AppleScript_ The Definitive Guide - Matt Neuburg [140]
But do not imagine that there is some simple rule governing this behavior (such as that AppleScript never coerces the first operand implicitly). In this next example, AppleScript happily coerces both operands implicitly (to a number ):
"3" + "4" -- 7
You see now why the rules for implicit coercion need to be made explicit.
Arithmetic Operators
The arithmetic operators combine numbers to get new numbers in accordance with the usual rules of arithmetic. As in most computer languages, multiplication and division take precedence over addition and subtraction (in the absence of parentheses). So, for example:
3 + 4 * 2 -- 11
3 * 4 + 2 -- 14
An operand that is a list consisting of one number will be coerced to a number. An operand that is a string representing a number, or a list consisting of one such string, will be coerced to a number.
The class of the result of the addition, subtraction, multiplication, and remainder operators is as follows: the result is an integer if the first operand is an integer and if the second operand either is an integer or is a real that can be coerced to an integer without loss of information. Otherwise, the result is a real.
Warning
If you have some programming experience and you know a language such as C or LISP (where if either arithmetic operand is a real, the result is a real), you're going to find AppleScript's behavior surprising. Think of it like this. For the result to be a real, it is not enough that one operand be a real; the first operand must be a real, or else the second operand must have a significant fractional part, not merely a decimal point. Saying x * 1.0, for example, is not a way of making sure you've got a real. When in doubt, coerce explicitly.
Do not blame AppleScript for the phenomena inherent in doing floating-point arithmetic in any language on any computer. It is the nature of computer numerics that most values can only be approximated. Modern processors are extraordinarily clever about compensating, but rounding operations can easily expose the truth:
2.32 * 100.0 div 1 -- 231
Similarly, there may be situations where instead of comparing two values for absolute equality, you will do better to test whether the difference between them lies within some acceptable small epsilon.
Name
+
Synopsis
addition
addition
Syntax
number1 + number2
date +integer
Description
Adds the operands. The addition operator is not overloaded to perform string concatenation; see "Concatenation Operator" (&) later in this chapter. On date arithmetic, see Chapter 13.
Name
-
Synopsis
subtraction ; unary negation
subtraction; unary negation
Syntax
number1 - number2
date - integer
date - date-number
Description
Subtracts the second operand from the first, or negates the single operand. Unary negation has very high precedence . On date arithmetic, see Chapter 13.
Name
*
Synopsis
multiplication
multiplication
Syntax
number * number
Description
Multiplies the operands.
Name
/
Synopsis
real division
real division
Syntax
number1 / number2
Description
Divides the first operand by the second. Both numbers are treated as reals, and the result is a real.
Name
div
Synopsis
integer division
integer division
Syntax
number1 div number2
Description
Obtains the integer part of a division. Both numbers are treated as reals; the first is divided by the second, and the result is coerced to an integer by throwing away its fractional part. Notice that this is not the same as AppleScript's normal real-to-integer coercion behavior. Thus, the way to get the integer part of a real in AppleScript is x div 1, not x as integer.
Example
4 div 5 -- 0
(4 / 5) as integer -- 1
Name
mod
Synopsis
remainder
remainder
Syntax
number1 mod number1
Description
Obtains the remainder from a division. The first operand is divided by the absolute value of the second, and the remainder is returned.