LSL Operators
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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; |
| ! ~ ++ -- | Logical-NOT, Bitwise-NOT, Increment, Decrement | counter++; |
| * / % | Multiply/Dot-Product, Divide, Modulus/Cross-Product | 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.
SubNote: As the above bug has been closed as expected behavior, one can only assume the boolean operators have equal precedence.
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.