Chapter 5. Navigation in JSON content

An implicit iteration is performed on the left-hand-side sequence. $sequence($params) is equivalent to:
```
        for $item in $sequence return $item($params)
```
The semantics of the dynamic function call is then defined on a single item, depending on its type:
- If it is a function, the semantics is the same as defined in XQuery 3.0.
- If it is an object, the dynamic function call is treated as an object lookup if unary, as a key listing if 0-ary. An error jerr:JNTY0018 is raised if there is more than one parameter.
- If it is an array, the dynamic function call is treated as an array lookup if unary, as an array unboxing if 0-ary. An error jerr:JNTY0018 is raised if there is more than one parameter.
- If it is an atomic or an XML node, the dynamic function call if unary or 0-ary always returns the empty sequence. An error jerr:JNTY0018 is raised if there is more than one parameter.

5.1. Object lookup

If the dynamic function call is unary and the left-hand-side is an object, the semantics applied is that of object lookup and is as follows.

The unique parameter is cast to a string $s (an error is raised according to the semantics of casting if this fails).

If $s is in jdm:keys($o) then $o($s) returns the value of the pair with the name $s, i.e. jdm:value($o, $s). Otherwise (i.e., it has no key matching $s), an empty sequence is returned.

Example 5.1. Object lookup

Retrieving a Pair by its name:

Query:

        let $map := { "eyes" : "blue", "hair" : "fuchsia" }
        return $map("eyes")

Result:

        blue

Using Pairs from existing Objects to create a new Object:

Query:

        let $x := { "eyes" : "blue", "hair" : "fuchsia" }
        let $y := { "eyes" : brown, "hair" : "brown" }
        return { "eyes" : $x("eyes"), "hair" : $y("hair") }

Result:

          { "eyes" : "blue", "hair" : "brown" }