Common operator notation: Difference between revisions

Revision as of 21:35, 7 September 2013

Revision as of 13:25, 28 January 2014

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In terms of operator position, an operator may be prefix, postfix, or infix. A prefix operator immediately precedes its operand, as in −x. A postfix operator immediately succeeds its operand, as in x! for instance. An infix operator is positioned in between a left and a right operand, as in x+y. Some languages, most notably the C-syntax family, stretches this conventional terminology and speaks also of ''ternary'' infix operators (a?b:c). Theoretically it would even be possible (but not necessarily practical) to define parenthesization as an n-ary bifix operation.

'''[[Operator associativity]]''', determines what happens when an operand is surrounded by operators of the same precedence, as in 1-2-3: An operator can be left-associative, right-associative, or non-associative. Left-associative operators are applied to operands in left-to-right order while right-associative operators are the other way round. The basic arithmetic operators are normally all left-associative, which means that 1-2-3 = (1-2)-3 ≠ 1-(2-3), for instance. In programming languages where assignment is implemented as an operator, that operatioroperator is often right-associative. If so, a statement like a := b := c would be equivalent to a := (b := c), which means that the value of c is copied to b which is then copied to a. An operator which is non-associative cannot compete for operands with operators of equal precedence. In [[Prolog]] for example, the infix operator :- is non-associative, so constructs such as a :- b :- c are syntax errors.

Unary prefix operators such as − (negation) or sin (trigonometric function) are typically associative prefix operators. When more than one associative prefix or postfix operator of equal precedence precedes or succeeds an operand, the operators closest to the operand goes first. So −sin x = −(sin x), and sin -x = sin(-x).