<s>
Lucid	B-Language
is	O
a	O
dataflow	B-Application
programming	I-Application
language	I-Application
designed	O
to	O
experiment	O
with	O
non-von	O
Neumann	O
programming	O
models	O
.	O
</s>
<s>
It	O
was	O
designed	O
by	O
Bill	O
Wadge	O
and	O
Ed	O
Ashcroft	O
and	O
described	O
in	O
the	O
1985	O
book	O
Lucid	B-Language
,	O
the	O
Dataflow	B-Application
Programming	I-Application
Language	I-Application
.	O
</s>
<s>
pLucid	O
was	O
the	O
first	O
interpreter	B-Application
for	O
Lucid	B-Language
.	O
</s>
<s>
Lucid	B-Language
uses	O
a	O
demand-driven	O
model	O
for	O
data	O
computation	O
.	O
</s>
<s>
Each	O
statement	O
can	O
be	O
understood	O
as	O
an	O
equation	O
defining	O
a	O
network	O
of	O
processors	O
and	O
communication	O
lines	O
between	O
them	O
through	O
which	O
data	B-Application
flows	I-Application
.	O
</s>
<s>
Iteration	B-Algorithm
is	O
simulated	O
by	O
'	O
current	O
 '	O
values	O
and	O
'	O
fby	O
 '	O
(	O
read	O
as	O
'	O
followed	O
by	O
 '	O
)	O
operator	O
allowing	O
composition	O
of	O
streams	O
.	O
</s>
<s>
Lucid	B-Language
is	O
based	O
on	O
an	O
algebra	O
of	O
histories	O
,	O
a	O
history	O
being	O
an	O
infinite	O
sequence	O
of	O
data	O
items	O
.	O
</s>
<s>
Lucid	B-Language
was	O
originally	O
conceived	O
as	O
a	O
disciplined	O
,	O
mathematically	O
pure	O
,	O
single-assignment	O
language	O
,	O
in	O
which	O
verification	O
would	O
be	O
simplified	O
.	O
</s>
<s>
However	O
,	O
the	O
dataflow	B-Application
interpretation	O
has	O
been	O
an	O
important	O
influence	O
on	O
the	O
direction	O
in	O
which	O
Lucid	B-Language
has	O
evolved	O
.	O
</s>
<s>
In	O
Lucid	B-Language
(	O
and	O
other	O
dataflow	B-Application
languages	I-Application
)	O
an	O
expression	O
that	O
contains	O
a	O
variable	O
that	O
has	O
not	O
yet	O
been	O
bound	O
waits	O
until	O
the	O
variable	O
has	O
been	O
bound	O
,	O
before	O
proceeding	O
.	O
</s>
<s>
Each	O
variable	O
in	O
Lucid	B-Language
is	O
a	O
stream	O
of	O
values	O
.	O
</s>
<s>
prime	O
=	O
2	O
fby	O
(	O
n	O
whenever	O
isprime(n )	O
)	O
;	O
</s>
