Difference between revisions of "LSL Operators"
(added examples for ++ and  use) 

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will cause a Math Error rather than say "Aha".  will cause a Math Error rather than say "Aha".  
+  
+  '''Note:''' The ++ (increment) and  (decrement) have their effect on their number either before or after the number is evaluated when used in conditions dependent on whether they are before or after the number.  
+  
+  <lsl>integer count;  
+  if(!(++count)) // Is incremented then evaluated.  
+  llSay(0, "Aha"); // Will not be said.</lsl>  
+  
+  <lsl>integer count;  
+  if(!(count++)) // Is evaluated then incremented.  
+  llSay(0, "Aha"); // Will be said.</lsl>  
Revision as of 21:40, 7 October 2009
LSL Portal  Functions  Events  Types  Operators  Constants  Flow Control  Script Library  Categorized Library  Tutorials 
Operators are used to cause an operation (or mathematical action) to be performed on one (such as !) or two operands. The easy and common example is 1 + 2 where 1 and 2 are operands, and the + is the operator.
This concept can be extended much further with LSL since operands can be variables with the special case of the assignment operators requiring that the left hand side be a variable.
Operator  Description  Usage Example 

()  Parentheses  a * (b + c) 
[]  Brackets: list constructor  [a, 2, "this", 0.01] 
(type)  Typecasting  message = "The result is:" + (string) result; 
! ~ ++   BinaryNOT, BitwiseNOT, Increment, Decrement  counter++; 
* / %  Multiply/DotProduct, Divide, Modulus/CrossProduct  rollover = (count + 1)%5; 
  Subtraction  one = 3  2; 
+  Addition or joining Strings  two = 1+1;
text = "Hello" + "World"; 
+  Concatenation or joining Lists  myList = [1, 2, 3] + [4, 5];
newList = oldList + addList; 
<< >>  Left Shift, Right Shift  eight = 4 << 1; 
< <= > >=  Less Than, Less Than Or Equal To,
Greater Than, Greater Than or Equal To 
isFalse = (6 <= 4); 
== !=  Comparison Equal, Comparison Not Equal  isFalse = ("this" == "that"); 
&  Bitwise AND  zero = 4 & 2;
four = 4 & 4; 
^  Bitwise XOR  zero = 4 ^ 4;
six = 4 ^ 2; 
  Bitwise OR  four = 4  4;
six = 4  2; 
  Logical OR  isTrue = (FALSE  TRUE); 
&&  Logical AND  isFalse = (FALSE && TRUE); 
= += = *= /= %=  Assignment  four = 4; 
Note: Unlike most, if not all, other languages that use the C style && and  operators, both operands are always evaluated. For example,
<lsl>if (TRUE  1/0) llSay( 0, "Aha!" );</lsl>
will cause a Math Error rather than say "Aha".
Note: The ++ (increment) and  (decrement) have their effect on their number either before or after the number is evaluated when used in conditions dependent on whether they are before or after the number.
<lsl>integer count; if(!(++count)) // Is incremented then evaluated. llSay(0, "Aha"); // Will not be said.</lsl>
<lsl>integer count; if(!(count++)) // Is evaluated then incremented. llSay(0, "Aha"); // Will be said.</lsl>
Note: The order of precedence of boolean operators is unclear. It is possible that there is a bug in the expression parser, making precedence inconsistent, or it may simply be that  and && have equal precedence; testing is inconclusive. Thus, when in doubt, parenthesize.
Note: The order of evaluation appears to be backwards from most languages. If the value of x starts as 1 then the first two conditions below evaluate false and the second two evaluate true:
<lsl>(x && (x = 0) == 0 && x)</lsl> <lsl>(x && (x = 0) == 0 && x == 0)</lsl> <lsl>(x == 0 && (x = 0) == 0)</lsl> <lsl>(x == 0 && (x = 0) == 0 && x)</lsl>
Both sides are evaluated regardless of the the truth of either side.
Left Type  Right Type  Result Type  Description 

integer  integer  integer  Adds left and right 
integer  float  float  Adds left and right 
float  integer  float  Adds left and right 
string  string  string  Concatenates right onto the end of left. 
list  *  list  Concatenates right onto the end of left. 
*  list  list  Affixes left onto the start of right. 
vector  vector  vector  Adds left and right 
rotation  rotation  rotation  Adds left and right Not useful for combining rotations, use * or / instead. 
Simple assignment operator  Shorthand operator 

a = a + 1  a += 1 
a = a – 1  a = 1 
a = a * (n+1)  a *= (n+1) 
a = a / (n+1)  a /= (n+1) 
a = a % b  a %= b 
De Morgan's laws
AND  OR 

~(a & b) 
~a  ~b

~a & ~b 
~(a  b)

a & ~b 
~(~a  b)

~(a & ~b) 
~a  b

AND  OR 

!(a && b) 
!a  !b

!a && !b 
!(a  b)

a && !b 
!(!a  b)

!(a && !b) 
!a  b

Due to De Morgan's laws, by row code in the AND column is logically equivalent to code in the OR. a and b need not be variables, they can be expressions. In certain circumstances these equivalencies can be used to simplify complex code. It is important not to confuse the two sets when using them. The first two rows depict De Morgan's laws as it is formulated, the second two build upon it.