Action! (programming language)

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Action! editor
Action! editor
Original author(s)Clinton Parker[1]
Developer(s)Optimized Systems Software
Final release
v3.6 / 1983; 36 years ago (1983)
PlatformAtari 8-bit family
Size16K bank-switched cartridge

Action! is a procedural programming language similar to ALGOL 68 that is intended to produce high-performance programs for the Atari 8-bit family. The language was written by Clinton Parker and distributed on ROM cartridge by Optimized Systems Software starting in 1983.

Action! was used to develop at least two commercial products—the Homepak productivity suite and Games Computers Play client program—and numerous programs in ANALOG Computing and Antic magazines. The system was not ported to any other platforms.

Parker had previously developed Micro-SPL with Henry Baker, a similar programming language for the Xerox Alto.[2] The 6502 assembly language source code for Action! was made available under the GNU General Public License by the author in 2015.[3]

Development environment[edit]

Action! consists of the editor, the compiler, a monitor for testing code and switching between the editor and compiler, and the run-time library.[4] The run-time library is stored in the cartridge itself. To distribute standalone applications requires a separate run-time package[4] which was sold by OSS as the Action! Toolkit.

Action! constructs were designed to map cleanly to 6502 opcodes, to provide high performance without needing complex optimizations in the one-pass compiler.[5] For example, local variables are assigned fixed addresses in memory, instead of being allocated on the stack. This enables tight code for the 6502, but precludes the use of recursion.

Unlike the integrated Atari BASIC and Atari Assembler Editor environments, the Action! editor is full-screen, so it does not use line numbers. It features a full-screen, scrolling display capable of displaying two windows, as well as block operations and global search and replace.

The monitor serves as a debugger, allowing an entire program or individual functions to be run, memory to be displayed and modified, and program execution to be traced.[4]

Data types[edit]

Action! has three fundamental data types, all of which are numeric.


Internally represented as an unsigned 8-bit integer. Values range from 0 to 255.
The CHAR keyword can also be used to declare BYTE variables.

 BYTE age=[21]      ; declare age and initialize it to the value 21
 BYTE leftMargin=82 ; declare leftMargin at address 82


Internally represented as an unsigned 16-bit integer. Values range from 0 to 65,535.

 CARD population=$600             ; declare population and store it at address 1536 and 1537
 CARD prevYear, curYear, nextYear ; use commas to declare multiple variables


Internally represented as a signed 16-bit integer. Values range from -32,768 to 32,767.

 INT veryCold = [-10]
 INT profitsQ1, profitsQ2,  ; declaring multiple variables can 
     profitsQ3, profitsQ4   ; span across multiple lines

Action! also has ARRAYs, POINTERs and user-defined TYPEs. No floating point support is provided.

An example of a user-defined TYPE:

 CORD point

Reserved words[edit]

A reserved word is any identifier or symbol that the Action! compiler recognizes as something special. It can be an operator, a data type name, a statement, or a compiler directive.

 AND       FI         OR         UNTIL    =     (
 ARRAY     FOR        POINTER    WHILE    <>    )
 BYTE      FUNC       PROC       XOR      #     .
 CARD      IF         RETURN     +        >     [
 CHAR      INCLUDE    RSH        -        >=    ]
 DEFINE    INT        SET        *        <     "
 DO        LSH        STEP       /        <=    '
 ELSE      MOD        THEN       &        $     ;
 ELSEIF    MODULE     TO         %        ^
 EXIT      OD         TYPE       !        @

Example code[edit]

The following is example code for Sieve of Eratosthenes written in Action!. In order to increase performance, it disables the ANTIC graphics co-processor, preventing its DMA engine from "stealing" CPU cycles during computation.

BYTE RTCLOK=20, ; addr of sys timer
     SDMCTL=559 ; DMA control




  SDMCTL=0 ; shut off Antic
  RTCLOK=0 ; reset the clock to zero

  COUNT=0         ; init count
  FOR I=0 TO 8190 ; and flags
    FLAGS(I)='T ; "'T" is a compiler-provided constant for True

  FOR I=0 TO 8190 ; and flags
      WHILE K<=8190
        FLAGS(K)='F ; "'F" is a compiler-provided constant for False
  TIME=RTCLOK ; get timer reading
  SDMCTL=34   ; restore screen



Brian Moriarty, in a February 1984 review for ANALOG Computing, cited the manual as the weak point of the package: "[it] suffers from lack of confidence, uncertain organization and a shortage of good, hard technical data." He concluded by calling Action! "one of the most valuable development tools ever published for the Atari."[4]

BYTE in 1985 praised the compilation and execution speed of software written in Action!—ten iterations of the Sieve of Eratosthenes ran in less than 18 seconds, compared to 10 seconds for assembly and 38 minutes in BASIC—and its editor. The magazine reported that the language resembled C closely enough to "routinely convert programs between the two", and approved of its pointer support. BYTE concluded that "Action! is easy to use, quick, and efficient. It can exploit the Atari's full power. Action! puts programming for the Atari in a whole new dimension."[6]

Ian Chadwick wrote in Mapping the Atari that "Action! is probably the best language yet for the Atari; it's a bit like C and Pascal, with a dash of Forth. I recommend it."[7]

See also[edit]

  • PaperClip, Atari 8-bit word processor from a different author and company, based on the Action! editor


  1. ^ Clinton Parker, Action!, ANTIC Interview 111, 31 December 2015, hosts: Randy Kindig, Kevin Savetz, Brad Arnold, ANTIC The Atari 8-bit Podcast
  2. ^ Baker, Henry; Parker, Clinton. "Micro SPL". CiteSeerX
  3. ^ Action! Source Code - Page 2, Alfred (Chopper Commander) Posted Mon Feb 2, 2015 1:38 PM, AtariAge Forums, This is the original Action! source as I received it from ICD. It uses the ICD cross assembler which is not included in the zip. It can be easily converted to other formats
  4. ^ a b c d Moriarty, Brian. "Review - Action!". ANALOG Computing (16).
  5. ^ ACTION! in Atariki (PL)
  6. ^ Schneeflock, Ed (March 1985). "Action! A Poor Man's C?". BYTE. p. 273. Retrieved 19 March 2016.
  7. ^ Chadwick, Ian (1985). "Author's Preface To The Revised Edition". Mapping the Atari. Greensboro, North Carolina: Compute! Publications, Inc. pp. v–vi. ISBN 0-87455-004-1.

External links[edit]