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.
Associativity: none
Precedence: 1
## Application
> *e1* *e2*
Call function *e1* with argument *e2*.
Associativity: left
Precedence: 2
## Arithmetic Negation
> `-` *e*
Arithmetic negation.
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*
List concatenation.
Associativity: right
Precedence: 5
## Multiplication
> *e1* `*` *e2*,
Arithmetic multiplication.
Associativity: left
Precedence: 6
## Division
> *e1* `/` *e2*
Arithmetic division.
Associativity: left
Precedence: 6
## Addition
> *e1* `+` *e2*
Arithmetic addition.
Associativity: left
Precedence: 7
## Subtraction
> *e1* `-` *e2*
Arithmetic subtraction.
Associativity: left
Precedence: 7
## String Concatenation
> *string1* `+` *string2*
String concatenation.
Associativity: left
Precedence: 7
## Not
> `!` *e*
Boolean negation.
Associativity: none
Precedence: 8
## Update
> *e1* `//` *e2*
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).
Associativity: right
Precedence: 9
## Less Than
> *e1* `<` *e2*,
Arithmetic/lexicographic comparison.
Associativity: none
Precedence: 10
## Less Than or Equal To
> *e1* `<=` *e2*
Arithmetic/lexicographic comparison.
Associativity: none
Precedence: 10
## Greater Than
> *e1* `>` *e2*
Arithmetic/lexicographic comparison.
Associativity: none
Precedence: 10
## Greater Than or Equal To
> *e1* `>=` *e2*
Arithmetic/lexicographic comparison.
Associativity: none
Precedence: 10
## Equality
> *e1* `==` *e2*
Equality.
Associativity: none
Precedence: 11
## Inequality
> *e1* `!=` *e2*
Inequality.
Associativity: none
Precedence: 11
## Logical AND
> *e1* `&&` *e2*
Logical AND.
Associativity: left
Precedence: 12
## Logical OR
> *e1* <code>||</code> *e2*
Logical OR.
Associativity: left
Precedence: 13
## Logical Implication
> *e1* `->` *e2*
Logical implication (equivalent to <code>!e1 || e2</code>).
