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Parentheses and Operator Precedence

As shown in a few examples above, MOO allows you to use parentheses to make it clear how you intend for complex expressions to be grouped. For example, the expression

3 * (4 + 5)

performs the addition of 4 and 5 before multiplying the result by 3.

If you leave out the parentheses, MOO will figure out how to group the expression according to certain rules. The first of these is that some operators have higher precedence than others; operators with higher precedence will more tightly bind to their operands than those with lower precedence. For example, multiplication has higher precedence than addition; thus, if the parentheses had been left out of the expression in the previous paragraph, MOO would have grouped it as follows:

(3 * 4) + 5

The table below gives the relative precedence of all of the MOO operators; operators on higher lines in the table have higher precedence and those on the same line have identical precedence:

!       - (without a left operand)
*       /       %
+       -
==      !=      <       <=      >       >=      in
&&      ||
... ? ... | ... (the conditional expression)

Thus, the horrendous expression

x = a < b && c > d + e * f ? w in y | - q - r

would be grouped as follows:

x = (((a < b) && (c > (d + (e * f)))) ? (w in y) | ((- q) - r))

It is best to keep expressions simpler than this and to use parentheses liberally to make your meaning clear to other humans.

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