Action! (programming language)

Action! was one of the earlier examples of the OSS SuperCartridge format. ROM cartridges on the Atari were normally limited to 8 kB, which limited its ability to support larger programs. The SuperCartridge had 16 kB organized as four 4 kB blocks, two of which were visible at any time. The lower 4 kB did not change, and system could bank switch between the other three blocks by changing the value in address $AFFF.[4][5]

Action! used this design by breaking the system into four sections, the editor, the compiler, a monitor for testing code and switching between the editor and compiler, and the run-time library.[5] The run-time library is stored in the cartridge itself. To distribute standalone applications requires a separate run-time package which was sold by OSS as the Action! Toolkit.[6]

Action! constructs were designed to map cleanly to 6502 opcodes, to provide high performance without needing complex optimizations in the one-pass compiler.[7] For example, local variables are assigned fixed addresses in memory, instead of being allocated on the stack of activation records. This eliminates the significant overhead associated with stack management, which is especially difficult in the case of the 6502's 256-byte stack. However, this precludes the use of recursion.[6]

Unlike the integrated Atari BASIC and Atari Assembler Editor environments, the Action! editor 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.[6]

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.[6]

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

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

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

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

 TYPE CORD=[CARD x,y]
 CORD point
 point.x=42
 point.y=23

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       !        @

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

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

BYTE ARRAY FLAGS(8190)

CARD COUNT,I,K,PRIME,TIME

PROC SIEVE()

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

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

  FOR I=0 TO 8190 ; now run the sieve
    DO
    IF FLAGS(I)='T THEN
      PRIME=I+I+3
      K=I+PRIME
      WHILE K<=8190
        DO
        FLAGS(K)='F ; "'F" is a compiler-provided constant for False
        K==+PRIME
        OD
      COUNT==+1
    FI
    OD
  TIME=RTCLOK ; get timer reading
  SDMCTL=34   ; restore screen

  PRINTF("%E %U PRIMES IN",COUNT)
  PRINTF("%E %U JIFFIES",TIME)
RETURN

Brian Moriarty, in a February 1984 review for ANALOG Computing, concluded that Action! was "one of the most valuable development tools ever published for the Atari." He cited the manual as the only weak point of the package, claiming it "suffers from lack of confidence, uncertain organization and a shortage of good, hard technical data."[8]

Leo Laporte reviewed Action in the May/June 1984 edition of Hi-Res. He began the review, "This is the best thing to happen to Atari since Nolan Bushnell figured out people would play ping-pong on a TV screen." Laporte praised the editor, noting its split-screen and cut and paste capabilities and describing it as a "complete word processing system that's very responsive." He said that Action! ran about 200 times as fast as Atari BASIC, concluding that "This language is like a finely tuned racing car."[9]

BYTE in 1985 praised the compilation and execution speed of software written in Action! Using their Byte Sieve benchmark as a test, ten iterations of the sieve completed in 18 seconds in Action!, compared to 10 seconds for assembly and 38 minutes in BASIC. The magazine also lauded the language's editor. BYTE reported that the language resembled C closely enough to "routinely convert programs between the two", and approved of its pointer support. The magazine 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."[10]

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."[11]

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

• Action! (programming language) on SourceForge.net
• Action! Programming Language Version 3.6 - Source Code, by Optimized Systems Software at archive.org
• Action! info at Retrobits.com
• The ACTION! Archive
• Action! language reference
• Effectus cross-compiler