<s>
E	B-Language
is	O
an	O
object-oriented	B-Language
programming	I-Language
language	I-Language
for	O
secure	O
distributed	B-Architecture
computing	I-Architecture
,	O
created	O
by	O
Mark	O
S	O
.	O
Miller	O
,	O
Dan	B-Application
Bornstein	I-Application
,	O
Douglas	O
Crockford	O
,	O
Chip	O
Morningstar	O
and	O
others	O
at	O
Electric	O
Communities	O
in	O
1997	O
.	O
</s>
<s>
E	B-Language
is	O
mainly	O
descended	O
from	O
the	O
concurrent	O
language	O
Joule	B-Language
and	O
from	O
Original-E	O
,	O
a	O
set	O
of	O
extensions	O
to	O
Java	B-Language
for	O
secure	O
distributed	B-Architecture
programming	I-Architecture
.	O
</s>
<s>
E	B-Language
combines	O
message-based	B-Architecture
computation	O
with	O
Java-like	O
syntax	O
.	O
</s>
<s>
A	O
concurrency	B-Architecture
model	O
based	O
on	O
event	B-Application
loops	I-Application
and	O
promises	B-Operating_System
ensures	O
that	O
deadlock	B-Operating_System
can	O
never	O
occur	O
.	O
</s>
<s>
The	O
E	B-Language
language	O
is	O
designed	O
for	O
computer	O
security	O
and	O
secure	O
computing	O
.	O
</s>
<s>
This	O
is	O
performed	O
mainly	O
by	O
strict	O
adherence	O
to	O
the	O
object-oriented	B-Language
computing	I-Language
model	O
,	O
which	O
in	O
its	O
pure	O
form	O
,	O
has	O
properties	O
that	O
support	O
secure	O
computing	O
.	O
</s>
<s>
The	O
E	B-Language
language	O
and	O
its	O
standard	O
library	B-Library
employ	O
a	O
capability-based	O
design	O
philosophy	O
throughout	O
in	O
order	O
to	O
help	O
programmers	O
build	O
secure	O
software	O
and	O
to	O
enable	O
software	O
components	O
to	O
co-operate	O
even	O
if	O
they	O
do	O
n't	O
fully	O
trust	O
each	O
other	O
.	O
</s>
<s>
In	O
E	B-Language
,	O
object	O
references	O
serve	O
as	O
capabilities	O
,	O
hence	O
capabilities	O
add	O
no	O
computational	O
or	O
conceptual	O
overhead	O
costs	O
.	O
</s>
<s>
For	O
example	O
,	O
lexical	O
scoping	B-Language
limits	O
the	O
amount	O
of	O
code	O
that	O
must	O
be	O
examined	O
for	O
its	O
effects	O
on	O
a	O
given	O
variable	O
.	O
</s>
<s>
In	O
E	B-Language
,	O
all	O
values	O
are	O
objects	B-Language
and	O
computation	O
is	O
performed	O
by	O
sending	O
messages	O
to	O
objects	B-Language
.	O
</s>
<s>
Each	O
object	O
belongs	O
to	O
a	O
vat	O
(	O
analogous	O
to	O
a	O
process	B-Operating_System
)	O
.	O
</s>
<s>
Distributed	B-Architecture
programming	I-Architecture
is	O
just	O
a	O
matter	O
of	O
sending	O
messages	O
to	O
remote	O
objects	B-Language
(	O
objects	B-Language
in	O
other	O
vats	O
)	O
.	O
</s>
<s>
All	O
communication	O
with	O
remote	O
parties	O
is	O
encrypted	O
by	O
the	O
E	B-Language
runtime	O
.	O
</s>
<s>
E	B-Language
has	O
two	O
ways	O
to	O
send	O
messages	O
:	O
an	O
immediate	O
call	O
and	O
an	O
eventual	O
send	O
.	O
</s>
<s>
An	O
eventual	O
send	O
sends	O
a	O
message	O
while	O
producing	O
a	O
placeholder	O
for	O
a	O
result	O
called	O
a	O
promise	B-Operating_System
.	O
</s>
<s>
A	O
sender	O
proceeds	O
immediately	O
with	O
the	O
promise	B-Operating_System
.	O
</s>
<s>
Later	O
,	O
when	O
a	O
receiver	O
finishes	O
and	O
yields	O
a	O
result	O
,	O
the	O
promise	B-Operating_System
resolves	O
to	O
a	O
result	O
.	O
</s>
<s>
Since	O
only	O
eventual	O
sends	O
are	O
allowed	O
when	O
communicating	O
with	O
remote	O
objects	B-Language
,	O
deadlocks	B-Operating_System
cannot	O
happen	O
.	O
</s>
<s>
In	O
distributed	B-Architecture
systems	I-Architecture
,	O
the	O
promise	B-Operating_System
mechanism	O
also	O
minimizes	O
delays	O
caused	O
by	O
network	O
latency	O
.	O
</s>
<s>
E	B-Language
's	O
syntax	O
is	O
most	O
similar	O
to	O
Java	B-Language
,	O
though	O
it	O
also	O
bears	O
some	O
resemblance	O
to	O
Python	B-Language
and	O
Pascal	B-Application
.	O
</s>
<s>
Variables	O
are	O
dynamically	O
typed	O
and	O
lexically	O
scoped	B-Language
.	O
</s>
<s>
Unlike	O
Java	B-Language
or	O
Python	B-Language
,	O
however	O
,	O
E	B-Language
is	O
composed	O
entirely	O
of	O
expressions	O
.	O
</s>
<s>
Here	O
is	O
an	O
extremely	O
simple	O
E	B-Language
program	O
:	O
</s>
<s>
Here	O
is	O
a	O
recursive	O
function	O
for	O
computing	O
the	O
factorial	O
of	O
a	O
number	O
,	O
written	O
in	O
E	B-Language
.	O
Functions	O
are	O
defined	O
using	O
the	O
keyword	O
.	O
</s>
<s>
Since	O
E	B-Language
is	O
intended	O
to	O
support	O
secure	O
co-operation	O
,	O
the	O
canonical	O
example	O
for	O
E	B-Language
programs	O
is	O
the	O
mint	O
,	O
a	O
simple	O
electronic	O
money	O
system	O
in	O
just	O
a	O
few	O
lines	O
of	O
E	B-Language
.	O
The	O
following	O
code	O
defines	O
a	O
function	O
that	O
makes	O
mints	O
,	O
where	O
each	O
mint	O
has	O
its	O
own	O
currency	O
.	O
</s>
<s>
By	O
quick	O
examination	O
of	O
the	O
source	O
code	O
,	O
an	O
E	B-Language
programmer	O
can	O
easily	O
verify	O
that	O
only	O
mints	O
may	O
change	O
the	O
amount	O
of	O
money	O
in	O
circulation	O
,	O
that	O
money	O
can	O
only	O
be	O
created	O
and	O
not	O
destroyed	O
,	O
that	O
mints	O
can	O
only	O
create	O
money	O
of	O
their	O
own	O
currency	O
,	O
and	O
that	O
only	O
the	O
holder	O
of	O
a	O
purse	O
can	O
change	O
its	O
balance	O
.	O
</s>
<s>
Objects	B-Language
in	O
E	B-Language
are	O
defined	O
with	O
the	O
keyword	O
,	O
and	O
within	O
the	O
object	O
definition	O
,	O
the	O
keyword	O
begins	O
each	O
method	O
.	O
</s>
<s>
The	O
function	O
creates	O
two	O
associated	O
objects	B-Language
,	O
a	O
sealer	O
and	O
an	O
unsealer	O
,	O
such	O
that	O
the	O
sealer	O
can	O
seal	O
an	O
object	O
in	O
a	O
box	O
and	O
the	O
unsealer	O
is	O
the	O
only	O
object	O
that	O
can	O
retrieve	O
the	O
contents	O
of	O
the	O
box	O
.	O
</s>
<s>
See	O
the	O
E	B-Language
website	O
for	O
a	O
more	O
detailed	O
explanation	O
of	O
this	O
money	O
example	O
.	O
</s>
