6.4 Parentheses for Grouping
Any expression wrapped in parentheses is also an expression. Like in
C++, but unlike in R, only the round parentheses,
), are allowed. The square brackets
reserved for array indexing and the curly braces
} for grouping statements.
With parentheses it is possible to explicitly group subexpressions
with operators. Without parentheses, the expression
1 + 2 * 3
has a subexpression
2 * 3 and evaluates to 7. With
parentheses, this grouping may be made explicit with the expression
1 + (2 * 3). More importantly, the expression
(1 + 2) * 3 has
1 + 2 as a subexpression and evaluates to 9.