9.4 Logical operators

Hollywood supports the following logical operators:

The binary logical operators allow you to make decisions based on multiple conditions. Each binary logical operator needs two operands which are used to evaluate the result of the logical condition. All values that are not 0, Nil or the empty string ("") are considered True.

The And and Or operators use short-cut evaluation. This means that if the first operand already defines the result, the second operand is not evaluated at all. For example, if the first operand of an And expression is False (zero), then the second operand does not need to be evaluated because the whole expression cannot be True anyway. The same applies to an Or expression if the first operand of it is True (non-zero). Then the whole expression will always be True - no matter what value the second operand has.

Please note: And and Or do not return the constant True (1) if they are true. And returns the second operand if it is true and Or returns the first operand if it is true. For example:

a = 5 And 4     ; a = 4
a = 5 And 0     ; a = 0
a = 0 And 4     ; a = 0
b = 5 Or 4      ; b = 5
b = 5 Or 0      ; b = 5
b = 0 Or 4      ; b = 4

The unary Not operator will negate its operand. The result will always be True (1) or False (0). If used on a string it will result in True if the string is empty (""). For example:

a = Not True     ; a = 0 (False)
a = Not False    ; a = 1 (True)
a = Not 5        ; a = 0 (False)
a = Not Not True ; a = 1 (True)
a = Not "Hello"  ; a = 0 (False)
a = Not ""       ; a = 1 (True)

Please note: The Not operator has a high priority. You will need parentheses in most cases. For example, this does not work:

If Not a = -1        ; wrong!

Hollywood will translate it to

If (Not a) = -1

because the Not operator has a higher priority than the equality operator! But obviously this translation does not make any sense because the result of the expression in parentheses (Not a) will always be 0 or 1 but never ever -1. Therefore, if you would like to check if a is not -1, you will have to use parentheses around the expression with the lower priority:

If Not (a = -1)      ; correct!

See Operator priorities for details.

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