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# Operators
## Attribute selection
> *e* `.` *attrpath* \[ `or` *def* \]
Select the attribute denoted by attribute path *attrpath* from attribute 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.
Associativity: none
Precedence: 1
## Function application
> *f* *e*
Call function *f* with argument *e*.
Associativity: left
Precedence: 2
## Arithmetic negation
> `-` *e*
Associativity: none
Precedence: 3
## Has attribute
> *e* `?` *attrpath*
Test whether set *e* contains the attribute denoted by *attrpath*; return `true` or `false`.
Associativity: none
Precedence: 4
## List concatenation
> *e1* `++` *e2*
Concatenate lists *e1* and *e2*.
Associativity: right
Precedence: 5
## Multiplication
> *e1* `*` *e2*,
Multiply numbers *e1* and *e2*.
Associativity: left
Precedence: 6
## Division
> *e1* `/` *e2*
Divide numbers *e1* and *e2*.
Associativity: left
Precedence: 6
## Addition
> *e1* `+` *e2*
Add numbers *e1* and *e2*.
Associativity: left
Precedence: 7
## Subtraction
> *e1* `-` *e2*
Subtract numbers *e2* from *e1*.
Associativity: left
Precedence: 7
## String concatenation
> *string1* `+` *string2*
Concatenate *string1* and *string1* and merge their string contexts.
Associativity: left
Precedence: 7
## Logical negation (`NOT`)
> `!` *e*
Negate the Boolean value *e*.
Associativity: none
Precedence: 8
## Merge attribute sets
> *e1* `//` *e2*
Return a set consisting of all the attributes in *e1* and *e2*.
If an attribute name is present in both, the attribute value from the former is taken.
Associativity: right
Precedence: 9
## Less than
> *e1* `<` *e2*,
- Arithmetic comparison for numbers
- Lexicographic comparison for strings and paths
- Lexicographic comparison for lists:
Elements at the same index in both lists are compared according to their type and skipped if they are equal.
Associativity: none
Precedence: 10
## Less than or equal to
> *e1* `<=` *e2*
- Arithmetic comparison for numbers
- Lexicographic comparison for strings and paths
- Lexicographic comparison for lists:
Elements at the same index in both lists are compared according to their type and skipped if they are equal.
Associativity: none
Precedence: 10
## Greater than
> *e1* `>` *e2*
- Arithmetic comparison for numbers
- Lexicographic comparison for strings and paths
- Lexicographic comparison for lists:
Elements at the same index in both lists are compared according to their type and skipped if they are equal.
Associativity: none
Precedence: 10
## Greater than or equal to
> *e1* `>=` *e2*
- Arithmetic comparison for numbers
- Lexicographic comparison for strings and paths
- Lexicographic comparison for lists:
Elements at the same index in both lists are compared according to their type and skipped if they are equal.
Associativity: none
Precedence: 10
## Equality
> *e1* `==` *e2*
Check *e1* and *e2* for equality.
- Attribute sets and lists are compared recursively, and therefore are fully evaluated.
- Comparison of functions always returns `false`.
- Integers are coerced to floating point numbers if compared to floating point numbers.
- Floating point numbers only differ up to a limited precision.
Associativity: none
Precedence: 11
## Inequality
> *e1* `!=` *e2*
Equivalent to `! (`*e1* `==` *e2* `)`
Associativity: none
Precedence: 11
## Logical conjunction (`AND`)
> *e1* `&&` *e2*
Return `true` if and only if both `e1` and `e2` evaluate to `true`, otherwise `false`.
Associativity: left
Precedence: 12
## Logical disjunction (`OR`)
> *e1* `||` *e2*
Return `true` if at least `e1` or `e2` evaluate to `true`, otherwise `false`.
Associativity: left
Precedence: 13
## Logical implication
> *e1* `->` *e2*
Return `false` if *e1* evaluates to `true` and *e2* evaluates to `false`, otherwise `true`.
Equivalent to `!`*e1* `||` *e2*.
Associativity: none
Precedence: 14
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