lix/doc/manual/src/expressions/language-operators.md

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2020-07-22 21:17:48 +00:00
# Operators
[table\_title](#table-operators) lists the operators in the Nix
expression language, in order of precedence (from strongest to weakest
binding).
| Name | Syntax | Associativity | Description | Precedence |
| ------------------------ | ----------------------------- | ------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ---------- |
| Select | 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 doesnt exist, return def if provided, otherwise abort evaluation. | 1 |
| Application | e1 e2 | left | Call function e1 with argument e2. | 2 |
| Arithmetic Negation | `-` e | none | Arithmetic negation. | 3 |
| Has Attribute | e `?` attrpath | none | Test whether set e contains the attribute denoted by attrpath; return `true` or `false`. | 4 |
| List Concatenation | e1 `++` e2 | right | List concatenation. | 5 |
| Multiplication | e1 `*` e2, | left | Arithmetic multiplication. | 6 |
| Division | e1 `/` e2 | left | Arithmetic division. | 6 |
| Addition | e1 `+` e2 | left | Arithmetic addition. | 7 |
| Subtraction | e1 `-` e2 | left | Arithmetic subtraction. | 7 |
| String Concatenation | string1 `+` string2 | left | String concatenation. | 7 |
| Not | `!` e | none | Boolean negation. | 8 |
| Update | 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). | 9 |
| Less Than | e1 `<` e2, | none | Arithmetic comparison. | 10 |
| Less Than or Equal To | e1 `<=` e2 | none | Arithmetic comparison. | 10 |
| Greater Than | e1 `>` e2 | none | Arithmetic comparison. | 10 |
| Greater Than or Equal To | e1 `>=` e2 | none | Arithmetic comparison. | 10 |
| Equality | e1 `==` e2 | none | Equality. | 11 |
| Inequality | e1 `!=` e2 | none | Inequality. | 11 |
| Logical AND | e1 `&&` e2 | left | Logical AND. | 12 |
| Logical OR | e1 `\|\|` e2 | left | Logical OR. | 13 |
| Logical Implication | e1 `->` e2 | none | Logical implication (equivalent to `!e1 \|\|
e2`). | 14 |
Operators