Download Learning ZIL

Page 69
Learning ZIL
2/25/2002
Appendix D: ZIL Instructions
ZIL instructions, also called op-codes, are the method by which you
communicate with the interpreter. This is just a partial list; some op-codes are so
obscure you'll never need to know them. A complete description of every
instruction can be found in the ZIP Specification.
In the list below, arguments to the instruction are listed after the name of the
instruction. Optional arguments are italicized.
Arithmetic Instructions
ADD integer1 integer2
Adds the two given numbers and returns the sum. This usually appears in ZIL
code as a "+"—the compiler changes it to "ADD." Example:
<+ ,FRONT-SEAT-PASSENGERS ,BACK-SEAT-PASSENGERS>
SUB integer1 integer2
Subtracts integer2 from integer1 and returns the difference. The compiler
changes "-" to "SUB." Example:
<- ,LT-BLATHER-ANGER 5>
MUL integer1 integer2
Multiplies the two given numbers and returns the product. The compiler changes
"*" to "MUL." Example:
<* <MARTIANS-IN-ROOM> ,ANTENNA-ON-A-MARTIAN>
DIV integer1 integer2
Divides integer1 by integer2 and returns the quotient, truncated to an integer if
necessary. The compiler changes "/" to "DIV." Example:
</ ,SCREEN-WIDTH 2>
MOD integer1 integer2
Divides integer1 by integer2 and returns the remainder. Example:
<MOD ,PEBBLES-IN-PILE 10>
RANDOM integer
Returns a random number between one and the given number, inclusive.
Example:
<RANDOM 17>
Predicate Instructions
EQUAL? arg1 arg2 arg3 arg4
Returns true if arg1 is equal? to any of the subsequent args. Example:
<EQUAL? ,HERE ,OVAL-OFFICE ,ROSE-GARDEN ,PORTICO>
ZERO? arg
Returns true if the value of arg is zero. This often appears as
<EQUAL? ,WHATEVER 0>
in your game code; the compiler converts it to the ZERO? instruction. Example:
<ZERO? ,FUEL-LEVEL>
LESS? integer1 integer2
Returns true if integer1 is less than integer2. The compiler converts L? to
LESS?. Example:
<L? ,AIR-PRESSURE 4>