Editing Operator associativity (section)

== Non-associative operators ==
Non-associative operators are operators that have no defined behavior when used in sequence in an expression. In [[Prolog]] the infix operator <code>:-</code> is '''non-associative''' because constructs such as "<code>a :- b :- c</code>" constitute syntax errors.

Another possibility is that sequences of certain operators are interpreted in some other way, which cannot be expressed as associativity. This generally means that syntactically, there is a special rule for sequences of these operations, and semantically the behavior is different. A good example is in [[Python (programming language)|Python]], which has several such constructs.<ref>''[https://docs.python.org/3/reference/ The Python Language Reference],'' "[https://docs.python.org/3/reference/expressions.html 6. Expressions]"</ref> Since assignments are statements, not operations, the assignment operator does not have a value and is not associative. [[Assignment (computer science)#Chained assignment|Chained assignment]] is instead implemented by having a grammar rule for sequences of assignments <code>a = b = c</code>, which are then assigned left-to-right. Further, combinations of assignment and augmented assignment, like <code>a = b += c</code> are not legal in Python, though they are legal in C. Another example are comparison operators, such as <code>&gt;</code>, <code>==</code>, and <code>&lt;=</code>. A chained comparison like <code>a &lt; b &lt; c</code> is interpreted as <code>(a &lt; b) and (b &lt; c)</code>, not equivalent to either <code>(a &lt; b) &lt; c</code> or <code>a &lt; (b &lt; c)</code>.<ref>''[https://docs.python.org/3/reference/ The Python Language Reference],'' "[https://docs.python.org/3/reference/expressions.html 6. Expressions]": [https://docs.python.org/3/reference/expressions.html#comparisons 6.9. Comparisons]</ref>