<s>
Dylan	B-Language
is	O
a	O
multi-paradigm	O
programming	O
language	O
that	O
includes	O
support	O
for	O
functional	B-Language
and	O
object-oriented	B-Language
programming	I-Language
(	O
OOP	O
)	O
,	O
and	O
is	O
dynamic	B-Language
and	O
reflective	B-Language
while	O
providing	O
a	O
programming	O
model	O
designed	O
to	O
support	O
generating	O
efficient	O
machine	O
code	O
,	O
including	O
fine-grained	O
control	O
over	O
dynamic	B-Language
and	O
static	O
behaviors	O
.	O
</s>
<s>
Dylan	B-Language
derives	O
from	O
Scheme	B-Language
and	O
Common	B-Language
Lisp	I-Language
and	O
adds	O
an	O
integrated	O
object	B-Language
system	I-Language
derived	O
from	O
the	O
Common	B-Application
Lisp	I-Application
Object	I-Application
System	I-Application
(	O
CLOS	B-Application
)	O
.	O
</s>
<s>
In	O
Dylan	B-Language
,	O
all	O
values	O
(	O
including	O
numbers	O
,	O
characters	O
,	O
functions	O
,	O
and	O
classes	O
)	O
are	O
first-class	O
objects	O
.	O
</s>
<s>
Dylan	B-Language
supports	O
multiple	B-Application
inheritance	I-Application
,	O
polymorphism	B-Application
,	O
multiple	O
dispatch	O
,	O
keyword	O
arguments	O
,	O
object	O
introspection	O
,	O
pattern-based	O
syntax	O
extension	O
macros	O
,	O
and	O
many	O
other	O
advanced	O
features	O
.	O
</s>
<s>
Programs	O
can	O
express	O
fine-grained	O
control	O
over	O
dynamism	O
,	O
admitting	O
programs	O
that	O
occupy	O
a	O
continuum	O
between	O
dynamic	B-Language
and	O
static	O
programming	O
and	O
supporting	O
evolutionary	O
development	O
(	O
allowing	O
for	O
rapid	O
prototyping	O
followed	O
by	O
incremental	O
refinement	O
and	O
optimization	O
)	O
.	O
</s>
<s>
Dylan	B-Language
's	O
main	O
design	O
goal	O
is	O
to	O
be	O
a	O
dynamic	B-Language
language	I-Language
well-suited	O
for	O
developing	O
commercial	B-Application
software	I-Application
.	O
</s>
<s>
Dylan	B-Language
attempts	O
to	O
address	O
potential	O
performance	O
issues	O
by	O
introducing	O
"	O
natural	O
"	O
limits	O
to	O
the	O
full	O
flexibility	O
of	O
Lisp	B-Language
systems	O
,	O
allowing	O
the	O
compiler	B-Language
to	O
clearly	O
understand	O
compilable	O
units	O
,	O
such	O
as	O
libraries	B-Library
.	O
</s>
<s>
Dylan	B-Language
derives	O
much	O
of	O
its	O
semantics	O
from	O
Scheme	B-Language
and	O
other	O
Lisps	B-Language
;	O
some	O
Dylan	B-Language
implementations	O
were	O
initially	O
built	O
within	O
extant	O
Lisp	B-Language
systems	O
.	O
</s>
<s>
However	O
,	O
Dylan	B-Language
has	O
an	O
ALGOL-like	B-Language
syntax	O
instead	O
of	O
a	O
Lisp-like	O
prefix	O
syntax	O
.	O
</s>
<s>
Dylan	B-Language
was	O
created	O
in	O
the	O
early	O
1990s	O
by	O
a	O
group	O
led	O
by	O
Apple	O
Computer	O
.	O
</s>
<s>
At	O
one	O
time	O
in	O
its	O
development	O
,	O
it	O
was	O
intended	O
for	O
use	O
with	O
the	O
Apple	B-Device
Newton	I-Device
computer	O
,	O
but	O
the	O
Dylan	B-Language
implementation	O
did	O
not	O
reach	O
sufficient	O
maturity	O
in	O
time	O
,	O
and	O
Newton	B-Device
instead	O
used	O
a	O
mix	O
of	O
C	O
and	O
the	O
NewtonScript	B-Device
developed	O
by	O
Walter	O
Smith	O
.	O
</s>
<s>
Apple	O
ended	O
their	O
Dylan	B-Language
development	O
effort	O
in	O
1995	O
,	O
though	O
they	O
made	O
a	O
"	O
technology	O
release	O
"	O
version	O
available	O
(	O
Apple	O
Dylan	B-Language
TR1	O
)	O
that	O
included	O
an	O
advanced	O
integrated	B-Application
development	I-Application
environment	I-Application
(	O
IDE	O
)	O
.	O
</s>
<s>
Two	O
other	O
groups	O
contributed	O
to	O
the	O
design	O
of	O
the	O
language	O
and	O
developed	O
implementations	O
:	O
Harlequin	O
released	O
a	O
commercial	O
IDE	O
for	O
Microsoft	B-Application
Windows	I-Application
and	O
Carnegie	O
Mellon	O
University	O
released	O
an	O
open	B-Application
source	I-Application
compiler	B-Language
for	O
Unix	B-Application
systems	I-Application
called	O
Gwydion	B-Language
Dylan	I-Language
.	O
</s>
<s>
Both	O
of	O
these	O
implementations	O
are	O
now	O
open	B-Application
source	I-Application
.	O
</s>
<s>
The	O
Harlequin	O
implementation	O
is	O
now	O
named	O
Open	B-Language
Dylan	I-Language
and	O
is	O
maintained	O
by	O
a	O
group	O
of	O
volunteers	O
,	O
the	O
Dylan	B-Language
Hackers	O
.	O
</s>
<s>
The	O
Dylan	B-Language
language	I-Language
was	O
code-named	O
Ralph	O
.	O
</s>
<s>
James	O
Joaquin	O
chose	O
the	O
name	O
Dylan	B-Language
for	O
"	O
DYnamic	O
LANguage.	O
"	O
</s>
<s>
Many	O
of	O
Dylan	B-Language
's	O
syntax	O
features	O
come	O
from	O
its	O
Lisp	B-Language
heritage	O
.	O
</s>
<s>
Originally	O
,	O
Dylan	B-Language
used	O
a	O
Lisp-like	O
prefix	O
syntax	O
,	O
which	O
was	O
based	O
on	O
s-expressions	B-Protocol
.	O
</s>
<s>
By	O
the	O
time	O
the	O
language	O
design	O
was	O
completed	O
,	O
the	O
syntax	O
was	O
changed	O
to	O
an	O
ALGOL-like	B-Language
syntax	O
,	O
with	O
the	O
expectation	O
that	O
it	O
would	O
be	O
more	O
familiar	O
to	O
a	O
wider	O
audience	O
of	O
programmers	O
.	O
</s>
<s>
It	O
is	O
described	O
in	O
great	O
detail	O
in	O
the	O
Dylan	B-Language
Reference	O
Manual	O
.	O
</s>
<s>
Dylan	B-Language
is	O
not	O
case	O
sensitive	O
.	O
</s>
<s>
Dylan	B-Language
's	O
lexical	B-Application
syntax	I-Application
allows	O
the	O
use	O
of	O
a	O
naming	O
convention	O
where	O
hyphen	O
(	O
minus	O
)	O
signs	O
are	O
used	O
to	O
connect	O
the	O
parts	O
of	O
multiple-word	O
identifiers	O
(	O
sometimes	O
called	O
"	O
lisp-case	O
"	O
or	O
"	O
kebab	O
case	O
"	O
)	O
.	O
</s>
<s>
This	O
convention	O
is	O
common	O
in	O
Lisp	B-Language
languages	I-Language
.	O
</s>
<s>
Besides	O
alphanumeric	O
characters	O
and	O
hyphen-minus	O
signs	O
,	O
Dylan	B-Language
allows	O
a	O
variety	O
of	O
non-alphanumeric	O
characters	O
as	O
part	O
of	O
identifiers	O
.	O
</s>
<s>
There	O
is	O
no	O
explicit	O
return	B-Language
statement	I-Language
.	O
</s>
<s>
In	O
many	O
object-oriented	B-Language
languages	I-Language
,	O
classes	O
are	O
the	O
main	O
means	O
of	O
encapsulation	O
and	O
modularity	O
;	O
each	O
class	O
defines	O
a	O
namespace	O
and	O
controls	O
which	O
definitions	O
are	O
externally	O
visible	O
.	O
</s>
<s>
For	O
example	O
,	O
using	O
a	O
String	O
concatenation	O
function	O
requires	O
importing	O
and	O
compiling	B-Language
against	O
all	O
of	O
String	O
.	O
</s>
<s>
Some	O
languages	O
,	O
including	O
Dylan	B-Language
,	O
also	O
include	O
a	O
separate	O
,	O
explicit	O
namespace	O
or	O
module	O
system	O
that	O
performs	O
encapsulation	O
in	O
a	O
more	O
general	O
way	O
.	O
</s>
<s>
In	O
Dylan	B-Language
,	O
the	O
concepts	O
of	O
compile-unit	O
and	O
import-unit	O
are	O
separated	O
,	O
and	O
classes	O
have	O
nothing	O
specifically	O
to	O
do	O
with	O
either	O
.	O
</s>
<s>
A	O
library	O
defines	O
items	O
that	O
should	O
be	O
compiled	B-Language
and	O
handled	O
together	O
,	O
while	O
a	O
module	O
defines	O
a	O
namespace	O
.	O
</s>
<s>
For	O
example	O
,	O
consider	O
an	O
add-on	O
library	O
for	O
regex	B-Language
support	O
on	O
String	O
.	O
</s>
<s>
As	O
soon	O
as	O
this	O
occurs	O
,	O
the	O
String	O
class	O
becomes	O
larger	O
,	O
and	O
functions	O
that	O
do	O
n't	O
need	O
to	O
use	O
regex	B-Language
still	O
must	O
"	O
pay	O
"	O
for	O
it	O
in	O
increased	O
library	O
size	O
.	O
</s>
<s>
Under	O
Dylan	B-Language
,	O
many	O
interfaces	O
can	O
be	O
defined	O
for	O
the	O
same	O
code	O
,	O
for	O
instance	O
the	O
String	O
concatenation	O
method	O
could	O
be	O
placed	O
in	O
both	O
the	O
String	O
interface	O
,	O
and	O
the	O
"	O
concat	O
"	O
interface	O
which	O
collects	O
together	O
all	O
of	O
the	O
different	O
concatenation	O
functions	O
from	O
various	O
classes	O
.	O
</s>
<s>
This	O
is	O
more	O
commonly	O
used	O
in	O
math	O
libraries	B-Library
,	O
where	O
functions	O
tend	O
to	O
be	O
applicable	O
to	O
widely	O
differing	O
object	O
types	O
.	O
</s>
<s>
Under	O
Dylan	B-Language
,	O
every	O
function	O
call	O
can	O
be	O
simply	O
placed	O
in	O
the	O
"	O
Private	O
"	O
or	O
"	O
Development	O
"	O
interface	O
,	O
and	O
collect	O
up	O
publicly	O
accessible	O
functions	O
in	O
Public	O
.	O
</s>
<s>
Under	O
Java	B-Language
or	O
C++	B-Language
the	O
visibility	O
of	O
an	O
object	O
is	O
defined	O
in	O
the	O
code	O
,	O
meaning	O
that	O
to	O
support	O
a	O
similar	O
change	O
,	O
a	O
programmer	O
would	O
be	O
forced	O
to	O
rewrite	O
the	O
definitions	O
fully	O
,	O
and	O
could	O
not	O
have	O
two	O
versions	O
at	O
the	O
same	O
time	O
.	O
</s>
<s>
Classes	O
in	O
Dylan	B-Language
describe	O
slots	O
(	O
data	O
members	O
,	O
fields	O
,	O
ivars	O
,	O
etc	O
.	O
)	O
</s>
<s>
All	O
access	O
to	O
slots	O
is	O
via	O
methods	O
,	O
as	O
in	O
Smalltalk	B-Application
.	O
</s>
<s>
In	O
contrast	O
with	O
most	O
other	O
OO	O
languages	O
,	O
other	O
methods	O
applicable	O
to	O
the	O
class	O
are	O
often	O
defined	O
outside	O
of	O
the	O
class	O
,	O
and	O
thus	O
class	O
definitions	O
in	O
Dylan	B-Language
typically	O
include	O
the	O
definition	O
of	O
the	O
storage	O
only	O
.	O
</s>
<s>
In	O
languages	O
such	O
as	O
C++	B-Language
or	O
Java	B-Language
,	O
the	O
class	O
would	O
also	O
define	O
its	O
interface	O
.	O
</s>
<s>
In	O
Dylan	B-Language
,	O
these	O
sorts	O
of	O
visibility	O
rules	O
are	O
not	O
considered	O
part	O
of	O
the	O
code	O
,	O
but	O
of	O
the	O
module/interface	O
system	O
.	O
</s>
<s>
With	O
C++	B-Language
or	O
Java	B-Language
these	O
changes	O
would	O
require	O
changes	O
to	O
the	O
source	O
code	O
,	O
so	O
people	O
wo	O
n't	O
do	O
it	O
,	O
whereas	O
in	O
Dylan	B-Language
this	O
is	O
a	O
fully	O
unrelated	O
concept	O
.	O
</s>
<s>
Although	O
this	O
example	O
does	O
not	O
use	O
it	O
,	O
Dylan	B-Language
also	O
supports	O
multiple	B-Application
inheritance	I-Application
.	O
</s>
<s>
In	O
Dylan	B-Language
,	O
methods	O
are	O
not	O
intrinsically	O
associated	O
with	O
any	O
specific	O
class	O
;	O
methods	O
can	O
be	O
thought	O
of	O
as	O
existing	O
outside	O
of	O
classes	O
.	O
</s>
<s>
Like	O
CLOS	B-Application
,	O
Dylan	B-Language
is	O
based	O
on	O
multiple	O
dispatch	O
(	O
multimethods	O
)	O
,	O
where	O
the	O
specific	O
method	O
to	O
be	O
called	O
is	O
chosen	O
based	O
on	O
the	O
types	O
of	O
all	O
its	O
arguments	O
.	O
</s>
<s>
The	O
method	O
need	O
not	O
be	O
known	O
at	O
compile	B-Language
time	O
,	O
the	O
understanding	O
being	O
that	O
the	O
required	O
function	O
may	O
be	O
available	O
,	O
or	O
not	O
,	O
based	O
on	O
a	O
user	O
's	O
preferences	O
.	O
</s>
<s>
Under	O
Java	B-Language
the	O
same	O
methods	O
would	O
be	O
isolated	O
in	O
a	O
specific	O
class	O
.	O
</s>
<s>
If	O
that	O
class	O
is	O
unavailable	O
,	O
or	O
unknown	O
at	O
compile	B-Language
time	O
,	O
the	O
application	O
simply	O
wo	O
n't	O
compile	B-Language
.	O
</s>
<s>
In	O
Dylan	B-Language
,	O
code	O
is	O
isolated	O
from	O
storage	O
in	O
functions	O
.	O
</s>
<s>
For	O
instance	O
,	O
one	O
common	O
function	O
in	O
most	O
languages	O
is	O
the	O
to-string	O
,	O
which	O
returns	O
some	O
human-readable	B-General_Concept
form	O
for	O
the	O
object	O
.	O
</s>
<s>
In	O
Dylan	B-Language
these	O
methods	O
could	O
all	O
be	O
collected	O
into	O
a	O
single	O
module	O
called	O
"	O
to-string	O
"	O
,	O
thereby	O
removing	O
this	O
code	O
from	O
the	O
definition	O
of	O
the	O
class	O
itself	O
.	O
</s>
<s>
This	O
might	O
not	O
make	O
any	O
sense	O
until	O
you	O
consider	O
how	O
Dylan	B-Language
handles	O
the	O
call	O
of	O
the	O
to-string	O
.	O
</s>
<s>
In	O
most	O
languages	O
when	O
the	O
program	O
is	O
compiled	B-Language
the	O
to-string	O
for	O
<window>	O
is	O
looked	O
up	O
and	O
replaced	O
with	O
a	O
pointer	O
(	O
more	O
or	O
less	O
)	O
to	O
the	O
method	O
.	O
</s>
<s>
In	O
Dylan	B-Language
this	O
occurs	O
when	O
the	O
program	O
is	O
first	O
run	O
;	O
the	O
runtime	B-Device
builds	O
a	O
table	O
of	O
method-name/parameters	O
details	O
and	O
looks	O
up	O
methods	O
dynamically	O
via	O
this	O
table	O
.	O
</s>
<s>
That	O
means	O
that	O
a	O
function	O
for	O
a	O
specific	O
method	O
can	O
be	O
located	O
anywhere	O
,	O
not	O
just	O
in	O
the	O
compile-time	O
unit	O
.	O
</s>
<s>
In	O
the	O
end	O
the	O
programmer	O
is	O
given	O
considerable	O
flexibility	O
in	O
terms	O
of	O
where	O
to	O
place	O
their	O
code	O
,	O
collecting	O
it	O
along	O
class	O
lines	O
where	O
appropriate	O
,	O
and	O
functional	B-Language
lines	O
where	O
it	O
's	O
not	O
.	O
</s>
<s>
For	O
instance	O
,	O
you	O
might	O
wish	O
to	O
add	O
spell	O
checking	O
to	O
all	O
<	O
string>s	O
,	O
which	O
in	O
C++	B-Language
or	O
Java	B-Language
would	O
require	O
access	O
to	O
the	O
source	O
code	O
of	O
the	O
string	O
classand	O
such	O
basic	O
classes	O
are	O
rarely	O
given	O
out	O
in	O
source	O
form	O
.	O
</s>
<s>
In	O
Dylan	B-Language
(	O
and	O
other	O
"	O
extensible	O
languages	O
"	O
)	O
the	O
spell	O
checking	O
method	O
could	O
be	O
added	O
in	O
the	O
spell-check	O
module	O
,	O
defining	O
all	O
of	O
the	O
classes	O
on	O
which	O
it	O
can	O
be	O
applied	O
via	O
the	O
define	O
method	O
construct	O
.	O
</s>
<s>
When	O
the	O
spell-check	O
module	O
is	O
compiled	B-Language
into	O
your	O
program	O
,	O
all	O
strings	O
(	O
and	O
other	O
objects	O
)	O
will	O
get	O
the	O
added	O
functionality	O
.	O
</s>
<s>
Apple	O
Dylan	B-Language
is	O
the	O
implementation	O
of	O
Dylan	B-Language
produced	O
by	O
Apple	O
Computer	O
.	O
</s>
<s>
It	O
was	O
originally	O
developed	O
for	O
the	O
Apple	B-Device
Newton	I-Device
product	O
.	O
</s>
