<s>
Rebol	B-Application
(	O
;	O
historically	O
REBOL	B-Application
)	O
is	O
a	O
cross-platform	B-Operating_System
data	O
exchange	O
language	O
and	O
a	O
multi-paradigm	O
dynamic	B-Language
programming	I-Language
language	I-Language
designed	O
by	O
Carl	O
Sassenrath	O
for	O
network	O
communications	O
and	O
distributed	B-Architecture
computing	I-Architecture
.	O
</s>
<s>
It	O
introduces	O
the	O
concept	O
of	O
dialecting	O
:	O
small	O
,	O
optimized	O
,	O
domain-specific	B-Language
languages	I-Language
for	O
code	O
and	O
data	O
,	O
which	O
is	O
also	O
the	O
most	O
notable	O
property	O
of	O
the	O
language	O
according	O
to	O
its	O
designer	O
Carl	O
Sassenrath	O
:	O
</s>
<s>
Douglas	O
Crockford	O
,	O
known	O
for	O
his	O
involvement	O
in	O
the	O
development	O
of	O
JavaScript	B-Language
,	O
has	O
described	O
Rebol	B-Application
as	O
"	O
a	O
more	O
modern	O
language	O
,	O
but	O
with	O
some	O
very	O
similar	O
ideas	O
to	O
Lisp	B-Language
,	O
in	O
that	O
it	O
's	O
all	O
built	O
upon	O
a	O
representation	O
of	O
data	O
which	O
is	O
then	O
executable	O
as	O
programs	O
"	O
and	O
as	O
one	O
of	O
JSON	B-General_Concept
's	O
influences	O
.	O
</s>
<s>
Originally	O
,	O
the	O
language	O
and	O
its	O
official	O
implementation	O
were	O
proprietary	B-Application
and	O
closed	B-Application
source	I-Application
,	O
developed	O
by	O
REBOL	B-Application
Technologies	O
.	O
</s>
<s>
Following	O
discussion	O
with	O
Lawrence	O
Rosen	O
,	O
the	O
Rebol	B-Application
version	O
3	O
interpreter	B-Application
was	O
released	O
under	O
the	O
Apache	B-Application
2.0	I-Application
license	I-Application
on	O
December	O
12	O
,	O
2012	O
.	O
</s>
<s>
Rebol	B-Application
has	O
been	O
used	O
to	O
program	O
Internet	O
applications	O
(	O
both	O
client	B-Operating_System
-	I-Operating_System
and	O
server-side	B-Application
)	O
,	O
database	O
applications	O
,	O
utilities	B-Application
,	O
and	O
multimedia	O
applications	O
.	O
</s>
<s>
Rebol	B-Application
was	O
initially	O
an	O
acronym	O
for	O
Relative	O
Expression	O
Based	O
Object	O
Language	O
written	O
in	O
all	O
caps	O
.	O
</s>
<s>
by	O
the	O
change	O
replacing	O
historical	O
name	O
LISP	B-Language
by	O
Lisp	B-Language
,	O
programmers	O
ceased	O
the	O
practice	O
of	O
writing	O
REBOL	B-Application
in	O
all	O
caps	O
.	O
</s>
<s>
In	O
subsequent	O
writing	O
,	O
Sassenrath	O
adopted	O
the	O
convention	O
of	O
writing	O
the	O
language	O
name	O
as	O
Rebol	B-Application
.	O
</s>
<s>
First	O
released	O
in	O
1997	O
,	O
Rebol	B-Application
was	O
designed	O
over	O
a	O
20-year	O
period	O
by	O
Carl	O
Sassenrath	O
,	O
the	O
architect	O
and	O
primary	O
developer	O
of	O
AmigaOS	B-Application
,	O
based	O
on	O
his	O
study	O
of	O
denotational	B-Application
semantics	I-Application
and	O
using	O
concepts	O
from	O
the	O
programming	O
languages	O
Lisp	B-Language
,	O
Forth	B-Application
,	O
Logo	B-Device
,	O
and	O
Self	B-Operating_System
.	O
</s>
<s>
REBOL	B-Application
Technologies	O
was	O
founded	O
in	O
1998	O
.	O
</s>
<s>
REBOL	B-Application
2	O
,	O
the	O
interpreter	B-Application
,	O
which	O
became	O
the	O
core	O
of	O
extended	O
interpreter	B-Application
editions	O
,	O
was	O
first	O
released	O
in	O
1999	O
.	O
</s>
<s>
REBOL/Command	O
,	O
which	O
added	O
strong	O
encryption	O
and	O
ODBC	B-Application
access	O
,	O
was	O
released	O
in	O
September	O
2000	O
.	O
</s>
<s>
REBOL/View	O
was	O
released	O
in	O
April	O
2001	O
,	O
adding	O
graphical	O
abilities	O
on	O
the	O
core	O
language	O
.	O
</s>
<s>
REBOL/IOS	O
,	O
an	O
extensible	O
collaboration	O
environment	O
built	O
with	O
REBOL	B-Application
was	O
released	O
in	O
August	O
2001	O
.	O
</s>
<s>
REBOL/SDK	O
,	O
providing	O
a	O
choice	O
of	O
kernels	O
to	O
bind	O
against	O
,	O
as	O
well	O
as	O
a	O
preprocessor	O
,	O
was	O
released	O
in	O
December	O
2002	O
.	O
</s>
<s>
Rebol	B-Application
3	O
[R3],	O
the	O
newest	O
version	O
of	O
the	O
interpreter	B-Application
,	O
had	O
alpha	O
versions	O
released	O
by	O
REBOL	B-Application
Technologies	O
since	O
January	O
2008	O
.	O
</s>
<s>
Since	O
its	O
release	O
as	O
an	O
Apache	O
2	O
project	O
in	O
December	O
2012	O
,	O
it	O
is	O
being	O
developed	O
by	O
the	O
Rebol	B-Application
community	O
.	O
</s>
<s>
One	O
of	O
the	O
Rebol	B-Application
design	O
principles	O
is	O
"	O
to	O
do	O
simple	O
things	O
in	O
simple	O
ways	O
"	O
.	O
</s>
<s>
In	O
the	O
following	O
example	O
the	O
Visual	O
interface	O
dialect	O
is	O
used	O
to	O
describe	O
a	O
simple	O
Hello	O
world	O
program	O
with	O
a	O
graphical	B-Application
user	I-Application
interface	I-Application
:	O
</s>
<s>
This	O
is	O
how	O
a	O
similar	O
example	O
looks	O
in	O
R3-GUI	O
:	O
</s>
<s>
Rebol	B-Application
domain-specific	B-Language
languages	I-Language
,	O
called	O
dialects	O
,	O
are	O
micro-languages	O
optimized	O
for	O
a	O
specific	O
purpose	O
.	O
</s>
<s>
Dialects	O
can	O
be	O
used	O
to	O
define	O
business	O
rules	O
,	O
graphical	B-Application
user	I-Application
interfaces	I-Application
or	O
sequences	O
of	O
screens	O
during	O
the	O
installation	O
of	O
a	O
program	O
.	O
</s>
<s>
Users	O
can	O
define	O
their	O
own	O
dialects	O
,	O
reusing	O
any	O
existing	O
Rebol	B-Application
word	O
and	O
giving	O
it	O
a	O
specific	O
meaning	O
in	O
that	O
dialect	O
.	O
</s>
<s>
Dialects	O
are	O
interpreted	B-Application
by	O
functions	O
processing	O
Rebol	B-Application
blocks	O
(	O
or	O
parsing	O
strings	O
)	O
in	O
a	O
specific	O
way	O
.	O
</s>
<s>
An	O
example	O
of	O
Rebol	B-Application
's	O
dialecting	O
abilities	O
can	O
be	O
seen	O
with	O
the	O
word	O
return	O
.	O
</s>
<s>
A	O
Rebol	B-Application
interpreter	B-Application
with	O
graphical	O
abilities	O
must	O
understand	O
and	O
interpret	O
many	O
dialects	O
.	O
</s>
<s>
Dialect	O
name	O
Interpreted	B-Application
by	O
Purpose	O
Data	O
exchange	O
dialect	O
load	O
function	O
represents	O
data	O
and	O
metadata	O
;	O
common	O
platform	O
for	O
Rebol	B-Application
dialects	O
Do	O
dialect	O
do	O
function	O
programming	O
Parse	O
dialect	O
parse	O
function	O
pattern	B-Language
matching	I-Language
Function	O
specification	O
dialect	O
make	O
function	O
function	O
definition	O
;	O
functional	B-Language
programming	I-Language
Object	O
specification	O
dialect	O
make	O
function	O
object	O
definition/inheritance	O
;	O
prototype-based	B-Application
programming	I-Application
Visual	O
interface	O
dialect	O
(	O
VID	O
)	O
orRebGUI	O
layout	O
functionordisplay	O
function	O
specifies	O
graphical	B-Application
user	I-Application
interface	I-Application
Draw	O
dialect	O
view	O
function	O
defines	O
graphical	O
elements	O
(	O
lines	O
,	O
polygons	O
,	O
etc	O
.	O
)	O
</s>
<s>
Rebol	B-Application
syntax	O
is	O
free-form	B-Language
,	O
not	O
requiring	O
specific	O
positioning	O
.	O
</s>
<s>
The	O
common	O
platform	O
for	O
all	O
Rebol	B-Application
dialects	O
is	O
the	O
data	O
exchange	O
dialect	O
;	O
other	O
dialects	O
are	O
usually	O
derived	O
from	O
it	O
.	O
</s>
<s>
In	O
contrast	O
to	O
programming	O
languages	O
like	O
C	B-Language
,	O
the	O
data	O
exchange	O
dialect	O
does	O
not	O
consist	O
of	O
declarations	O
,	O
statements	O
,	O
expressions	O
or	O
keywords	O
.	O
</s>
<s>
A	O
valid	O
data	O
exchange	O
dialect	O
text	O
stream	O
is	O
a	O
tree	B-Application
data	I-Application
structure	I-Application
consisting	O
of	O
blocks	O
(	O
the	O
root	O
block	O
is	O
implicit	O
,	O
subblocks	O
are	O
delimited	B-Algorithm
by	O
square	O
brackets	O
)	O
,	O
parens	O
(	O
delimited	B-Algorithm
by	O
round	O
brackets	O
)	O
,	O
strings	O
(	O
delimited	B-Algorithm
by	O
double	O
quotes	O
or	O
curly	O
brackets	O
suitable	O
for	O
multi-line	O
strings	O
;	O
caret	O
notation	O
is	O
used	O
for	O
unprintable	O
characters	B-General_Concept
)	O
,	O
URLs	O
,	O
e-mail	O
addresses	O
,	O
files	O
,	O
paths	O
or	O
other	O
composite	O
values	O
.	O
</s>
<s>
Unlike	O
ALGOL	B-Language
blocks	O
,	O
Rebol	B-Application
blocks	O
are	O
composite	O
values	O
similar	O
to	O
quoted	O
s-expressions	B-Protocol
in	O
Lisp	B-Language
.	O
</s>
<s>
The	O
fact	O
that	O
code	O
is	O
written	O
in	O
the	O
form	O
of	O
Rebol	B-Application
blocks	O
makes	O
the	O
language	O
homoiconic	O
.	O
</s>
<s>
Blocks	O
as	O
well	O
as	O
parens	O
may	O
contain	O
other	O
composite	O
values	O
(	O
a	O
block	O
may	O
contain	O
subblocks	O
,	O
parens	O
,	O
strings	O
,	O
...	O
)	O
or	O
scalar	O
values	O
like	O
words	O
,	O
set-words	O
(	O
words	O
suffixed	O
by	O
the	O
colon	O
)	O
,	O
get-words	O
(	O
words	O
prefixed	O
by	O
the	O
colon	O
)	O
,	O
lit-words	O
(	O
words	O
prefixed	O
by	O
the	O
apostrophe	O
)	O
,	O
numbers	O
,	O
money	O
,	O
characters	B-General_Concept
,	O
etc.	O
,	O
separated	O
by	O
whitespace	O
.	O
</s>
<s>
Note	O
that	O
special	O
characters	B-General_Concept
are	O
allowed	O
in	O
words	O
,	O
so	O
a+b	O
is	O
a	O
word	O
unlike	O
a	O
+	O
b	O
,	O
which	O
is	O
a	O
sequence	O
of	O
three	O
words	O
separated	O
by	O
spaces	O
.	O
</s>
<s>
Blocks	O
containing	O
domain-specific	B-Language
language	I-Language
can	O
be	O
submitted	O
as	O
arguments	O
to	O
specific	O
evaluator	B-Application
functions	O
.	O
</s>
<s>
The	O
most	O
frequently	O
used	O
evaluator	B-Application
is	O
the	O
do	O
function	O
.	O
</s>
<s>
It	O
is	O
used	O
by	O
default	O
to	O
interpret	O
the	O
text	O
input	O
to	O
the	O
interpreter	B-Application
console	B-Application
.	O
</s>
<s>
The	O
do	O
dialect	O
interpreted	B-Application
by	O
the	O
do	O
function	O
,	O
is	O
an	O
expression-oriented	O
sublanguage	O
of	O
the	O
data	O
exchange	O
dialect	O
.	O
</s>
<s>
In	O
contrast	O
to	O
imperative	B-Application
programming	I-Application
languages	I-Application
descending	O
from	O
ALGOL	B-Language
,	O
the	O
do	O
dialect	O
has	O
neither	O
keywords	O
,	O
nor	O
statements	O
.	O
</s>
<s>
While	O
not	O
having	O
statements	O
,	O
assignment	O
,	O
together	O
with	O
functions	O
with	O
side-effects	O
can	O
be	O
used	O
for	O
imperative	B-Application
programming	I-Application
.	O
</s>
<s>
This	O
property	O
is	O
used	O
to	O
handle	O
data	O
blocks	O
,	O
for	O
structured	B-Language
programming	I-Language
by	O
submitting	O
blocks	O
as	O
arguments	O
to	O
control	O
functions	O
like	O
if	O
,	O
either	O
,	O
loop	O
,	O
etc.	O
,	O
and	O
for	O
dialecting	O
,	O
when	O
a	O
block	O
is	O
passed	O
to	O
a	O
specific	O
interpreter	B-Application
function	O
.	O
</s>
<s>
first	O
reads	O
the	O
Wikipedia	O
Rebol	B-Application
page	O
and	O
then	O
passes	O
the	O
result	O
to	O
the	O
print	O
function	O
.	O
</s>
<s>
At	O
the	O
string	O
parsing	O
level	O
parse	O
must	O
handle	O
the	O
"	O
low	O
level	O
"	O
parsing	O
,	O
taking	O
into	O
account	O
characters	B-General_Concept
and	O
delimiters	B-Algorithm
.	O
</s>
<s>
Block	O
parsing	O
is	O
higher	O
level	O
,	O
handling	O
the	O
scanning	O
at	O
the	O
level	O
of	O
Rebol	B-Application
values	O
.	O
</s>
<s>
The	O
official	O
Rebol	B-Application
2.7.8	O
implementation	O
is	O
available	O
in	O
several	O
editions	O
(	O
/Core	O
,	O
/View	O
,	O
/Command	O
,	O
/SDK	O
and	O
/IOS	O
)	O
.	O
</s>
<s>
Both	O
/Core	O
and	O
/View	O
editions	O
are	O
freely	B-License
redistributable	I-License
software	I-License
.	O
</s>
<s>
Rebol/Core	O
2.7.8	O
,	O
the	O
console	B-Application
edition	O
,	O
is	O
about	O
300KB	O
and	O
Rebol/View	O
2.7.8	O
,	O
the	O
graphical	B-Application
user	I-Application
interface	I-Application
edition	O
,	O
is	O
about	O
650KB	O
in	O
size	O
.	O
</s>
<s>
Rebol/View	O
provides	O
platform-independent	B-Operating_System
graphics	O
and	O
sound	O
access	O
,	O
and	O
comes	O
with	O
its	O
own	O
windowing	O
toolkit	O
and	O
extensible	O
set	O
of	O
styles	O
(	O
GUI	B-Application
widgets	O
)	O
.	O
</s>
<s>
Extended	O
editions	O
,	O
such	O
as	O
Rebol/Command	O
2.7.8	O
or	O
Rebol/SDK	O
2.7.8	O
require	O
a	O
paid	O
license	O
;	O
they	O
add	O
features	O
like	O
ODBC	B-Application
data	O
access	O
,	O
and	O
the	O
option	O
to	O
create	O
standalone	O
executable	O
files	O
.	O
</s>
<s>
Rebol	B-Application
was	O
named	O
by	O
Douglas	O
Crockford	O
as	O
one	O
of	O
the	O
inspirations	O
of	O
JavaScript	B-General_Concept
Object	I-General_Concept
Notation	I-General_Concept
.	O
</s>
<s>
Rebol	B-Application
inspired	O
the	O
open-source	O
Orca	O
project	O
,	O
which	O
is	O
an	O
interpreted	B-Application
Rebol-like	O
language	O
.	O
</s>
<s>
is	O
an	O
interpreted	B-Application
,	O
homoiconic	O
language	O
inspired	O
by	O
and	O
similar	O
to	O
Rebol	B-Application
,	O
which	O
is	O
meant	O
for	O
embedding	O
domain	B-Language
specific	I-Language
languages	I-Language
.	O
</s>
<s>
It	O
is	O
implemented	O
as	O
a	O
C	B-Language
library	O
licensed	O
under	O
the	O
terms	O
of	O
the	O
LGPLv3	O
.	O
</s>
<s>
The	O
Red	B-Language
programming	I-Language
language	I-Language
was	O
directly	O
inspired	O
by	O
Rebol	B-Application
,	O
yet	O
the	O
implementation	O
choices	O
of	O
Red	B-Language
were	O
geared	O
specifically	O
to	O
overcoming	O
its	O
perceived	O
limitations	O
.	O
</s>
