<s>
Action	B-Language
!	I-Language
</s>
<s>
is	O
a	O
procedural	O
programming	O
language	O
and	O
integrated	B-Application
development	I-Application
environment	I-Application
written	O
by	O
Clinton	O
Parker	O
for	O
the	O
Atari	B-Device
8-bit	I-Device
family	I-Device
.	O
</s>
<s>
The	O
language	O
,	O
which	O
is	O
similar	O
to	O
ALGOL	B-Language
,	O
compiles	O
to	O
high-performance	O
code	O
for	O
the	O
MOS	B-General_Concept
Technologies	I-General_Concept
6502	I-General_Concept
of	O
the	O
Atari	O
computers	O
.	O
</s>
<s>
Action	B-Language
!	I-Language
</s>
<s>
was	O
distributed	O
on	O
ROM	B-Protocol
cartridge	I-Protocol
by	O
Optimized	B-Operating_System
Systems	I-Operating_System
Software	I-Operating_System
starting	O
in	O
1983	O
.	O
</s>
<s>
It	O
was	O
one	O
of	O
the	O
company	O
's	O
first	O
bank-switched	B-General_Concept
16kB	O
"	O
Super	O
Cartridges	B-Protocol
"	O
.	O
</s>
<s>
The	O
runtime	O
library	O
is	O
stored	O
in	O
the	O
cartridge	B-Protocol
;	O
to	O
make	O
a	O
standalone	O
application	O
requires	O
the	O
Action	B-Language
!	I-Language
</s>
<s>
Parker	O
,	O
working	O
with	O
Henry	O
Baker	O
,	O
had	O
previously	O
developed	O
Micro-SPL	O
,	O
a	O
systems	B-Language
programming	I-Language
language	I-Language
for	O
the	O
Xerox	B-Device
Alto	I-Device
.	O
</s>
<s>
Action	B-Language
!	I-Language
</s>
<s>
is	O
largely	O
a	O
port	O
of	O
Micro-SPL	O
concepts	O
to	O
the	O
Atari	O
with	O
changes	O
to	O
support	O
the	O
6502	B-General_Concept
processor	I-General_Concept
and	O
the	O
addition	O
of	O
an	O
integrated	O
fullscreen	O
editor	O
and	O
debugger	O
.	O
</s>
<s>
Action	B-Language
!	I-Language
</s>
<s>
was	O
used	O
to	O
develop	O
at	O
least	O
two	O
commercial	O
products	O
—	O
the	O
HomePak	B-Protocol
productivity	O
suite	O
and	O
Games	O
Computers	O
Play	O
client	O
program	O
—	O
and	O
numerous	O
programs	O
in	O
ANALOG	O
Computing	O
and	O
Antic	B-General_Concept
magazines	O
.	O
</s>
<s>
The	O
editor	O
inspired	O
the	O
PaperClip	B-Protocol
word	B-General_Concept
processor	I-General_Concept
.	O
</s>
<s>
The	O
assembly	O
language	O
source	O
code	O
for	O
Action	B-Language
!	I-Language
</s>
<s>
was	O
made	O
available	O
under	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
by	O
the	O
author	O
in	O
2015	O
.	O
</s>
<s>
Action	B-Language
!	I-Language
</s>
<s>
ROM	B-Protocol
cartridges	I-Protocol
on	O
the	O
Atari	O
were	O
normally	O
limited	O
to	O
8kB	O
,	O
which	O
limited	O
its	O
ability	O
to	O
support	O
larger	O
programs	O
.	O
</s>
<s>
The	O
lower	O
4kB	O
did	O
not	O
change	O
,	O
and	O
system	O
could	O
bank	B-General_Concept
switch	I-General_Concept
between	O
the	O
other	O
three	O
blocks	O
by	O
changing	O
the	O
value	O
in	O
address	O
$AFFF	O
.	O
</s>
<s>
Action	B-Language
!	I-Language
</s>
<s>
used	O
this	O
design	O
by	O
breaking	O
the	O
system	O
into	O
four	O
sections	O
,	O
the	O
editor	O
,	O
the	O
compiler	O
,	O
a	O
monitor	B-General_Concept
for	O
testing	O
code	O
and	O
switching	O
between	O
the	O
editor	O
and	O
compiler	O
,	O
and	O
the	O
run-time	O
library	O
.	O
</s>
<s>
The	O
run-time	O
library	O
is	O
stored	O
in	O
the	O
cartridge	B-Protocol
itself	O
.	O
</s>
<s>
To	O
distribute	O
standalone	O
applications	O
requires	O
a	O
separate	O
run-time	O
package	O
which	O
was	O
sold	O
by	O
OSS	O
as	O
the	O
Action	B-Language
!	I-Language
</s>
<s>
Action	B-Language
!	I-Language
</s>
<s>
constructs	O
were	O
designed	O
to	O
map	O
cleanly	O
to	O
6502	B-General_Concept
opcodes	B-Language
,	O
to	O
provide	O
high	O
performance	O
without	O
needing	O
complex	O
optimizations	O
in	O
the	O
one-pass	B-Language
compiler	I-Language
.	O
</s>
<s>
This	O
eliminates	O
the	O
significant	O
overhead	O
associated	O
with	O
stack	O
management	O
,	O
which	O
is	O
especially	O
difficult	O
in	O
the	O
case	O
of	O
the	O
6502	B-General_Concept
's	O
256-byte	O
stack	O
.	O
</s>
<s>
Unlike	O
the	O
integrated	O
Atari	B-Language
BASIC	I-Language
and	O
Atari	B-Application
Assembler	I-Application
Editor	I-Application
environments	O
,	O
the	O
Action	B-Language
!	I-Language
</s>
<s>
The	O
monitor	B-General_Concept
serves	O
as	O
a	O
debugger	O
,	O
allowing	O
an	O
entire	O
program	O
or	O
individual	O
functions	O
to	O
be	O
run	O
,	O
memory	O
to	O
be	O
displayed	O
and	O
modified	O
,	O
and	O
program	O
execution	O
to	O
be	O
traced	O
.	O
</s>
<s>
Action	B-Language
!	I-Language
</s>
<s>
has	O
three	O
fundamental	O
data	O
types	O
,	O
all	O
of	O
which	O
are	O
numeric	B-Algorithm
.	O
</s>
<s>
BYTE	B-Application
is	O
internally	O
represented	O
as	O
an	O
unsigned	B-Algorithm
8-bit	O
integer	O
.	O
</s>
<s>
The	O
CHAR	O
keyword	O
can	O
also	O
be	O
used	O
to	O
declare	O
BYTE	B-Application
variables	O
.	O
</s>
<s>
CARDinal	O
is	O
internally	O
represented	O
as	O
an	O
unsigned	B-Algorithm
16-bit	O
integer	O
.	O
</s>
<s>
INTeger	O
is	O
internally	O
represented	O
as	O
a	O
signed	B-Algorithm
16-bit	O
integer	O
.	O
</s>
<s>
Action	B-Language
!	I-Language
</s>
<s>
No	O
floating	B-Algorithm
point	I-Algorithm
support	O
is	O
provided	O
.	O
</s>
<s>
A	O
reserved	O
word	O
is	O
any	O
identifier	O
or	O
symbol	O
that	O
the	O
Action	B-Language
!	I-Language
</s>
<s>
BYTE	B-Application
FUNC	O
PROC	O
XOR	O
#	O
.	O
</s>
<s>
The	O
following	O
is	O
example	O
code	O
for	O
Sieve	B-Algorithm
of	I-Algorithm
Eratosthenes	I-Algorithm
written	O
in	O
Action	B-Language
!	I-Language
.	O
</s>
<s>
In	O
order	O
to	O
increase	O
performance	O
,	O
it	O
disables	O
the	O
ANTIC	B-General_Concept
graphics	O
coprocessor	O
,	O
preventing	O
its	O
DMA	B-General_Concept
engine	I-General_Concept
from	O
"	O
stealing	O
"	O
CPU	O
cycles	O
during	O
computation	O
.	O
</s>
<s>
While	O
taking	O
his	O
postgraduate	O
studies	O
,	O
Parker	O
started	O
working	O
part-time	O
at	O
Xerox	O
PARC	O
working	O
on	O
printer	B-Application
drivers	I-Application
.	O
</s>
<s>
He	O
later	O
moved	O
to	O
the	O
Xerox	B-Device
Alto	I-Device
project	O
where	O
he	O
wrote	O
several	O
games	O
for	O
the	O
system	O
.	O
</s>
<s>
Micro-SPL	O
was	O
intended	O
to	O
be	O
used	O
as	O
a	O
systems	B-Language
programming	I-Language
language	I-Language
on	O
the	O
Xerox	B-Device
Alto	I-Device
workstation	B-Device
computer	I-Device
,	O
which	O
was	O
normally	O
programmed	O
in	O
BCPL	B-Language
.	O
</s>
<s>
The	O
Alto	B-Device
used	O
a	O
microcode	B-Device
system	O
which	O
the	O
BCPL	B-Language
compiler	O
output	O
.	O
</s>
<s>
Micro-SPL	O
output	O
the	O
same	O
format	O
,	O
allowing	O
BCPL	B-Language
programs	O
to	O
call	O
Micro-SPL	O
programs	O
.	O
</s>
<s>
Aside	O
from	O
differences	O
in	O
syntax	O
,	O
the	O
main	O
difference	O
between	O
Micro-SPL	O
and	O
BCPL	B-Language
,	O
and	O
the	O
reason	O
for	O
its	O
existence	O
,	O
was	O
that	O
Micro-SPL	O
produced	O
code	O
that	O
was	O
many	O
times	O
faster	O
than	O
the	O
native	O
BCPL	B-Language
compiler	O
.	O
</s>
<s>
In	O
general	O
,	O
Micro-SPL	O
programs	O
were	O
expected	O
to	O
run	O
about	O
ten	O
times	O
as	O
fast	O
as	O
BCPL	B-Language
,	O
and	O
about	O
half	O
as	O
fast	O
as	O
good	O
hand-written	O
microcode	B-Device
.	O
</s>
<s>
In	O
comparison	O
to	O
microcode	B-Device
,	O
they	O
claimed	O
it	O
would	O
take	O
half	O
as	O
long	O
to	O
write	O
and	O
10%	O
of	O
the	O
time	O
to	O
debug	O
it	O
.	O
</s>
<s>
This	O
was	O
the	O
impetus	O
for	O
creating	O
Action	B-Language
!	I-Language
</s>
<s>
Parker	O
initially	O
considered	O
releasing	O
the	O
system	O
himself	O
,	O
but	O
later	O
decided	O
to	O
partner	O
with	O
Optimized	B-Operating_System
Systems	I-Operating_System
Software	I-Operating_System
(	O
OSS	O
)	O
for	O
sales	O
and	O
distribution	O
.	O
</s>
<s>
OSS	O
focused	O
on	O
utilities	O
and	O
programming	O
languages	O
like	O
BASIC	O
XL	O
,	O
so	O
this	O
was	O
a	O
natural	O
fit	O
for	O
Action	B-Language
!	I-Language
</s>
<s>
The	O
IBM	B-Device
PC	I-Device
had	O
C	B-Language
compilers	O
available	O
,	O
and	O
Parker	O
decided	O
there	O
was	O
no	O
point	O
in	O
porting	O
Action	B-Language
!	I-Language
</s>
<s>
As	O
the	O
sales	O
of	O
the	O
Atari	B-Device
8-bit	I-Device
computers	I-Device
wound	O
down	O
in	O
North	O
America	O
,	O
OSS	O
wound	O
down	O
as	O
well	O
.	O
</s>
<s>
Late	O
in	O
its	O
history	O
Action	B-Language
!	I-Language
</s>
<s>
Brian	O
Moriarty	O
,	O
in	O
a	O
February	O
1984	O
review	O
for	O
ANALOG	O
Computing	O
,	O
concluded	O
that	O
Action	B-Language
!	I-Language
</s>
<s>
He	O
said	O
that	O
Action	B-Language
!	I-Language
</s>
<s>
ran	O
about	O
200	O
times	O
as	O
fast	O
as	O
Atari	B-Language
BASIC	I-Language
,	O
concluding	O
that	O
"	O
This	O
language	O
is	O
like	O
a	O
finely	O
tuned	O
racing	O
car.	O
"	O
</s>
<s>
BYTE	B-Application
in	O
1985	O
praised	O
the	O
compilation	O
and	O
execution	O
speed	O
of	O
software	O
written	O
in	O
Action	B-Language
!	I-Language
</s>
<s>
Using	O
their	O
Byte	B-Language
Sieve	I-Language
benchmark	O
as	O
a	O
test	O
,	O
ten	O
iterations	O
of	O
the	O
sieve	O
completed	O
in	O
18	O
seconds	O
in	O
Action	O
!,	O
compared	O
to	O
10	O
seconds	O
for	O
assembly	O
and	O
38	O
minutes	O
in	O
BASIC	O
.	O
</s>
<s>
BYTE	B-Application
reported	O
that	O
the	O
language	O
resembled	O
C	B-Language
closely	O
enough	O
to	O
"	O
routinely	O
convert	O
programs	O
between	O
the	O
two	O
"	O
,	O
and	O
approved	O
of	O
its	O
pointer	O
support	O
.	O
</s>
<s>
The	O
magazine	O
concluded	O
that	O
"	O
Action	B-Language
!	I-Language
</s>
<s>
Action	B-Language
!	I-Language
</s>
<s>
Ian	O
Chadwick	O
wrote	O
in	O
Mapping	O
the	O
Atari	O
that	O
"	O
Action	B-Language
!	I-Language
</s>
<s>
is	O
probably	O
the	O
best	O
language	O
yet	O
for	O
the	O
Atari	O
;	O
it	O
's	O
a	O
bit	O
like	O
C	B-Language
and	O
Pascal	O
,	O
with	O
a	O
dash	O
of	O
Forth	O
.	O
</s>
