O
largely	O
unknown	O
outside	O
them	O
.	O
</s>
<s>
Symbols	O
in	O
Lisp	B-Language
are	O
often	O
used	O
similarly	O
to	O
identifiers	O
in	O
other	O
languages	O
:	O
to	O
hold	O
the	O
value	O
of	O
a	O
variable	O
;	O
however	O
there	O
are	O
many	O
other	O
uses	O
.	O
</s>
<s>
Boolean	O
values	O
in	O
Common	B-Language
Lisp	I-Language
are	O
represented	O
by	O
the	O
self-evaluating	O
symbols	O
T	O
and	O
NIL	B-Language
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
has	O
namespaces	O
for	O
symbols	O
,	O
called	O
'	O
packages	O
 '	O
.	O
</s>
<s>
A	O
number	O
of	O
functions	O
are	O
available	O
for	O
rounding	B-Algorithm
scalar	O
numeric	B-Algorithm
values	O
in	O
various	O
ways	O
.	O
</s>
<s>
The	O
function	O
round	O
rounds	O
the	O
argument	O
to	O
the	O
nearest	B-Algorithm
integer	I-Algorithm
,	O
with	O
halfway	O
cases	O
rounded	O
to	O
the	O
even	O
integer	O
.	O
</s>
<s>
Sequence	O
types	O
in	O
Common	B-Language
Lisp	I-Language
include	O
lists	O
,	O
vectors	O
,	O
bit-vectors	O
,	O
and	O
strings	O
.	O
</s>
<s>
As	O
in	O
almost	O
all	O
other	O
Lisp	B-Language
dialects	O
,	O
lists	O
in	O
Common	B-Language
Lisp	I-Language
are	O
composed	O
of	O
conses	O
,	O
sometimes	O
called	O
cons	O
cells	O
or	O
pairs	O
.	O
</s>
<s>
Each	O
cons	O
's	O
cdr	O
refers	O
to	O
the	O
next	O
cons	O
—	O
except	O
for	O
the	O
last	O
cons	O
in	O
a	O
list	O
,	O
whose	O
cdr	O
refers	O
to	O
the	O
nil	B-Language
value	O
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
supports	O
multidimensional	O
arrays	O
,	O
and	O
can	O
dynamically	O
resize	O
adjustable	O
arrays	O
if	O
required	O
.	O
</s>
<s>
Hash	B-Algorithm
tables	I-Algorithm
store	O
associations	O
between	O
data	O
objects	O
.	O
</s>
<s>
Hash	B-Algorithm
tables	I-Algorithm
are	O
automatically	O
resized	O
as	O
needed	O
.	O
</s>
<s>
Structures	O
,	O
similar	O
in	O
use	O
to	O
C	B-Language
structs	B-Language
and	O
Pascal	B-Application
records	O
,	O
represent	O
arbitrary	O
complex	O
data	O
structures	O
with	O
any	O
number	O
and	O
type	O
of	O
fields	O
(	O
called	O
slots	O
)	O
.	O
</s>
<s>
Classes	O
are	O
similar	O
to	O
structures	O
,	O
but	O
offer	O
more	O
dynamic	B-Language
features	O
and	O
multiple-inheritance	O
.	O
</s>
<s>
(	O
See	O
CLOS	B-Application
)	O
.	O
</s>
<s>
Classes	O
have	O
been	O
added	O
late	O
to	O
Common	B-Language
Lisp	I-Language
and	O
there	O
is	O
some	O
conceptual	O
overlap	O
with	O
structures	O
.	O
</s>
<s>
A	O
special	O
case	O
is	O
Generic	B-Language
Functions	O
.	O
</s>
<s>
Generic	B-Language
Functions	O
are	O
both	O
functions	O
and	O
instances	O
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
supports	O
first-class	B-Application
functions	I-Application
.	O
</s>
<s>
The	O
Common	B-Language
Lisp	I-Language
library	O
relies	O
heavily	O
on	O
such	O
higher-order	O
functions	O
.	O
</s>
<s>
When	O
the	O
evaluator	B-Application
encounters	O
a	O
form	O
(	O
f	O
a1	O
a2	O
...	O
)	O
then	O
it	O
presumes	O
that	O
the	O
symbol	O
named	O
f	O
is	O
one	O
of	O
the	O
following	O
:	O
</s>
<s>
The	O
name	O
of	O
a	O
function	O
(	O
default	O
)	O
,	O
which	O
may	O
either	O
be	O
a	O
symbol	O
,	O
or	O
a	O
sub-form	O
beginning	O
with	O
the	O
symbol	O
lambda	B-General_Concept
.	O
</s>
<s>
Function	O
definitions	O
may	O
include	O
compiler	B-Language
directives	O
,	O
known	O
as	O
declarations	O
,	O
which	O
provide	O
hints	O
to	O
the	O
compiler	B-Language
about	O
optimization	O
settings	O
or	O
the	O
data	O
types	O
of	O
arguments	O
.	O
</s>
<s>
They	O
may	O
also	O
include	O
documentation	O
strings	O
(	O
docstrings	O
)	O
,	O
which	O
the	O
Lisp	B-Language
system	O
may	O
use	O
to	O
provide	O
interactive	O
documentation	O
:	O
</s>
<s>
Anonymous	B-General_Concept
functions	I-General_Concept
(	O
function	B-General_Concept
literals	I-General_Concept
)	O
are	O
defined	O
using	O
lambda	B-General_Concept
expressions	I-General_Concept
,	O
e.g.	O
</s>
<s>
(	O
lambda	B-General_Concept
(	O
x	O
)	O
( *	O
x	O
x	O
)	O
)	O
for	O
a	O
function	O
that	O
squares	O
its	O
argument	O
.	O
</s>
<s>
Lisp	B-Language
programming	O
style	O
frequently	O
uses	O
higher-order	O
functions	O
for	O
which	O
it	O
is	O
useful	O
to	O
provide	O
anonymous	B-General_Concept
functions	I-General_Concept
as	O
arguments	O
.	O
</s>
<s>
For	O
instance	O
,	O
a	O
function	O
may	O
be	O
compiled	B-Language
with	O
the	O
compile	B-Language
operator	O
.	O
</s>
<s>
(	O
Some	O
Lisp	B-Language
systems	O
run	O
functions	O
using	O
an	O
interpreter	B-Application
by	O
default	O
unless	O
instructed	O
to	O
compile	B-Language
;	O
others	O
compile	B-Language
every	O
function	O
)	O
.	O
</s>
<s>
The	O
macro	O
defgeneric	O
defines	O
generic	B-Language
functions	O
.	O
</s>
<s>
Generic	B-Language
functions	O
are	O
a	O
collection	O
of	O
methods	B-Language
.	O
</s>
<s>
The	O
macro	O
defmethod	O
defines	O
methods	B-Language
.	O
</s>
<s>
Methods	B-Language
can	O
specialize	O
their	O
parameters	O
over	O
CLOS	B-Application
standard	O
classes	O
,	O
system	O
classes	O
,	O
structure	O
classes	O
or	O
individual	O
objects	O
.	O
</s>
<s>
When	O
a	O
generic	B-Language
function	O
is	O
called	O
,	O
multiple-dispatch	O
will	O
determine	O
the	O
effective	O
method	O
to	O
use	O
.	O
</s>
<s>
Generic	B-Language
Functions	O
are	O
also	O
a	O
first	O
class	O
data	O
type	O
.	O
</s>
<s>
There	O
are	O
many	O
more	O
features	O
to	O
Generic	B-Language
Functions	O
and	O
Methods	B-Language
than	O
described	O
above	O
.	O
</s>
<s>
This	O
is	O
a	O
key	O
difference	O
between	O
Common	B-Language
Lisp	I-Language
and	O
Scheme	B-Language
.	O
</s>
<s>
For	O
Common	B-Language
Lisp	I-Language
,	O
operators	O
that	O
define	O
names	O
in	O
the	O
function	O
namespace	O
include	O
defun	O
,	O
flet	O
,	O
labels	O
,	O
defmethod	O
and	O
defgeneric	O
.	O
</s>
<s>
Scheme	B-Language
's	I-Language
evaluation	O
model	O
is	O
simpler	O
:	O
there	O
is	O
only	O
one	O
namespace	O
,	O
and	O
all	O
positions	O
in	O
the	O
form	O
are	O
evaluated	O
(	O
in	O
any	O
order	O
)	O
–	O
not	O
just	O
the	O
arguments	O
.	O
</s>
<s>
For	O
instance	O
,	O
many	O
Common	B-Language
Lisp	I-Language
programmers	O
like	O
to	O
use	O
descriptive	O
variable	O
names	O
such	O
as	O
list	O
or	O
string	O
which	O
could	O
cause	O
problems	O
in	O
Scheme	B-Language
,	O
as	O
they	O
would	O
locally	O
shadow	O
function	O
names	O
.	O
</s>
<s>
Whether	O
a	O
separate	O
namespace	O
for	O
functions	O
is	O
an	O
advantage	O
is	O
a	O
source	O
of	O
contention	O
in	O
the	O
Lisp	B-Language
community	O
.	O
</s>
<s>
It	O
is	O
usually	O
referred	O
to	O
as	O
the	O
Lisp-1	O
vs.	O
Lisp-2	O
debate	O
.	O
</s>
<s>
Lisp-1	O
refers	O
to	O
Scheme	B-Language
's	I-Language
model	O
and	O
Lisp-2	O
refers	O
to	O
Common	B-Language
Lisp	I-Language
's	O
model	O
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
supports	O
the	O
concept	O
of	O
multiple	O
values	O
,	O
where	O
any	O
expression	O
always	O
has	O
a	O
single	O
primary	O
value	O
,	O
but	O
it	O
might	O
also	O
have	O
any	O
number	O
of	O
secondary	O
values	O
,	O
which	O
might	O
be	O
received	O
and	O
inspected	O
by	O
interested	O
callers	O
.	O
</s>
<s>
GETHASH	O
returns	O
the	O
value	O
of	O
a	O
key	O
in	O
an	O
associative	B-Application
map	I-Application
,	O
or	O
the	O
default	O
value	O
otherwise	O
,	O
and	O
a	O
secondary	O
boolean	O
indicating	O
whether	O
the	O
value	O
was	O
found	O
.	O
</s>
<s>
Other	O
data	O
types	O
in	O
Common	B-Language
Lisp	I-Language
include	O
:	O
</s>
<s>
Pathnames	O
represent	O
files	O
and	O
directories	O
in	O
the	O
filesystem	B-Application
.	O
</s>
<s>
The	O
Common	B-Language
Lisp	I-Language
pathname	O
facility	O
is	O
more	O
general	O
than	O
most	O
operating	O
systems	O
 '	O
file	O
naming	O
conventions	O
,	O
making	O
Lisp	B-Language
programs	O
 '	O
access	O
to	O
files	O
broadly	O
portable	O
across	O
diverse	O
systems	O
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
has	O
a	O
built-in	O
pseudo-random	B-Algorithm
number	I-Algorithm
generator	I-Algorithm
(	O
PRNG	O
)	O
.	O
</s>
<s>
Classes	O
are	O
first-class	O
objects	O
,	O
and	O
are	O
themselves	O
instances	O
of	O
classes	O
called	O
metaobject	B-Language
classes	I-Language
(	O
metaclasses	B-Language
for	O
short	O
)	O
.	O
</s>
<s>
Readtables	O
are	O
a	O
type	O
of	O
object	O
which	O
control	O
how	O
Common	B-Language
Lisp	I-Language
's	O
reader	O
parses	O
the	O
text	O
of	O
source	O
code	O
.	O
</s>
<s>
Like	O
programs	O
in	O
many	O
other	O
programming	O
languages	O
,	O
Common	B-Language
Lisp	I-Language
programs	O
make	O
use	O
of	O
names	O
to	O
refer	O
to	O
variables	O
,	O
functions	O
,	O
and	O
many	O
other	O
kinds	O
of	O
entities	O
.	O
</s>
<s>
Named	O
references	O
are	O
subject	O
to	O
scope	B-Language
.	O
</s>
<s>
Scope	B-Language
refers	O
to	O
the	O
set	O
of	O
circumstances	O
in	O
which	O
a	O
name	O
is	O
determined	O
to	O
have	O
a	O
particular	O
binding	O
.	O
</s>
<s>
The	O
circumstances	O
which	O
determine	O
scope	B-Language
in	O
Common	B-Language
Lisp	I-Language
include	O
:	O
</s>
<s>
The	O
only	O
generic	B-Language
fact	O
about	O
this	O
expression	O
is	O
that	O
defclass	O
refers	O
to	O
a	O
macro	O
binding	O
;	O
everything	O
else	O
is	O
up	O
to	O
defclass	O
.	O
</s>
<s>
For	O
instance	O
,	O
if	O
a	O
reference	O
to	O
variable	O
x	O
is	O
enclosed	O
in	O
a	O
binding	O
construct	O
such	O
as	O
a	O
let	O
which	O
defines	O
a	O
binding	O
for	O
x	O
,	O
then	O
the	O
reference	O
is	O
in	O
the	O
scope	B-Language
created	O
by	O
that	O
binding	O
.	O
</s>
<s>
This	O
determines	O
whether	O
the	O
reference	O
is	O
resolved	O
within	O
a	O
lexical	B-Language
environment	I-Language
,	O
or	O
within	O
a	O
dynamic	B-Language
environment	O
.	O
</s>
<s>
An	O
environment	O
is	O
a	O
run-time	O
dictionary	B-Application
which	O
maps	O
symbols	O
to	O
bindings	O
.	O
</s>
<s>
References	O
to	O
lexical	O
variables	O
are	O
resolved	O
in	O
a	O
lexical	B-Language
environment	I-Language
,	O
et	O
cetera	O
.	O
</s>
<s>
These	O
activations	O
share	O
the	O
same	O
program	O
text	O
,	O
but	O
each	O
has	O
its	O
own	O
lexical	B-Language
environment	I-Language
instance	O
.	O
</s>
<s>
To	O
understand	O
what	O
a	O
symbol	O
refers	O
to	O
,	O
the	O
Common	B-Language
Lisp	I-Language
programmer	O
must	O
know	O
what	O
kind	O
of	O
reference	O
is	O
being	O
expressed	O
,	O
what	O
kind	O
of	O
scope	B-Language
it	O
uses	O
if	O
it	O
is	O
a	O
variable	O
reference	O
(	O
dynamic	B-Language
versus	O
lexical	O
scope	B-Language
)	O
,	O
and	O
also	O
the	O
run-time	O
situation	O
:	O
in	O
what	O
environment	O
is	O
the	O
reference	O
resolved	O
,	O
where	O
was	O
the	O
binding	O
introduced	O
into	O
the	O
environment	O
,	O
et	O
cetera	O
.	O
</s>
<s>
Some	O
environments	O
in	O
Lisp	B-Language
are	O
globally	O
pervasive	O
.	O
</s>
<s>
One	O
type	O
of	O
environment	O
in	O
Common	B-Language
Lisp	I-Language
is	O
the	O
dynamic	B-Language
environment	O
.	O
</s>
<s>
Bindings	O
established	O
in	O
this	O
environment	O
have	O
dynamic	B-Language
extent	O
,	O
which	O
means	O
that	O
a	O
binding	O
is	O
established	O
at	O
the	O
start	O
of	O
the	O
execution	O
of	O
some	O
construct	O
,	O
such	O
as	O
a	O
let	O
block	O
,	O
and	O
disappears	O
when	O
that	O
construct	O
finishes	O
executing	O
:	O
its	O
lifetime	O
is	O
tied	O
to	O
the	O
dynamic	B-Language
activation	O
and	O
deactivation	O
of	O
a	O
block	O
.	O
</s>
<s>
However	O
,	O
a	O
dynamic	B-Language
binding	O
is	O
not	O
just	O
visible	O
within	O
that	O
block	O
;	O
it	O
is	O
also	O
visible	O
to	O
all	O
functions	O
invoked	O
from	O
that	O
block	O
.	O
</s>
<s>
This	O
type	O
of	O
visibility	O
is	O
known	O
as	O
indefinite	O
scope	B-Language
.	O
</s>
<s>
Bindings	O
which	O
exhibit	O
dynamic	B-Language
extent	O
(	O
lifetime	O
tied	O
to	O
the	O
activation	O
and	O
deactivation	O
of	O
a	O
block	O
)	O
and	O
indefinite	O
scope	B-Language
(	O
visible	O
to	O
all	O
functions	O
which	O
are	O
called	O
from	O
that	O
block	O
)	O
are	O
said	O
to	O
have	O
dynamic	B-Language
scope	B-Language
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
has	O
support	O
for	O
dynamically	B-Language
scoped	I-Language
variables	O
,	O
which	O
are	O
also	O
called	O
special	O
variables	O
.	O
</s>
<s>
Certain	O
other	O
kinds	O
of	O
bindings	O
are	O
necessarily	O
dynamically	B-Language
scoped	I-Language
also	O
,	O
such	O
as	O
restarts	O
and	O
catch	O
tags	O
.	O
</s>
<s>
Function	O
bindings	O
cannot	O
be	O
dynamically	B-Language
scoped	I-Language
using	O
flet	O
(	O
which	O
only	O
provides	O
lexically	O
scoped	B-Language
function	O
bindings	O
)	O
,	O
but	O
function	O
objects	O
(	O
a	O
first-level	O
object	O
in	O
Common	B-Language
Lisp	I-Language
)	O
can	O
be	O
assigned	O
to	O
dynamically	B-Language
scoped	I-Language
variables	O
,	O
bound	O
using	O
let	O
in	O
dynamic	B-Language
scope	B-Language
,	O
then	O
called	O
using	O
funcall	O
or	O
APPLY	O
.	O
</s>
<s>
Dynamic	B-Language
scope	B-Language
is	O
extremely	O
useful	O
because	O
it	O
adds	O
referential	O
clarity	O
and	O
discipline	O
to	O
global	O
variables	O
.	O
</s>
<s>
In	O
Common	B-Language
Lisp	I-Language
,	O
a	O
special	O
variable	O
which	O
has	O
only	O
a	O
top-level	O
binding	O
behaves	O
just	O
like	O
a	O
global	O
variable	O
in	O
other	O
programming	O
languages	O
.	O
</s>
<s>
Binding	O
a	O
dynamically	B-Language
scoped	I-Language
variable	O
temporarily	O
creates	O
a	O
new	O
memory	O
location	O
for	O
that	O
variable	O
,	O
and	O
associates	O
the	O
name	O
with	O
that	O
location	O
.	O
</s>
<s>
Of	O
course	O
,	O
multiple	O
dynamic	B-Language
bindings	O
for	O
the	O
same	O
variable	O
can	O
be	O
nested	O
.	O
</s>
<s>
In	O
Common	B-Language
Lisp	I-Language
implementations	O
which	O
support	O
multithreading	O
,	O
dynamic	B-Language
scopes	O
are	O
specific	O
to	O
each	O
thread	O
of	O
execution	O
.	O
</s>
<s>
Dynamic	B-Language
variables	O
can	O
be	O
used	O
to	O
extend	O
the	O
execution	O
context	O
with	O
additional	O
context	O
information	O
which	O
is	O
implicitly	O
passed	O
from	O
function	O
to	O
function	O
without	O
having	O
to	O
appear	O
as	O
an	O
extra	O
function	O
parameter	O
.	O
</s>
<s>
That	O
global	O
variable	O
must	O
be	O
saved	O
and	O
restored	O
,	O
so	O
that	O
the	O
scheme	B-Language
does	O
n't	O
break	O
under	O
recursion	O
:	O
dynamic	B-Language
variable	O
rebinding	O
takes	O
care	O
of	O
this	O
.	O
</s>
<s>
And	O
that	O
variable	O
must	O
be	O
made	O
thread-local	O
(	O
or	O
else	O
a	O
big	O
mutex	O
must	O
be	O
used	O
)	O
so	O
the	O
scheme	B-Language
does	O
n't	O
break	O
under	O
threads	O
:	O
dynamic	B-Language
scope	B-Language
implementations	O
can	O
take	O
care	O
of	O
this	O
also	O
.	O
</s>
<s>
In	O
the	O
Common	B-Language
Lisp	I-Language
library	O
,	O
there	O
are	O
many	O
standard	O
special	O
variables	O
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
supports	O
lexical	B-Language
environments	I-Language
.	O
</s>
<s>
Formally	O
,	O
the	O
bindings	O
in	O
a	O
lexical	B-Language
environment	I-Language
have	O
lexical	O
scope	B-Language
and	O
may	O
have	O
either	O
an	O
indefinite	O
extent	O
or	O
dynamic	B-Language
extent	O
,	O
depending	O
on	O
the	O
type	O
of	O
namespace	O
.	O
</s>
<s>
Lexical	O
scope	B-Language
means	O
that	O
visibility	O
is	O
physically	O
restricted	O
to	O
the	O
block	O
in	O
which	O
the	O
binding	O
is	O
established	O
.	O
</s>
<s>
The	O
tags	O
in	O
a	O
TAGBODY	O
have	O
lexical	O
scope	B-Language
.	O
</s>
<s>
However	O
,	O
the	O
label	O
bindings	O
disappear	O
when	O
the	O
TAGBODY	O
terminates	O
its	O
execution	O
,	O
because	O
they	O
have	O
dynamic	B-Language
extent	O
.	O
</s>
<s>
If	O
that	O
block	O
of	O
code	O
is	O
re-entered	O
by	O
the	O
invocation	O
of	O
a	O
lexical	B-Language
closure	I-Language
,	O
it	O
is	O
invalid	O
for	O
the	O
body	O
of	O
that	O
closure	B-Language
to	O
try	O
to	O
transfer	O
control	O
to	O
a	O
tag	O
via	O
GO	O
:	O
</s>
<s>
Since	O
end-label	O
is	O
at	O
the	O
end	O
of	O
the	O
tagbody	O
,	O
the	O
tagbody	O
terminates	O
,	O
yielding	O
NIL	B-Language
.	O
</s>
<s>
Local	O
function	O
bindings	O
in	O
Lisp	B-Language
have	O
lexical	O
scope	B-Language
,	O
and	O
variable	O
bindings	O
also	O
have	O
lexical	O
scope	B-Language
by	O
default	O
.	O
</s>
<s>
References	O
to	O
lexical	O
variables	O
and	O
functions	O
after	O
the	O
termination	O
of	O
their	O
establishing	O
construct	O
are	O
possible	O
thanks	O
to	O
lexical	B-Language
closures	I-Language
.	O
</s>
<s>
Lexical	O
binding	O
is	O
the	O
default	O
binding	O
mode	O
for	O
Common	B-Language
Lisp	I-Language
variables	O
.	O
</s>
<s>
For	O
an	O
individual	O
symbol	O
,	O
it	O
can	O
be	O
switched	O
to	O
dynamic	B-Language
scope	B-Language
,	O
either	O
by	O
a	O
local	O
declaration	O
,	O
by	O
a	O
global	O
declaration	O
.	O
</s>
<s>
It	O
is	O
an	O
important	O
convention	O
in	O
Common	B-Language
Lisp	I-Language
programming	O
that	O
special	O
(	O
i.e.	O
</s>
<s>
dynamically	B-Language
scoped	I-Language
)	O
variables	O
have	O
names	O
which	O
begin	O
and	O
end	O
with	O
an	O
asterisk	O
sigil	O
*	O
in	O
what	O
is	O
called	O
the	O
"	O
earmuff	B-Language
convention	I-Language
"	O
.	O
</s>
<s>
Lexical	O
scope	B-Language
is	O
useful	O
for	O
several	O
reasons	O
.	O
</s>
<s>
Firstly	O
,	O
references	O
to	O
variables	O
and	O
functions	O
can	O
be	O
compiled	B-Language
to	O
efficient	O
machine	B-Language
code	I-Language
,	O
because	O
the	O
run-time	O
environment	O
structure	O
is	O
relatively	O
simple	O
.	O
</s>
<s>
Even	O
in	O
cases	O
where	O
full	O
closures	B-Language
must	O
be	O
generated	O
,	O
access	O
to	O
the	O
closure	B-Language
's	O
environment	O
is	O
still	O
efficient	O
;	O
typically	O
each	O
variable	O
becomes	O
an	O
offset	O
into	O
a	O
vector	O
of	O
bindings	O
,	O
and	O
so	O
a	O
variable	O
reference	O
becomes	O
a	O
simple	O
load	O
or	O
store	O
instruction	O
with	O
a	O
base-plus-offset	O
addressing	B-Language
mode	I-Language
.	O
</s>
<s>
Secondly	O
,	O
lexical	O
scope	B-Language
(	O
combined	O
with	O
indefinite	O
extent	O
)	O
gives	O
rise	O
to	O
the	O
lexical	B-Language
closure	I-Language
,	O
which	O
in	O
turn	O
creates	O
a	O
whole	O
paradigm	O
of	O
programming	O
centered	O
around	O
the	O
use	O
of	O
functions	O
being	O
first-class	O
objects	O
,	O
which	O
is	O
at	O
the	O
root	O
of	O
functional	B-Language
programming	I-Language
.	O
</s>
<s>
Thirdly	O
,	O
perhaps	O
most	O
importantly	O
,	O
even	O
if	O
lexical	B-Language
closures	I-Language
are	O
not	O
exploited	O
,	O
the	O
use	O
of	O
lexical	O
scope	B-Language
isolates	O
program	O
modules	O
from	O
unwanted	O
interactions	O
.	O
</s>
<s>
For	O
situations	O
in	O
which	O
disciplined	O
interactions	O
through	O
a	O
variable	O
are	O
desirable	O
,	O
Common	B-Language
Lisp	I-Language
provides	O
special	O
variables	O
.	O
</s>
<s>
Being	O
able	O
to	O
do	O
this	O
is	O
an	O
advantage	O
,	O
and	O
being	O
able	O
to	O
prevent	O
it	O
from	O
happening	O
is	O
also	O
an	O
advantage	O
;	O
consequently	O
,	O
Common	B-Language
Lisp	I-Language
supports	O
both	O
lexical	O
and	O
dynamic	B-Language
scope	B-Language
.	O
</s>
<s>
A	O
macro	O
in	O
Lisp	B-Language
superficially	O
resembles	O
a	O
function	O
in	O
usage	O
.	O
</s>
<s>
Typical	O
uses	O
of	O
macros	O
in	O
Lisp	B-Language
:	O
</s>
<s>
Various	O
standard	O
Common	B-Language
Lisp	I-Language
features	O
also	O
need	O
to	O
be	O
implemented	O
as	O
macros	O
,	O
such	O
as	O
:	O
</s>
<s>
The	O
special	O
operator	O
macrolet	B-Language
allows	O
the	O
definition	O
of	O
local	O
(	O
lexically	O
scoped	B-Language
)	O
macros	O
.	O
</s>
<s>
It	O
is	O
also	O
possible	O
to	O
define	O
macros	O
for	O
symbols	O
using	O
define-symbol-macro	O
and	O
symbol-macrolet	O
.	O
</s>
<s>
Paul	O
Graham	O
's	O
book	O
On	O
Lisp	B-Language
describes	O
the	O
use	O
of	O
macros	O
in	O
Common	B-Language
Lisp	I-Language
in	O
detail	O
.	O
</s>
<s>
Doug	O
Hoyte	O
's	O
book	O
Let	O
Over	O
Lambda	B-General_Concept
extends	O
the	O
discussion	O
on	O
macros	O
,	O
claiming	O
"	O
Macros	O
are	O
the	O
single	O
greatest	O
advantage	O
that	O
lisp	B-Language
has	O
as	O
a	O
programming	O
language	O
and	O
the	O
single	O
greatest	O
advantage	O
of	O
any	O
programming	O
language.	O
"	O
</s>
<s>
Macros	O
allow	O
Lisp	B-Language
programmers	O
to	O
create	O
new	O
syntactic	O
forms	O
in	O
the	O
language	O
.	O
</s>
<s>
tagbody	O
is	O
a	O
primitive	O
Common	B-Language
Lisp	I-Language
special	O
operator	O
which	O
provides	O
the	O
ability	O
to	O
name	O
tags	O
and	O
use	O
the	O
go	O
form	O
to	O
jump	O
to	O
those	O
tags	O
.	O
</s>
<s>
Since	O
tagbody	O
is	O
a	O
primitive	O
operator	O
in	O
Common	B-Language
Lisp	I-Language
(	O
and	O
not	O
a	O
macro	O
)	O
,	O
it	O
will	O
not	O
be	O
expanded	O
into	O
something	O
else	O
.	O
</s>
<s>
All	O
macros	O
must	O
be	O
expanded	O
before	O
the	O
source	O
code	O
containing	O
them	O
can	O
be	O
evaluated	O
or	O
compiled	B-Language
normally	O
.	O
</s>
<s>
Macros	O
can	O
be	O
considered	O
functions	O
that	O
accept	O
and	O
return	O
S-expressions	B-Protocol
–	O
similar	O
to	O
abstract	B-Data_Structure
syntax	I-Data_Structure
trees	I-Data_Structure
,	O
but	O
not	O
limited	O
to	O
those	O
.	O
</s>
<s>
These	O
functions	O
are	O
invoked	O
before	O
the	O
evaluator	B-Application
or	O
compiler	B-Language
to	O
produce	O
the	O
final	O
source	O
code	O
.	O
</s>
<s>
Macros	O
are	O
written	O
in	O
normal	O
Common	B-Language
Lisp	I-Language
,	O
and	O
may	O
use	O
any	O
Common	B-Language
Lisp	I-Language
(	O
or	O
third-party	O
)	O
operator	O
available	O
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
macros	O
are	O
capable	O
of	O
what	O
is	O
commonly	O
called	O
variable	O
capture	O
,	O
where	O
symbols	O
in	O
the	O
macro-expansion	O
body	O
coincide	O
with	O
those	O
in	O
the	O
calling	O
context	O
,	O
allowing	O
the	O
programmer	O
to	O
create	O
macros	O
wherein	O
various	O
symbols	O
have	O
special	O
meaning	O
.	O
</s>
<s>
The	O
Scheme	B-Language
dialect	O
of	O
Lisp	B-Language
provides	O
a	O
macro-writing	O
system	O
which	O
provides	O
the	O
referential	O
transparency	O
that	O
eliminates	O
both	O
types	O
of	O
capture	O
problem	O
.	O
</s>
<s>
In	O
Common	B-Language
Lisp	I-Language
,	O
macro	O
hygiene	O
is	O
ensured	O
one	O
of	O
two	O
different	O
ways	O
.	O
</s>
<s>
However	O
,	O
packages	O
do	O
n't	O
solve	O
the	O
type	O
1	O
capture	O
of	O
references	O
to	O
standard	O
Common	B-Language
Lisp	I-Language
functions	O
and	O
operators	O
.	O
</s>
<s>
Whereas	O
the	O
Common	B-Language
Lisp	I-Language
library	O
symbols	O
are	O
external	O
,	O
and	O
frequently	O
imported	O
into	O
or	O
made	O
visible	O
in	O
user-defined	O
packages	O
.	O
</s>
<s>
The	O
until	O
macro	O
will	O
expand	O
into	O
a	O
form	O
which	O
calls	O
do	O
which	O
is	O
intended	O
to	O
refer	O
to	O
the	O
standard	O
Common	B-Language
Lisp	I-Language
macro	O
do	O
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
solves	O
the	O
problem	O
of	O
the	O
shadowing	O
of	O
standard	O
operators	O
and	O
functions	O
by	O
forbidding	O
their	O
redefinition	O
.	O
</s>
<s>
Because	O
it	O
redefines	O
the	O
standard	O
operator	O
do	O
,	O
the	O
preceding	O
is	O
actually	O
a	O
fragment	O
of	O
non-conforming	O
Common	B-Language
Lisp	I-Language
,	O
which	O
allows	O
implementations	O
to	O
diagnose	O
and	O
reject	O
it	O
.	O
</s>
<s>
The	O
condition	O
system	O
is	O
responsible	O
for	O
exception	B-General_Concept
handling	I-General_Concept
in	O
Common	B-Language
Lisp	I-Language
.	O
</s>
<s>
If	O
a	O
condition	O
is	O
signaled	O
,	O
the	O
Common	B-Language
Lisp	I-Language
system	O
searches	O
for	O
a	O
handler	O
for	O
this	O
condition	O
type	O
and	O
calls	O
the	O
handler	O
.	O
</s>
<s>
Since	O
the	O
condition	O
handler	O
is	O
called	O
in	O
the	O
context	O
of	O
the	O
error	O
(	O
without	O
unwinding	O
the	O
stack	O
)	O
,	O
full	O
error	O
recovery	O
is	O
possible	O
in	O
many	O
cases	O
,	O
where	O
other	O
exception	B-General_Concept
handling	I-General_Concept
systems	O
would	O
have	O
already	O
terminated	O
the	O
current	O
routine	O
.	O
</s>
<s>
The	O
debugger	O
itself	O
can	O
also	O
be	O
customized	O
or	O
replaced	O
using	O
the	O
*	O
debugger-hook*	O
dynamic	B-Language
variable	O
.	O
</s>
<s>
In	O
the	O
following	O
example	O
(	O
using	O
Symbolics	B-Application
Genera	I-Application
)	O
the	O
user	O
tries	O
to	O
open	O
a	O
file	O
in	O
a	O
Lisp	B-Language
function	O
test	O
called	O
from	O
the	O
Read-Eval-Print-LOOP	O
(	O
REPL	B-Application
)	O
,	O
when	O
the	O
file	O
does	O
not	O
exist	O
.	O
</s>
<s>
The	O
Lisp	B-Language
system	O
presents	O
four	O
restarts	O
.	O
</s>
<s>
The	O
user	O
selects	O
the	O
Retry	O
OPEN	O
using	O
a	O
different	O
pathname	O
restart	O
and	O
enters	O
a	O
different	O
pathname	O
(	O
lispm-init.lisp	O
instead	O
of	O
lispm-int.lisp	O
)	O
.	O
</s>
<s>
The	O
user	O
code	O
does	O
not	O
contain	O
any	O
error	B-General_Concept
handling	I-General_Concept
code	O
.	O
</s>
<s>
The	O
whole	O
error	B-General_Concept
handling	I-General_Concept
and	O
restart	O
code	O
is	O
provided	O
by	O
the	O
Lisp	B-Language
system	O
,	O
which	O
can	O
handle	O
and	O
repair	O
the	O
error	O
without	O
terminating	O
the	O
user	O
code	O
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
includes	O
a	O
toolkit	O
for	O
object-oriented	B-Language
programming	I-Language
,	O
the	O
Common	B-Application
Lisp	I-Application
Object	I-Application
System	I-Application
or	O
CLOS	B-Application
.	O
</s>
<s>
Peter	O
Norvig	O
explains	O
how	O
many	O
Design	O
Patterns	O
are	O
simpler	O
to	O
implement	O
in	O
a	O
dynamic	B-Language
language	I-Language
with	O
the	O
features	O
of	O
CLOS	B-Application
(	O
Multiple	B-Application
Inheritance	I-Application
,	O
Mixins	O
,	O
Multimethods	O
,	O
Metaclasses	B-Language
,	O
Method	O
combinations	O
,	O
etc	O
.	O
</s>
<s>
Several	O
extensions	O
to	O
Common	B-Language
Lisp	I-Language
for	O
object-oriented	B-Language
programming	I-Language
have	O
been	O
proposed	O
to	O
be	O
included	O
into	O
the	O
ANSI	B-Language
Common	I-Language
Lisp	I-Language
standard	I-Language
,	O
but	O
eventually	O
CLOS	B-Application
was	O
adopted	O
as	O
the	O
standard	O
object-system	O
for	O
Common	B-Language
Lisp	I-Language
.	O
</s>
<s>
CLOS	B-Application
is	O
a	O
dynamic	B-Language
object	B-Language
system	I-Language
with	O
multiple	O
dispatch	O
and	O
multiple	B-Application
inheritance	I-Application
,	O
and	O
differs	O
radically	O
from	O
the	O
OOP	O
facilities	O
found	O
in	O
static	O
languages	O
such	O
as	O
C++	B-Language
or	O
Java	B-Language
.	O
</s>
<s>
As	O
a	O
dynamic	B-Language
object	B-Language
system	I-Language
,	O
CLOS	B-Application
allows	O
changes	O
at	O
runtime	O
to	O
generic	B-Language
functions	O
and	O
classes	O
.	O
</s>
<s>
Methods	B-Language
can	O
be	O
added	O
and	O
removed	O
,	O
classes	O
can	O
be	O
added	O
and	O
redefined	O
,	O
objects	O
can	O
be	O
updated	O
for	O
class	O
changes	O
and	O
the	O
class	O
of	O
objects	O
can	O
be	O
changed	O
.	O
</s>
<s>
CLOS	B-Application
has	O
been	O
integrated	O
into	O
ANSI	B-Language
Common	I-Language
Lisp	I-Language
.	O
</s>
<s>
Generic	B-Language
functions	O
can	O
be	O
used	O
like	O
normal	O
functions	O
and	O
are	O
a	O
first-class	O
data	O
type	O
.	O
</s>
<s>
Every	O
CLOS	B-Application
class	O
is	O
integrated	O
into	O
the	O
Common	B-Language
Lisp	I-Language
type	O
system	O
.	O
</s>
<s>
Many	O
Common	B-Language
Lisp	I-Language
types	O
have	O
a	O
corresponding	O
class	O
.	O
</s>
<s>
There	O
is	O
more	O
potential	O
use	O
of	O
CLOS	B-Application
for	O
Common	B-Language
Lisp	I-Language
.	O
</s>
<s>
The	O
specification	B-Application
does	O
not	O
say	O
whether	O
conditions	O
are	O
implemented	O
with	O
CLOS	B-Application
.	O
</s>
<s>
Pathnames	O
and	O
streams	O
could	O
be	O
implemented	O
with	O
CLOS	B-Application
.	O
</s>
<s>
These	O
further	O
usage	O
possibilities	O
of	O
CLOS	B-Application
for	O
ANSI	B-Language
Common	I-Language
Lisp	I-Language
are	O
not	O
part	O
of	O
the	O
standard	O
.	O
</s>
<s>
Actual	O
Common	B-Language
Lisp	I-Language
implementations	O
use	O
CLOS	B-Application
for	O
pathnames	O
,	O
streams	O
,	O
input	O
–	O
output	O
,	O
conditions	O
,	O
the	O
implementation	O
of	O
CLOS	B-Application
itself	O
and	O
more	O
.	O
</s>
<s>
A	O
Lisp	B-Language
interpreter	B-Application
directly	O
executes	O
Lisp	B-Language
source	O
code	O
provided	O
as	O
Lisp	B-Language
objects	O
(	O
lists	O
,	O
symbols	O
,	O
numbers	O
,	O
...	O
)	O
read	O
from	O
s-expressions	B-Protocol
.	O
</s>
<s>
A	O
Lisp	B-Language
compiler	B-Language
generates	O
bytecode	O
or	O
machine	B-Language
code	I-Language
from	O
Lisp	B-Language
source	O
code	O
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
allows	O
both	O
individual	O
Lisp	B-Language
functions	O
to	O
be	O
compiled	B-Language
in	O
memory	O
and	O
the	O
compilation	B-Language
of	O
whole	O
files	O
to	O
externally	O
stored	O
compiled	B-Language
code	O
(	O
fasl	O
files	O
)	O
.	O
</s>
<s>
Several	O
implementations	O
of	O
earlier	O
Lisp	B-Language
dialects	O
provided	O
both	O
an	O
interpreter	B-Application
and	O
a	O
compiler	B-Language
.	O
</s>
<s>
These	O
earlier	O
Lisps	B-Language
implemented	O
lexical	O
scoping	B-Language
in	O
the	O
compiler	B-Language
and	O
dynamic	B-Language
scoping	B-Language
in	O
the	O
interpreter	B-Application
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
requires	O
that	O
both	O
the	O
interpreter	B-Application
and	O
compiler	B-Language
use	O
lexical	O
scoping	B-Language
by	O
default	O
.	O
</s>
<s>
The	O
Common	B-Language
Lisp	I-Language
standard	O
describes	O
both	O
the	O
semantics	O
of	O
the	O
interpreter	B-Application
and	O
a	O
compiler	B-Language
.	O
</s>
<s>
The	O
compiler	B-Language
can	O
be	O
called	O
using	O
the	O
function	O
compile	B-Language
for	O
individual	O
functions	O
and	O
using	O
the	O
function	O
compile-file	O
for	O
files	O
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
allows	O
type	O
declarations	O
and	O
provides	O
ways	O
to	O
influence	O
the	O
compiler	B-Language
code	O
generation	O
policy	O
.	O
</s>
<s>
For	O
the	O
latter	O
various	O
optimization	O
qualities	O
can	O
be	O
given	O
values	O
between	O
0	O
(	O
not	O
important	O
)	O
and	O
3	O
(	O
most	O
important	O
)	O
:	O
speed	O
,	O
space	O
,	O
safety	O
,	O
debug	O
and	O
compilation-speed	O
.	O
</s>
<s>
There	O
is	O
also	O
a	O
function	O
to	O
evaluate	O
Lisp	B-Language
code	O
:	O
eval	O
.	O
</s>
<s>
eval	O
takes	O
code	O
as	O
pre-parsed	O
s-expressions	B-Protocol
and	O
not	O
,	O
like	O
in	O
some	O
other	O
languages	O
,	O
as	O
text	O
strings	O
.	O
</s>
<s>
This	O
way	O
code	O
can	O
be	O
constructed	O
with	O
the	O
usual	O
Lisp	B-Language
functions	O
for	O
constructing	O
lists	O
and	O
symbols	O
and	O
then	O
this	O
code	O
can	O
be	O
evaluated	O
with	O
the	O
function	O
eval	O
.	O
</s>
<s>
Several	O
Common	B-Language
Lisp	I-Language
implementations	O
(	O
like	O
Clozure	B-Application
CL	I-Application
and	O
SBCL	B-Language
)	O
are	O
implementing	O
eval	O
using	O
their	O
compiler	B-Language
.	O
</s>
<s>
This	O
way	O
code	O
is	O
compiled	B-Language
,	O
even	O
though	O
it	O
is	O
evaluated	O
using	O
the	O
function	O
eval	O
.	O
</s>
<s>
The	O
file	O
compiler	B-Language
is	O
invoked	O
using	O
the	O
function	O
compile-file	O
.	O
</s>
<s>
The	O
generated	O
file	O
with	O
compiled	B-Language
code	O
is	O
called	O
a	O
fasl	O
(	O
from	O
fast	O
load	O
)	O
file	O
.	O
</s>
<s>
These	O
fasl	O
files	O
and	O
also	O
source	O
code	O
files	O
can	O
be	O
loaded	O
with	O
the	O
function	O
load	O
into	O
a	O
running	O
Common	B-Language
Lisp	I-Language
system	O
.	O
</s>
<s>
Depending	O
on	O
the	O
implementation	O
,	O
the	O
file	O
compiler	B-Language
generates	O
byte-code	O
(	O
for	O
example	O
for	O
the	O
Java	B-Language
Virtual	I-Language
Machine	I-Language
)	O
,	O
C	B-Language
language	I-Language
code	O
(	O
which	O
then	O
is	O
compiled	B-Language
with	O
a	O
C	B-Language
compiler	B-Language
)	O
or	O
,	O
directly	O
,	O
native	B-Language
code	I-Language
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
implementations	O
can	O
be	O
used	O
interactively	O
,	O
even	O
though	O
the	O
code	O
gets	O
fully	O
compiled	B-Language
.	O
</s>
<s>
The	O
idea	O
of	O
an	O
Interpreted	B-Application
language	I-Application
thus	O
does	O
not	O
apply	O
for	O
interactive	O
Common	B-Language
Lisp	I-Language
.	O
</s>
<s>
The	O
language	O
makes	O
a	O
distinction	O
between	O
read-time	O
,	O
compile-time	O
,	O
load-time	O
,	O
and	O
run-time	O
,	O
and	O
allows	O
user	O
code	O
to	O
also	O
make	O
this	O
distinction	O
to	O
perform	O
the	O
wanted	O
type	O
of	O
processing	O
at	O
the	O
wanted	O
step	O
.	O
</s>
<s>
This	O
distinction	O
is	O
useful	O
when	O
interactively	O
evaluating	O
,	O
compiling	B-Language
and	O
loading	O
code	O
in	O
a	O
live	O
image	O
.	O
</s>
<s>
Some	O
features	O
are	O
also	O
provided	O
to	O
help	O
writing	O
compilers	B-Language
and	O
interpreters	B-Application
.	O
</s>
<s>
The	O
Lisp	B-Language
compiler	B-Language
is	O
available	O
at	O
runtime	O
to	O
compile	B-Language
files	O
or	O
individual	O
functions	O
.	O
</s>
<s>
These	O
make	O
it	O
easy	O
to	O
use	O
Lisp	B-Language
as	O
an	O
intermediate	O
compiler	B-Language
or	O
interpreter	B-Application
for	O
another	O
language	O
.	O
</s>
<s>
By	O
convention	O
,	O
constants	O
in	O
Common	B-Language
Lisp	I-Language
are	O
enclosed	O
with	O
+	O
characters	O
.	O
</s>
<s>
Calling	O
the	O
example	O
function	O
using	O
the	O
REPL	B-Application
(	O
Read	B-Application
Eval	I-Application
Print	I-Application
Loop	I-Application
)	O
:	O
</s>
<s>
The	O
function	O
AVAILABLE-SHELLS	O
calls	O
the	O
above	O
function	O
LIST-MATCHING-LINES	O
with	O
a	O
pathname	O
and	O
an	O
anonymous	B-General_Concept
function	I-General_Concept
as	O
the	O
predicate	O
.	O
</s>
<s>
The	O
predicate	O
returns	O
the	O
pathname	O
of	O
a	O
shell	O
or	O
NIL	B-Language
(	O
if	O
the	O
string	O
is	O
not	O
the	O
filename	O
of	O
a	O
shell	O
)	O
.	O
</s>
<s>
Example	O
results	O
(	O
on	O
Mac	B-Application
OS	I-Application
X	O
10.6	O
)	O
:	O
</s>
<s>
Common	B-Language
Lisp	I-Language
is	O
most	O
frequently	O
compared	O
with	O
,	O
and	O
contrasted	O
to	O
,	O
Scheme	B-Language
—	O
if	O
only	O
because	O
they	O
are	O
the	O
two	O
most	O
popular	O
Lisp	B-Language
dialects	O
.	O
</s>
<s>
Scheme	B-Language
predates	O
CL	O
,	O
and	O
comes	O
not	O
only	O
from	O
the	O
same	O
Lisp	B-Language
tradition	O
but	O
from	O
some	O
of	O
the	O
same	O
engineers	O
—	O
Guy	O
Steele	O
,	O
with	O
whom	O
Gerald	O
Jay	O
Sussman	O
designed	O
Scheme	B-Language
,	O
chaired	O
the	O
standards	O
committee	O
for	O
Common	B-Language
Lisp	I-Language
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
is	O
a	O
general-purpose	O
programming	O
language	O
,	O
in	O
contrast	O
to	O
Lisp	B-Language
variants	O
such	O
as	O
Emacs	B-Operating_System
Lisp	I-Operating_System
and	O
AutoLISP	B-Algorithm
which	O
are	O
extension	B-Language
languages	I-Language
embedded	O
in	O
particular	O
products	O
(	O
GNU	B-Operating_System
Emacs	B-Application
and	O
AutoCAD	O
,	O
respectively	O
)	O
.	O
</s>
<s>
Unlike	O
many	O
earlier	O
Lisps	B-Language
,	O
Common	B-Language
Lisp	I-Language
(	O
like	O
Scheme	B-Language
)	O
uses	O
lexical	O
variable	O
scope	B-Language
by	O
default	O
for	O
both	O
interpreted	O
and	O
compiled	B-Language
code	O
.	O
</s>
<s>
Most	O
of	O
the	O
Lisp	B-Language
systems	O
whose	O
designs	O
contributed	O
to	O
Common	B-Language
Lisp	I-Language
—	O
such	O
as	O
ZetaLisp	B-Language
and	O
Franz	O
Lisp	B-Language
—	O
used	O
dynamically	B-Language
scoped	I-Language
variables	O
in	O
their	O
interpreters	B-Application
and	O
lexically	O
scoped	B-Language
variables	O
in	O
their	O
compilers	B-Language
.	O
</s>
<s>
Scheme	B-Language
introduced	O
the	O
sole	O
use	O
of	O
lexically	O
scoped	B-Language
variables	O
to	O
Lisp	B-Language
;	O
an	O
inspiration	O
from	O
ALGOL	B-Language
68	I-Language
.	O
</s>
<s>
CL	O
supports	O
dynamically	B-Language
scoped	I-Language
variables	O
as	O
well	O
,	O
but	O
they	O
must	O
be	O
explicitly	O
declared	O
as	O
"	O
special	O
"	O
.	O
</s>
<s>
There	O
are	O
no	O
differences	O
in	O
scoping	B-Language
between	O
ANSI	O
CL	O
interpreters	B-Application
and	O
compilers	B-Language
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
is	O
sometimes	O
termed	O
a	O
Lisp-2	O
and	O
Scheme	B-Language
a	O
Lisp-1	O
,	O
referring	O
to	O
CL	O
's	O
use	O
of	O
separate	O
namespaces	O
for	O
functions	O
and	O
variables	O
.	O
</s>
<s>
There	O
is	O
a	O
long-standing	O
controversy	O
between	O
CL	O
and	O
Scheme	B-Language
advocates	O
over	O
the	O
tradeoffs	O
involved	O
in	O
multiple	O
namespaces	O
.	O
</s>
<s>
In	O
Scheme	B-Language
,	O
it	O
is	O
(	O
broadly	O
)	O
necessary	O
to	O
avoid	O
giving	O
variables	O
names	O
which	O
clash	O
with	O
functions	O
;	O
Scheme	B-Language
functions	O
frequently	O
have	O
arguments	O
named	O
lis	O
,	O
lst	O
,	O
or	O
lyst	O
so	O
as	O
not	O
to	O
conflict	O
with	O
the	O
system	O
function	O
list	O
.	O
</s>
<s>
CL	O
also	O
differs	O
from	O
Scheme	B-Language
in	O
its	O
handling	O
of	O
boolean	O
values	O
.	O
</s>
<s>
Scheme	B-Language
uses	O
the	O
special	O
values	O
#t	O
and	O
#f	O
to	O
represent	O
truth	O
and	O
falsity	O
.	O
</s>
<s>
CL	O
follows	O
the	O
older	O
Lisp	B-Language
convention	O
of	O
using	O
the	O
symbols	O
T	O
and	O
NIL	B-Language
,	O
with	O
NIL	B-Language
standing	O
also	O
for	O
the	O
empty	O
list	O
.	O
</s>
<s>
In	O
CL	O
,	O
any	O
non-NIL	O
value	O
is	O
treated	O
as	O
true	O
by	O
conditionals	O
,	O
such	O
as	O
if	O
,	O
whereas	O
in	O
Scheme	B-Language
all	O
non-	O
#f	O
values	O
are	O
treated	O
as	O
true	O
.	O
</s>
<s>
These	O
conventions	O
allow	O
some	O
operators	O
in	O
both	O
languages	O
to	O
serve	O
both	O
as	O
predicates	O
(	O
answering	O
a	O
boolean-valued	O
question	O
)	O
and	O
as	O
returning	O
a	O
useful	O
value	O
for	O
further	O
computation	O
,	O
but	O
in	O
Scheme	B-Language
the	O
value	O
'	O
(	O
)	O
which	O
is	O
equivalent	O
to	O
NIL	B-Language
in	O
Common	B-Language
Lisp	I-Language
evaluates	O
to	O
true	O
in	O
a	O
boolean	O
expression	O
.	O
</s>
<s>
Lastly	O
,	O
the	O
Scheme	B-Language
standards	O
documents	O
require	O
tail-call	B-Language
optimization	I-Language
,	O
which	O
the	O
CL	O
standard	O
does	O
not	O
.	O
</s>
<s>
Most	O
CL	O
implementations	O
do	O
offer	O
tail-call	B-Language
optimization	I-Language
,	O
although	O
often	O
only	O
when	O
the	O
programmer	O
uses	O
an	O
optimization	O
directive	O
.	O
</s>
<s>
Nonetheless	O
,	O
common	O
CL	O
coding	O
style	O
does	O
not	O
favor	O
the	O
ubiquitous	O
use	O
of	O
recursion	O
that	O
Scheme	B-Language
style	O
prefers	O
—	O
what	O
a	O
Scheme	B-Language
programmer	O
would	O
express	O
with	O
tail	B-Language
recursion	I-Language
,	O
a	O
CL	O
user	O
would	O
usually	O
express	O
with	O
an	O
iterative	O
expression	O
in	O
do	O
,	O
dolist	O
,	O
loop	O
,	O
or	O
(	O
more	O
recently	O
)	O
with	O
the	O
iterate	O
package	O
.	O
</s>
<s>
See	O
the	O
Category	O
Common	B-Language
Lisp	I-Language
implementations	O
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
is	O
defined	O
by	O
a	O
specification	B-Application
(	O
like	O
Ada	B-Language
and	O
C	B-Language
)	O
rather	O
than	O
by	O
one	O
implementation	O
(	O
like	O
Perl	B-Language
)	O
.	O
</s>
<s>
Free	B-License
and	I-License
open-source	I-License
software	I-License
libraries	O
have	O
been	O
created	O
to	O
support	O
extensions	O
to	O
Common	B-Language
Lisp	I-Language
in	O
a	O
portable	O
way	O
,	O
and	O
are	O
most	O
notably	O
found	O
in	O
the	O
repositories	O
of	O
the	O
Common-Lisp.net	O
and	O
CLOCC	O
(	O
Common	B-Language
Lisp	I-Language
Open	O
Code	O
Collection	O
)	O
projects	O
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
implementations	O
may	O
use	O
any	O
mix	O
of	O
native	B-Language
code	B-Language
compilation	I-Language
,	O
byte	O
code	B-Language
compilation	I-Language
or	O
interpretation	O
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
has	O
been	O
designed	O
to	O
support	O
incremental	B-Application
compilers	I-Application
,	O
file	O
compilers	B-Language
and	O
block	O
compilers	B-Language
.	O
</s>
<s>
Standard	O
declarations	O
to	O
optimize	O
compilation	B-Language
(	O
such	O
as	O
function	O
inlining	O
or	O
type	O
specialization	O
)	O
are	O
proposed	O
in	O
the	O
language	O
specification	B-Application
.	O
</s>
<s>
Most	O
Common	B-Language
Lisp	I-Language
implementations	O
compile	B-Language
source	O
code	O
to	O
native	O
machine	B-Language
code	I-Language
.	O
</s>
<s>
Others	O
compile	B-Language
to	O
interpreted	O
bytecode	O
,	O
which	O
is	O
less	O
efficient	O
than	O
native	B-Language
code	I-Language
,	O
but	O
eases	O
binary-code	O
portability	O
.	O
</s>
<s>
Some	O
compilers	B-Language
compile	B-Language
Common	B-Language
Lisp	I-Language
code	O
to	O
C	B-Language
code	O
.	O
</s>
<s>
The	O
misconception	O
that	O
Lisp	B-Language
is	O
a	O
purely	O
interpreted	B-Application
language	I-Application
is	O
most	O
likely	O
because	O
Lisp	B-Language
environments	O
provide	O
an	O
interactive	O
prompt	O
and	O
that	O
code	O
is	O
compiled	B-Language
one-by-one	O
,	O
in	O
an	O
incremental	O
way	O
.	O
</s>
<s>
With	O
Common	B-Language
Lisp	I-Language
incremental	B-Application
compilation	I-Application
is	O
widely	O
used	O
.	O
</s>
<s>
Some	O
Unix-based	O
implementations	O
(	O
CLISP	B-Application
,	O
SBCL	B-Language
)	O
can	O
be	O
used	O
as	O
a	O
scripting	B-Language
language	I-Language
;	O
that	O
is	O
,	O
invoked	O
by	O
the	O
system	O
transparently	O
in	O
the	O
way	O
that	O
a	O
Perl	B-Language
or	O
Unix	B-Application
shell	I-Application
interpreter	B-Application
is	O
.	O
</s>
<s>
Allegro	B-Language
Common	I-Language
Lisp	I-Language
for	O
Microsoft	B-Application
Windows	I-Application
,	O
FreeBSD	B-Operating_System
,	O
Linux	B-Application
,	O
Apple	O
macOS	B-Application
and	O
various	O
UNIX	B-Application
variants	O
.	O
</s>
<s>
Allegro	B-Language
CL	I-Language
provides	O
an	O
Integrated	B-Application
Development	I-Application
Environment	I-Application
(	O
IDE	O
)	O
(	O
for	O
Windows	B-Application
and	O
Linux	B-Application
)	O
and	O
extensive	O
capabilities	O
for	O
application	O
delivery	O
.	O
</s>
<s>
Liquid	O
Common	B-Language
Lisp	I-Language
formerly	O
called	O
Lucid	B-Language
Common	I-Language
Lisp	I-Language
.	O
</s>
<s>
LispWorks	B-Language
for	O
Microsoft	B-Application
Windows	I-Application
,	O
FreeBSD	B-Operating_System
,	O
Linux	B-Application
,	O
Apple	O
macOS	B-Application
,	O
iOS	O
,	O
Android	O
and	O
various	O
UNIX	B-Application
variants	O
.	O
</s>
<s>
LispWorks	B-Language
provides	O
an	O
Integrated	B-Application
Development	I-Application
Environment	I-Application
(	O
IDE	O
)	O
(	O
available	O
for	O
most	O
platforms	O
,	O
but	O
not	O
for	O
iOS	O
and	O
Android	O
)	O
and	O
extensive	O
capabilities	O
for	O
application	O
delivery	O
.	O
</s>
<s>
mocl	B-Language
for	O
iOS	O
,	O
Android	O
and	O
macOS	B-Application
.	O
</s>
<s>
Open	B-Application
Genera	I-Application
for	O
DEC	O
Alpha	O
.	O
</s>
<s>
Scieneer	O
Common	B-Language
Lisp	I-Language
which	O
is	O
designed	O
for	O
high-performance	O
scientific	O
computing	O
.	O
</s>
<s>
Armed	O
Bear	O
Common	B-Language
Lisp	I-Language
(	O
ABCL	O
)	O
A	O
CL	O
implementation	O
that	O
runs	O
on	O
the	O
Java	B-Language
Virtual	I-Language
Machine	I-Language
.	O
</s>
<s>
It	O
includes	O
a	O
compiler	B-Language
to	O
Java	B-Language
byte	I-Language
code	I-Language
,	O
and	O
allows	O
access	O
to	O
Java	B-Language
libraries	O
from	O
CL	O
.	O
</s>
<s>
Clasp	O
A	O
LLVM	O
based	O
implementation	O
that	O
seamlessly	O
interoperates	O
with	O
C++	B-Language
libraries	O
.	O
</s>
<s>
Runs	O
on	O
several	O
Unix	B-Application
and	O
Unix-like	O
systems	O
(	O
including	O
macOS	B-Application
)	O
.	O
</s>
<s>
CLISP	B-Application
A	O
bytecode-compiling	O
implementation	O
,	O
portable	O
and	O
runs	O
on	O
several	O
Unix	B-Application
and	O
Unix-like	O
systems	O
(	O
including	O
macOS	B-Application
)	O
,	O
as	O
well	O
as	O
Microsoft	B-Application
Windows	I-Application
and	O
several	O
other	O
systems	O
.	O
</s>
<s>
Clozure	B-Application
CL	I-Application
(	O
CCL	O
)	O
Originally	O
a	O
free	B-License
and	I-License
open-source	I-License
fork	O
of	O
Macintosh	B-Language
Common	I-Language
Lisp	I-Language
.	O
</s>
<s>
As	O
that	O
history	O
implies	O
,	O
CCL	O
was	O
written	O
for	O
the	O
Macintosh	O
,	O
but	O
Clozure	B-Application
CL	I-Application
now	O
runs	O
on	O
macOS	B-Application
,	O
FreeBSD	B-Operating_System
,	O
Linux	B-Application
,	O
Solaris	B-Application
and	O
Windows	B-Application
.	O
</s>
<s>
32	O
and	O
64	O
bit	O
x86	B-Operating_System
ports	O
are	O
supported	O
on	O
each	O
platform	O
.	O
</s>
<s>
Additionally	O
there	O
are	O
Power	O
PC	O
ports	O
for	O
Mac	B-Application
OS	I-Application
and	O
Linux	B-Application
.	O
</s>
<s>
CCL	O
was	O
previously	O
known	O
as	O
OpenMCL	B-Application
,	O
but	O
that	O
name	O
is	O
no	O
longer	O
used	O
,	O
to	O
avoid	O
confusion	O
with	O
the	O
open	O
source	O
version	O
of	O
Macintosh	B-Language
Common	I-Language
Lisp	I-Language
.	O
</s>
<s>
CMUCL	B-Language
Originally	O
from	O
Carnegie	O
Mellon	O
University	O
,	O
now	O
maintained	O
as	O
free	B-License
and	I-License
open-source	I-License
software	I-License
by	O
a	O
group	O
of	O
volunteers	O
.	O
</s>
<s>
CMUCL	B-Language
uses	O
a	O
fast	O
native-code	O
compiler	O
.	O
</s>
<s>
It	O
is	O
available	O
on	O
Linux	B-Application
and	O
BSD	B-Operating_System
for	O
Intel	B-Operating_System
x86	I-Operating_System
;	O
Linux	B-Application
for	O
Alpha	O
;	O
macOS	B-Application
for	O
Intel	B-Operating_System
x86	I-Operating_System
and	O
PowerPC	O
;	O
and	O
Solaris	B-Application
,	O
IRIX	O
,	O
and	O
HP-UX	O
on	O
their	O
native	O
platforms	O
.	O
</s>
<s>
Corman	O
Common	B-Language
Lisp	I-Language
for	O
Microsoft	B-Application
Windows	I-Application
.	O
</s>
<s>
In	O
January	O
2015	O
Corman	O
Lisp	B-Language
has	O
been	O
published	O
under	O
MIT	O
license	O
.	O
</s>
<s>
Embeddable	B-Language
Common	I-Language
Lisp	I-Language
(	O
ECL	B-Language
)	O
ECL	B-Language
includes	O
a	O
bytecode	O
interpreter	B-Application
and	O
compiler	B-Language
.	O
</s>
<s>
It	O
can	O
also	O
compile	B-Language
Lisp	B-Language
code	O
to	O
machine	B-Language
code	I-Language
via	O
a	O
C	B-Language
compiler	B-Language
.	O
</s>
<s>
ECL	B-Language
then	O
compiles	B-Language
Lisp	B-Language
code	O
to	O
C	B-Language
,	O
compiles	B-Language
the	O
C	B-Language
code	O
with	O
a	O
C	B-Language
compiler	B-Language
and	O
can	O
then	O
load	O
the	O
resulting	O
machine	B-Language
code	I-Language
.	O
</s>
<s>
It	O
is	O
also	O
possible	O
to	O
embed	O
ECL	B-Language
in	O
C	B-Language
programs	I-Language
,	O
and	O
C	B-Language
code	O
into	O
Common	B-Language
Lisp	I-Language
programs	O
.	O
</s>
<s>
GNU	B-Application
Common	I-Application
Lisp	I-Application
(	O
GCL	B-Application
)	O
The	O
GNU	B-Operating_System
Project	O
's	O
Lisp	B-Language
compiler	B-Language
.	O
</s>
<s>
Not	O
yet	O
fully	O
ANSI-compliant	O
,	O
GCL	B-Application
is	O
however	O
the	O
implementation	O
of	O
choice	O
for	O
several	O
large	O
projects	O
including	O
the	O
mathematical	O
tools	O
Maxima	B-Language
,	O
AXIOM	B-Language
and	O
(	O
historically	O
)	O
ACL2	B-Application
.	O
</s>
<s>
GCL	B-Application
runs	O
on	O
Linux	B-Application
under	O
eleven	O
different	O
architectures	O
,	O
and	O
also	O
under	O
Windows	B-Application
,	O
Solaris	B-Application
,	O
and	O
FreeBSD	B-Operating_System
.	O
</s>
<s>
Macintosh	B-Language
Common	I-Language
Lisp	I-Language
(	O
MCL	O
)	O
Version	O
5.2	O
for	O
Apple	O
Macintosh	O
computers	O
with	O
a	O
PowerPC	O
processor	O
running	O
Mac	B-Application
OS	I-Application
X	O
is	O
open	O
source	O
.	O
</s>
<s>
ManKai	O
Common	B-Language
Lisp	I-Language
(	O
MKCL	O
)	O
A	O
branch	O
of	O
ECL	B-Language
.	O
</s>
<s>
On	O
Linux	B-Application
,	O
MKCL	O
features	O
a	O
fully	O
POSIX	O
compliant	O
runtime	O
system	O
.	O
</s>
<s>
Movitz	O
Implements	O
a	O
Lisp	B-Language
environment	O
for	O
x86	B-Operating_System
computers	O
without	O
relying	O
on	O
any	O
underlying	O
OS	O
.	O
</s>
<s>
Poplog	B-Language
Poplog	B-Language
implements	O
a	O
version	O
of	O
CL	O
,	O
with	O
POP-11	B-Language
,	O
and	O
optionally	O
Prolog	B-Language
,	O
and	O
Standard	B-Language
ML	I-Language
(	O
SML	B-Language
)	O
,	O
allowing	O
mixed	O
language	O
programming	O
.	O
</s>
<s>
For	O
all	O
,	O
the	O
implementation	O
language	O
is	O
POP-11	B-Language
,	O
which	O
is	O
compiled	B-Language
incrementally	O
.	O
</s>
<s>
It	O
also	O
has	O
an	O
integrated	O
Emacs-like	O
editor	O
that	O
communicates	O
with	O
the	O
compiler	B-Language
.	O
</s>
<s>
Steel	B-Language
Bank	I-Language
Common	I-Language
Lisp	I-Language
(	O
SBCL	B-Language
)	O
A	O
branch	O
from	O
CMUCL	B-Language
.	O
</s>
<s>
"	O
Broadly	O
speaking	O
,	O
SBCL	B-Language
is	O
distinguished	O
from	O
CMU	B-Language
CL	I-Language
by	O
a	O
greater	O
emphasis	O
on	O
maintainability.	O
"	O
</s>
<s>
SBCL	B-Language
runs	O
on	O
the	O
platforms	O
CMUCL	B-Language
does	O
,	O
except	O
HP/UX	O
;	O
in	O
addition	O
,	O
it	O
runs	O
on	O
Linux	B-Application
for	O
AMD64	O
,	O
PowerPC	O
,	O
SPARC	O
,	O
MIPS	O
,	O
Windows	B-Application
x86	B-Operating_System
and	O
has	O
experimental	O
support	O
for	O
running	O
on	O
Windows	B-Application
AMD64	O
.	O
</s>
<s>
SBCL	B-Language
does	O
not	O
use	O
an	O
interpreter	B-Application
by	O
default	O
;	O
all	O
expressions	O
are	O
compiled	B-Language
to	O
native	B-Language
code	I-Language
unless	O
the	O
user	O
switches	O
the	O
interpreter	B-Application
on	O
.	O
</s>
<s>
The	O
SBCL	B-Language
compiler	B-Language
generates	O
fast	O
native	B-Language
code	I-Language
according	O
to	O
a	O
previous	O
version	O
of	O
The	O
Computer	O
Language	O
Benchmarks	O
Game	O
.	O
</s>
<s>
Ufasoft	O
Common	B-Language
Lisp	I-Language
port	O
of	O
CLISP	B-Application
for	O
windows	B-Application
platform	O
with	O
core	O
written	O
in	O
C++	B-Language
.	O
</s>
<s>
Golden	O
Common	B-Language
Lisp	I-Language
an	O
implementation	O
for	O
the	O
PC	O
by	O
GoldHill	O
Inc	O
.	O
</s>
<s>
Kyoto	B-Language
Common	I-Language
Lisp	I-Language
the	O
first	O
Common	B-Language
Lisp	I-Language
compiler	B-Language
that	O
used	O
C	B-Language
as	O
a	O
target	O
language	O
.	O
</s>
<s>
GCL	B-Application
,	O
ECL	B-Language
and	O
MKCL	O
originate	O
from	O
this	O
Common	B-Language
Lisp	I-Language
implementation	O
.	O
</s>
<s>
Lisp	B-Operating_System
Machines	I-Operating_System
(	O
from	O
Symbolics	O
,	O
TI	O
and	O
Xerox	O
)	O
provided	O
implementations	O
of	O
Common	B-Language
Lisp	I-Language
in	O
addition	O
to	O
their	O
native	O
Lisp	B-Language
dialect	O
(	O
Lisp	B-Language
Machine	I-Language
Lisp	I-Language
or	O
Interlisp	B-Language
)	O
.	O
</s>
<s>
CLOS	B-Application
was	O
also	O
available	O
.	O
</s>
<s>
Symbolics	O
provides	O
an	O
enhanced	O
version	O
Common	B-Language
Lisp	I-Language
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
is	O
used	O
to	O
develop	O
research	O
applications	O
(	O
often	O
in	O
Artificial	B-Application
Intelligence	I-Application
)	O
,	O
for	O
rapid	O
development	O
of	O
prototypes	O
or	O
for	O
deployed	O
applications	O
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
is	O
used	O
in	O
many	O
commercial	O
applications	O
,	O
including	O
the	O
Yahoo	B-Application
!	I-Application
</s>
<s>
Store	O
web-commerce	O
site	O
,	O
which	O
originally	O
involved	O
Paul	O
Graham	O
and	O
was	O
later	O
rewritten	O
in	O
C++	B-Language
and	O
Perl	B-Language
.	O
</s>
<s>
ACT-R	B-Language
,	O
a	O
cognitive	O
architecture	O
used	O
in	O
a	O
large	O
number	O
of	O
research	O
projects	O
.	O
</s>
<s>
Cyc	B-Language
,	O
a	O
long	O
running	O
project	O
to	O
create	O
a	O
knowledge-based	O
system	O
that	O
provides	O
a	O
huge	O
amount	O
of	O
common	O
sense	O
knowledge	O
.	O
</s>
<s>
The	O
development	O
environment	O
for	O
the	O
Jak	B-Application
and	I-Application
Daxter	I-Application
video	O
game	O
series	O
,	O
developed	O
by	O
Naughty	O
Dog	O
.	O
</s>
<s>
ITA	B-Application
Software	I-Application
's	O
low	O
fare	O
search	O
engine	O
,	O
used	O
by	O
travel	O
websites	O
such	O
as	O
Orbitz	O
and	O
Kayak.com	O
and	O
airlines	O
such	O
as	O
American	O
Airlines	O
,	O
Continental	O
Airlines	O
and	O
US	O
Airways	O
.	O
</s>
<s>
Mirai	B-Language
,	O
a	O
3D	O
graphics	O
suite	O
.	O
</s>
<s>
It	O
was	O
used	O
to	O
animate	O
the	O
face	O
of	O
Gollum	B-Application
in	O
the	O
movie	O
Lord	B-Application
of	I-Application
the	I-Application
Rings	I-Application
:	I-Application
The	I-Application
Two	I-Application
Towers	I-Application
.	O
</s>
<s>
Opusmodus	O
is	O
a	O
music	O
composition	O
system	O
based	O
on	O
Common	B-Language
Lisp	I-Language
,	O
used	O
in	O
Computer	B-Application
assisted	I-Application
composition	I-Application
.	O
</s>
<s>
Prototype	B-Application
Verification	I-Application
System	I-Application
(	O
PVS	O
)	O
,	O
a	O
mechanized	O
environment	O
for	O
formal	B-Application
specification	I-Application
and	O
verification	O
.	O
</s>
<s>
PWGL	O
is	O
a	O
sophisticated	O
visual	O
programming	B-Application
environment	I-Application
based	O
on	O
Common	B-Language
Lisp	I-Language
,	O
used	O
in	O
Computer	B-Application
assisted	I-Application
composition	I-Application
and	O
sound	O
synthesis	O
.	O
</s>
<s>
Piano	O
,	O
a	O
complete	O
aircraft	O
analysis	O
suite	O
,	O
written	O
in	O
Common	B-Language
Lisp	I-Language
,	O
used	O
by	O
companies	O
like	O
Boeing	O
,	O
Airbus	O
,	O
and	O
Northrop	O
Grumman	O
.	O
</s>
<s>
Grammarly	B-Operating_System
,	O
an	O
English-language	O
writing-enhancement	O
platform	O
,	O
has	O
its	O
core	O
grammar	O
engine	O
written	O
in	O
Common	B-Language
Lisp	I-Language
.	O
</s>
<s>
The	O
Dynamic	B-Application
Analysis	I-Application
and	I-Application
Replanning	I-Application
Tool	I-Application
(	O
DART	O
)	O
,	O
which	O
is	O
said	O
to	O
alone	O
have	O
paid	O
back	O
during	O
the	O
years	O
from	O
1991	O
to	O
1995	O
for	O
all	O
thirty	O
years	O
of	O
DARPA	O
investments	O
in	O
AI	B-Application
research	I-Application
.	O
</s>
<s>
NASA	O
's	O
Jet	O
Propulsion	O
Lab	O
's	O
"	O
Deep	O
Space	O
1	O
"	O
,	O
an	O
award-winning	O
Common	B-Language
Lisp	I-Language
program	O
for	O
autopiloting	O
the	O
Deep	O
Space	O
One	O
spaceship	O
.	O
</s>
<s>
SigLab	O
,	O
a	O
Common	B-Language
Lisp	I-Language
platform	O
for	O
signal	O
processing	O
used	O
in	O
missile	O
defense	O
,	O
built	O
by	O
Raytheon	O
.	O
</s>
<s>
SPIKE	O
,	O
a	O
scheduling	O
system	O
for	O
Earth	O
or	O
space	O
based	O
observatories	O
and	O
satellites	O
,	O
notably	O
the	O
Hubble	O
Space	O
Telescope	O
,	O
written	O
in	O
Common	B-Language
Lisp	I-Language
.	O
</s>
<s>
Common	B-Language
Lisp	I-Language
has	O
been	O
used	O
for	O
prototyping	O
the	O
garbage	O
collector	O
of	O
Microsoft	O
's	O
.NET	B-Application
Common	O
Language	O
Runtime	O
.	O
</s>
<s>
The	O
original	O
version	O
of	O
Reddit	B-Application
,	O
though	O
the	O
developers	O
later	O
switched	O
to	O
Python	B-Language
due	O
to	O
the	O
lack	O
of	O
libraries	O
for	O
Common	B-Language
Lisp	I-Language
,	O
according	O
to	O
an	O
official	O
blog	O
post	O
by	O
Reddit	B-Application
co-founder	O
Steve	O
Huffman	O
.	O
</s>
<s>
There	O
also	O
exist	O
open-source	O
applications	O
written	O
in	O
Common	B-Language
Lisp	I-Language
,	O
such	O
as	O
:	O
</s>
<s>
ACL2	B-Application
,	O
a	O
full-featured	O
automated	B-Application
theorem	I-Application
prover	I-Application
for	O
an	O
applicative	B-Application
variant	O
of	O
Common	B-Language
Lisp	I-Language
.	O
</s>
<s>
Axiom	B-Language
,	O
a	O
sophisticated	O
computer	B-General_Concept
algebra	I-General_Concept
system	I-General_Concept
.	O
</s>
<s>
Maxima	B-Language
,	O
a	O
sophisticated	O
computer	B-General_Concept
algebra	I-General_Concept
system	I-General_Concept
,	O
based	O
on	O
Macsyma	O
.	O
</s>
<s>
OpenMusic	B-Language
,	O
an	O
object-oriented	B-Language
visual	O
programming	B-Application
environment	I-Application
based	O
on	O
Common	B-Language
Lisp	I-Language
,	O
used	O
in	O
Computer	B-Application
assisted	I-Application
composition	I-Application
.	O
</s>
<s>
Pgloader	O
,	O
a	O
data	O
loader	O
for	O
PostgreSQL	B-Application
,	O
which	O
was	O
re-written	O
from	O
Python	B-Language
to	O
Common	B-Language
Lisp	I-Language
.	O
</s>
<s>
Stumpwm	B-Language
,	O
a	O
tiling	O
,	O
keyboard	O
driven	O
X11	O
Window	O
Manager	O
written	O
entirely	O
in	O
Common	B-Language
Lisp	I-Language
.	O
</s>
