Action! (programming language)

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

BYTE is 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

CARDinal is 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

INTeger is 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:

 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

While taking his postgraduate studies, Parker started working part-time at Xerox PARC working on printer drivers. He later moved to the Xerox Alto project where he wrote several games for the system.[6] His PhD was in natural language parsing and he had worked on compiler theory during his graduate work.[7]

Henry Baker and Parker released Micro-SPL in September 1979. Micro-SPL was intended to be used as a systems programming language on the Xerox Alto workstation computer, which was normally programmed in BCPL. The Alto used a microcode system which the BCPL compiler output. Micro-SPL output the same format, allowing BCPL programs to call Micro-SPL programs.[8]

Aside from differences in syntax, the main difference between Micro-SPL and BCPL, and the reason for its existence, was that Micro-SPL produced code that was many times faster than the native BCPL compiler. In general, Micro-SPL programs were expected to run about ten times as fast as BCPL, and about half as fast as good hand-written microcode. In comparison to microcode, they claimed it would take half as long to write and 10% of the time to debug it.[8]

It was during this period that Parker purchased an Atari computer for use at home. He was disappointed with the lack of development systems for it, which was the impetus for creating Action![9] Parker considered releasing the system himself, but decided to partner with Optimized Systems Software (OSS) for sales and distribution. OSS focused on utilities and programming languages like BASIC XL, so this was a natural fit for Action![10] Sales were strong enough for Parker to make a living off the royalties for several years.[11]

The IBM PC had C compilers available, and Parker decided there was no point in porting Action! to that platform.[12] As the sales of the Atari 8-bit computers wound down in North America, OSS wound down as well. Late in its history Action! distribution moved from OSS to Electronic Arts, but they did little with the language and sales ended shortly after.[13] In a 2015 interview, Parker expressed his surprise in the level of interest in the language continued to receive, suggesting it was greater than it had been in the late 1980s.[14]

• Baker, Henry; Parker, Clinton (September 1979). Micro-SPL (PDF) (Technical report). Synapse Computer Services. CiteSeerX 10.1.1.126.6877.
• Parker, Clinton (31 December 2015). "ANTIC Interview 111, Clinton Parker, Action!" (podcast). Interviewed by Randy Kindig.
• Moriarty, Brian (February 1984). "Action! - A new language for the Atari!". ANALOG Computing. No. 16. pp. 54–61.