lists the operators in the Nix expression language, in order of precedence (from strongest to weakest binding). Syntax Associativity Description e . attrpath [ or def ] none Select attribute denoted by the attribute path attrpath from set e. (An attribute path is a dot-separated list of attribute names.) If the attribute doesn’t exist, return def if provided, otherwise abort evaluation. e1 e2 left Call function e1 with argument e2. e ? attrpath none Test whether set e contains the attribute denoted by attrpath; return true or false. e1 ++ e2 right List concatenation. e1 + e2 left String or path concatenation. ! e left Boolean negation. e1 // e2 right Return a set consisting of the attributes in e1 and e2 (with the latter taking precedence over the former in case of equally named attributes). e1 == e2 none Equality. e1 != e2 none Inequality. e1 && e2 left Logical AND. e1 || e2 left Logical OR. e1 -> e2 none Logical implication (equivalent to !e1 || e2).