<s>
It	O
was	O
first	O
implemented	O
as	O
an	O
extension	O
to	O
the	O
Fortran	B-Application
programming	I-Application
language	I-Application
,	O
and	O
later	O
embedded	O
into	O
MAD	B-Language
and	O
ALGOL	B-Language
.	O
</s>
<s>
The	O
best	O
known	O
program	O
written	O
in	O
the	O
language	O
is	O
ELIZA	B-Application
,	O
an	O
early	O
natural	B-Language
language	I-Language
processing	I-Language
computer	B-Application
program	I-Application
created	O
by	O
Weizenbaum	O
at	O
the	O
MIT	O
Artificial	O
Intelligence	O
Laboratory	O
.	O
</s>
<s>
In	O
a	O
nutshell	O
,	O
SLIP	O
consisted	O
of	O
a	O
set	O
of	O
FORTRAN	B-Application
"	O
accessor	O
"	O
functions	O
which	O
operated	O
on	O
circular	B-Data_Structure
doubly	I-Data_Structure
linked	I-Data_Structure
lists	I-Data_Structure
with	O
fixed-size	O
data	O
fields	O
.	O
</s>
<s>
The	O
header	O
included	O
a	O
reference	O
count	O
field	O
for	O
garbage	B-General_Concept
collection	I-General_Concept
purposes	O
.	O
</s>
<s>
The	O
reader	O
was	O
essentially	O
a	O
state	O
history	O
stack	O
—	O
a	O
good	O
example	O
of	O
a	O
memento	B-Language
pattern	I-Language
—	O
where	O
each	O
cell	O
pointed	O
to	O
the	O
header	O
of	O
the	O
list	O
being	O
read	O
,	O
the	O
current	O
position	O
within	O
the	O
list	O
being	O
read	O
,	O
and	O
the	O
level	O
or	O
depth	O
of	O
the	O
history	O
stack	O
.	O
</s>
