<s>
Esterel	B-Language
is	O
a	O
synchronous	B-Language
programming	I-Language
language	I-Language
for	O
the	O
development	O
of	O
complex	O
reactive	O
systems	O
.	O
</s>
<s>
The	O
imperative	B-Application
programming	I-Application
style	O
of	O
Esterel	B-Language
allows	O
the	O
simple	O
expression	O
of	O
parallelism	B-Operating_System
and	O
preemption	B-Operating_System
.	O
</s>
<s>
Current	O
compilers	O
take	O
Esterel	B-Language
programs	O
and	O
generate	O
C	B-Language
code	I-Language
or	O
hardware	O
(	O
RTL	O
)	O
implementations	O
(	O
VHDL	B-Language
or	O
Verilog	B-Language
)	O
.	O
</s>
<s>
The	O
commercial	O
version	O
of	O
Esterel	B-Language
is	O
the	O
development	O
environment	O
Esterel	B-Language
Studio	O
.	O
</s>
<s>
The	O
notion	O
of	O
time	O
used	O
in	O
Esterel	B-Language
differs	O
from	O
that	O
of	O
non-synchronous	O
languages	O
in	O
the	O
following	O
way	O
:	O
The	O
notion	O
of	O
physical	O
time	O
is	O
replaced	O
with	O
the	O
notion	O
of	O
order	O
.	O
</s>
<s>
An	O
Esterel	B-Language
program	O
describes	O
a	O
totally	O
ordered	O
sequence	O
of	O
logical	O
instants	O
.	O
</s>
<s>
A	O
signal	B-Application
has	O
the	O
property	O
of	O
being	O
either	O
present	O
or	O
absent	O
in	O
an	O
instant	O
.	O
</s>
<s>
Signals	O
are	O
broadcast	O
across	O
the	O
program	O
,	O
and	O
that	O
means	O
any	O
process	O
can	O
read	O
or	O
write	O
a	O
signal	B-Application
.	O
</s>
<s>
The	O
value	O
of	O
a	O
valued	O
signal	B-Application
can	O
be	O
determined	O
in	O
any	O
instant	O
,	O
even	O
if	O
the	O
signal	B-Application
is	O
absent	O
.	O
</s>
<s>
The	O
default	O
status	O
of	O
a	O
signal	B-Application
is	O
absent	O
.	O
</s>
<s>
Communication	O
is	O
instantaneous	O
,	O
that	O
means	O
that	O
a	O
signal	B-Application
emitted	O
in	O
a	O
cycle	O
is	O
visible	O
immediately	O
.	O
</s>
<s>
Each	O
signal	B-Application
is	O
only	O
present	O
or	O
absent	O
in	O
a	O
cycle	O
,	O
never	O
both	O
.	O
</s>
<s>
is	O
an	O
erroneous	B-Language
program	I-Language
:	O
the	O
writer	O
"	O
emit	O
A	O
"	O
must	O
run	O
before	O
the	O
reader	O
"	O
present	O
A	O
"	O
,	O
but	O
this	O
program	O
asks	O
the	O
"	O
present	O
A	O
"	O
to	O
be	O
performed	O
first	O
.	O
</s>
<s>
Pure	O
Esterel	B-Language
has	O
eleven	O
primitive	O
statements	O
.	O
</s>
<s>
signal	B-Application
S	O
in	O
p	O
end	O
Declares	O
a	O
local	O
signal	B-Application
.	O
</s>
<s>
emit	O
S	O
Make	O
signal	B-Application
S	O
present	O
in	O
the	O
current	O
instant	O
.	O
</s>
<s>
A	O
signal	B-Application
is	O
absent	O
unless	O
it	O
is	O
emitted	O
.	O
</s>
<s>
present	O
S	O
then	O
p	O
else	O
q	O
end	O
If	O
signal	B-Application
S	O
is	O
present	O
in	O
the	O
current	O
instant	O
,	O
immediately	O
run	O
p	O
,	O
otherwise	O
run	O
q	O
.	O
suspend	O
p	O
when	O
S	O
Suspends	O
the	O
execution	O
of	O
the	O
body	O
in	O
instants	O
where	O
S	O
is	O
present	O
.	O
</s>
<s>
Esterel	B-Language
has	O
several	O
derived	O
constructions	O
:	O
</s>
<s>
The	O
full	O
Esterel	B-Language
language	I-Language
also	O
has	O
statements	O
for	O
declaring	O
and	O
instantiating	O
modules	O
,	O
for	O
variables	O
,	O
for	O
calling	O
external	O
procedures	O
,	O
and	O
for	O
valued	O
signals	O
.	O
</s>
