<s>
ALGOL	B-General_Concept
68C	I-General_Concept
is	O
an	O
imperative	B-Application
computer	B-General_Concept
programming	I-General_Concept
language	O
,	O
a	O
dialect	O
of	O
ALGOL	B-Language
68	I-Language
,	O
that	O
was	O
developed	O
by	O
Stephen	O
R	O
.	O
Bourne	O
and	O
Michael	O
Guy	O
to	O
program	O
the	O
Cambridge	B-Application
Algebra	I-Application
System	I-Application
(	O
CAMAL	B-Application
)	O
.	O
</s>
<s>
The	O
initial	O
compiler	B-Language
was	O
written	O
in	O
the	O
Princeton	O
Syntax	O
Compiler	B-Language
(	O
PSYCO	O
,	O
by	O
Edgar	O
T	O
.	O
Irons	O
)	O
that	O
was	O
implemented	O
by	O
J	O
.	O
H	O
.	O
Mathewman	O
at	O
Cambridge	O
.	O
</s>
<s>
ALGOL	B-General_Concept
68C	I-General_Concept
was	O
later	O
used	O
for	O
the	O
CHAOS	O
OS	O
for	O
the	O
capability-based	O
security	O
CAP	B-Device
computer	I-Device
at	O
University	O
of	O
Cambridge	O
in	O
1971	O
.	O
</s>
<s>
Subsequent	O
work	O
was	O
done	O
on	O
the	O
compiler	B-Language
after	O
Bourne	O
left	O
Cambridge	O
University	O
in	O
1975	O
.	O
</s>
<s>
Garbage	B-General_Concept
collection	I-General_Concept
was	O
added	O
,	O
and	O
the	O
code	O
base	O
is	O
still	O
running	O
on	O
an	O
emulated	O
OS/MVT	O
using	O
Hercules	B-Application
.	O
</s>
<s>
The	O
ALGOL	B-General_Concept
68C	I-General_Concept
compiler	B-Language
generated	O
output	O
in	O
ZCODE	B-General_Concept
,	O
a	O
register-based	O
intermediate	O
language	O
,	O
which	O
could	O
then	O
be	O
either	O
interpreted	O
or	O
compiled	B-Language
to	O
a	O
native	O
executable	O
.	O
</s>
<s>
This	O
ability	O
to	O
interpret	O
or	O
compile	B-Language
ZCODE	B-General_Concept
encouraged	O
the	O
porting	O
of	O
ALGOL	B-General_Concept
68C	I-General_Concept
to	O
many	O
different	O
computing	B-Device
platforms	I-Device
.	O
</s>
<s>
Aside	O
from	O
the	O
CAP	B-Device
computer	I-Device
,	O
the	O
compiler	B-Language
was	O
ported	O
to	O
systems	O
including	O
Conversational	B-Operating_System
Monitor	I-Operating_System
System	I-Operating_System
(	O
CMS	O
)	O
,	O
TOPS-10	B-Operating_System
,	O
and	O
Zilog	B-General_Concept
Z80	I-General_Concept
.	O
</s>
<s>
A	O
very	O
early	O
predecessor	O
of	O
this	O
compiler	B-Language
was	O
used	O
by	O
Guy	O
and	O
Bourne	O
to	O
write	O
the	O
first	O
Game	O
of	O
Life	O
programs	O
on	O
the	O
PDP-7	B-Device
with	O
a	O
DEC	O
340	O
display	O
.	O
</s>
<s>
Various	O
Liverpool	O
Software	O
Gazette	O
issues	O
detail	O
the	O
Z80	B-General_Concept
implementation	O
.	O
</s>
<s>
The	O
compiler	B-Language
required	O
about	O
120	O
KB	O
of	O
memory	O
to	O
run	O
;	O
hence	O
the	O
Z80	B-General_Concept
's	O
64	O
KB	O
memory	O
is	O
actually	O
too	O
small	O
to	O
run	O
the	O
compiler	B-Language
.	O
</s>
<s>
So	O
ALGOL	B-General_Concept
68C	I-General_Concept
programs	O
for	O
the	O
Z80	B-General_Concept
had	O
to	O
be	O
cross-compiled	B-Application
from	O
the	O
larger	O
CAP	B-Device
computer	I-Device
,	O
or	O
an	O
IBM	B-Device
System/370	I-Device
mainframe	B-Architecture
computer	I-Architecture
.	O
</s>
<s>
Stephen	O
Bourne	O
subsequently	O
reused	O
ALGOL	B-Language
68	I-Language
's	O
if	O
~	O
then	O
~	O
else	O
~	O
fi	O
,	O
case	O
~	O
in	O
~	O
out	O
~	O
esac	O
and	O
for	O
~	O
while	O
~	O
do	O
~	O
od	B-Device
clauses	O
in	O
the	O
common	O
Unix	B-Application
Bourne	B-Device
shell	I-Device
,	O
but	O
with	O
in	O
's	O
syntax	O
changed	O
,	O
out	O
removed	O
,	O
and	O
od	B-Device
replaced	O
with	O
done	O
(	O
to	O
avoid	O
conflict	O
with	O
the	O
od	B-Device
utility	O
)	O
.	O
</s>
<s>
After	O
Cambridge	O
,	O
Bourne	O
spent	O
nine	O
years	O
at	O
Bell	O
Labs	O
with	O
the	O
Version	B-Operating_System
7	I-Operating_System
Unix	I-Operating_System
(	O
Seventh	B-Operating_System
Edition	I-Operating_System
Unix	I-Operating_System
)	O
team	O
.	O
</s>
<s>
As	O
well	O
as	O
developing	O
the	B-Device
Bourne	I-Device
shell	I-Device
,	O
he	O
ported	O
ALGOL	B-General_Concept
68C	I-General_Concept
to	O
Unix	B-Application
on	O
the	O
DEC	O
PDP-11-45	O
and	O
included	O
a	O
special	O
option	O
in	O
his	O
Unix	B-Application
debugger	B-Application
Advanced	B-Application
Debugger	I-Application
(	O
adb	O
)	O
to	O
obtain	O
a	O
stack	O
backtrace	O
for	O
programs	O
written	O
in	O
ALGOL	B-General_Concept
68C	I-General_Concept
.	O
</s>
<s>
Here	O
is	O
an	O
extract	O
from	O
the	O
Unix	B-Operating_System
7th	I-Operating_System
edition	I-Operating_System
manual	O
pages	O
:	O
</s>
<s>
a	O
ALGOL	B-Language
68	I-Language
stack	O
backtrace	O
.	O
</s>
<s>
Separate	O
compilation	B-Language
in	O
ALGOL	B-General_Concept
68C	I-General_Concept
is	O
done	O
using	O
the	O
ENVIRON	O
and	O
USING	O
clauses	O
.	O
</s>
<s>
These	O
clauses	O
are	O
kind	O
of	O
the	O
inverse	O
of	O
the	O
#include	O
found	O
in	O
the	O
C	B-Language
programming	I-Language
language	I-Language
,	O
or	O
import	O
found	O
in	O
Python	B-Language
.	O
</s>
<s>
It	O
is	O
only	O
necessary	O
to	O
parse	O
the	O
shared	O
source	O
file	O
once	O
,	O
unlike	O
a	O
#include	O
found	O
in	O
the	O
C	B-Language
programming	I-Language
language	I-Language
where	O
the	O
include	O
file	O
needs	O
to	O
be	O
parsed	O
for	O
each	O
source	O
file	O
that	O
includes	O
it	O
.	O
</s>
<s>
A	O
translator	B-Application
–	O
compiler	B-Language
for	O
ALGOL	B-General_Concept
68C	I-General_Concept
was	O
available	O
for	O
the	O
PDP-10	B-Device
,	O
IBM	B-Application
System/360	I-Application
and	O
several	O
other	O
computers	O
.	O
</s>
