<s>
Io	B-Application
is	O
a	O
pure	O
object-oriented	B-Language
programming	I-Language
language	I-Language
inspired	O
by	O
Smalltalk	B-Application
,	O
Self	B-Operating_System
,	O
Lua	B-Language
,	O
Lisp	B-Language
,	O
Act1	O
,	O
and	O
NewtonScript	B-Device
.	O
</s>
<s>
Io	B-Application
has	O
a	O
prototype-based	B-Application
object	O
model	O
similar	O
to	O
the	O
ones	O
in	O
Self	B-Operating_System
and	O
NewtonScript	B-Device
,	O
eliminating	O
the	O
distinction	O
between	O
instance	O
and	O
class	O
.	O
</s>
<s>
Like	O
Smalltalk	B-Application
,	O
everything	O
is	O
an	O
object	O
and	O
it	O
uses	O
dynamic	O
typing	O
.	O
</s>
<s>
Like	O
Lisp	B-Language
,	O
programs	O
are	O
just	O
data	O
trees	O
.	O
</s>
<s>
Io	B-Application
uses	O
actors	O
for	O
concurrency	B-Operating_System
.	O
</s>
<s>
Remarkable	O
features	O
of	O
Io	B-Application
are	O
its	O
minimal	O
size	O
and	O
openness	O
to	O
using	O
external	O
code	O
resources	O
.	O
</s>
<s>
Io	B-Application
is	O
executed	O
by	O
a	O
small	O
,	O
portable	O
virtual	B-Architecture
machine	I-Architecture
.	O
</s>
<s>
Io	B-Application
's	O
goal	O
is	O
to	O
explore	O
conceptual	O
unification	O
and	O
dynamic	B-Language
languages	I-Language
,	O
so	O
the	O
tradeoffs	O
tend	O
to	O
favor	O
simplicity	O
and	O
flexibility	O
over	O
performance	O
.	O
</s>
<s>
Assuming	O
the	O
above	O
doStuff	O
is	O
a	O
method	B-Language
,	O
it	O
is	O
being	O
called	O
with	O
zero	O
arguments	O
and	O
as	O
a	O
result	O
,	O
explicit	O
parentheses	O
are	O
not	O
required	O
.	O
</s>
<s>
Io	B-Application
is	O
a	O
message	B-Architecture
passing	I-Architecture
language	O
,	O
and	O
since	O
everything	O
in	O
Io	B-Application
is	O
a	O
message	O
(	O
excluding	O
comments	O
)	O
,	O
each	O
message	O
is	O
sent	O
to	O
a	O
receiver	O
.	O
</s>
<s>
The	O
above	O
example	O
demonstrates	O
message	B-Architecture
passing	I-Architecture
in	O
Io	B-Application
;	O
the	O
"	O
version	O
"	O
message	O
is	O
sent	O
to	O
the	O
"	O
System	O
"	O
object	O
.	O
</s>
<s>
The	O
Io	B-Application
parser	B-Language
intercepts	O
a	O
set	O
of	O
operators	O
defined	O
by	O
the	O
interpreter	O
,	O
and	O
translates	O
them	O
to	O
method	B-Language
calls	I-Language
.	O
</s>
<s>
All	O
operators	O
in	O
Io	B-Application
are	O
methods	O
;	O
the	O
fact	O
that	O
they	O
do	O
not	O
require	O
explicit	O
parentheses	O
is	O
a	O
convenience	O
.	O
</s>
<s>
In	O
Io	B-Application
there	O
are	O
two	O
ways	O
of	O
creating	O
anonymous	B-General_Concept
functions	I-General_Concept
:	O
methods	O
and	O
blocks	O
.	O
</s>
<s>
Between	O
them	O
,	O
they	O
are	O
almost	O
identical	O
except	O
for	O
scope	B-Language
.	O
</s>
<s>
While	O
blocks	O
have	O
lexical	O
scope	B-Language
,	O
methods	O
have	O
dynamic	O
scope	B-Language
.	O
</s>
<s>
Both	O
method	B-Language
and	O
block	O
are	O
higher-order	B-Language
functions	I-Language
.	O
</s>
<s>
New	O
objects	O
are	O
created	O
by	O
cloning	B-Application
objects	O
.	O
</s>
<s>
In	O
Io	B-Application
specifically	O
,	O
a	O
new	O
,	O
empty	O
object	O
is	O
created	O
and	O
only	O
the	O
differences	O
between	O
it	O
and	O
its	O
parent	O
are	O
stored	O
within	O
the	O
new	O
object	O
;	O
this	O
behavior	O
is	O
known	O
as	O
differential	B-Application
inheritance	I-Application
.	O
</s>
<s>
A	O
simple	O
non-recursive	O
factorial	O
function	O
,	O
in	O
Io	B-Application
:	O
</s>
<s>
The	O
above	O
demonstrates	O
the	O
usage	O
of	O
ranges	B-Data_Structure
,	O
and	O
does	O
n't	O
use	O
a	O
for( )	O
loop	O
,	O
which	O
would	O
be	O
faster	O
.	O
</s>
