Editing Action! (programming language) (section)

== Language ==
=== Data types ===
Action! has three fundamental [[data type]]s, all of which are numeric.

'''BYTE''' is internally represented as an [[signedness|unsigned]] 8-[[bit]] integer. Values range from 0 to 255.<br>
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

'''CARD'''inal is internally represented as an [[signedness|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

'''INT'''eger is internally represented as a [[signedness|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

=== Reserved words ===
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.

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

=== Example code ===
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 [[Direct memory access|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