nix-super/doc/manual/src/expressions/language-operators.md

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2020-07-23 00:17:48 +03:00
# 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 |
2020-07-23 00:17:48 +03:00
Operators