8.8. Builtin Functions

The syntax for function calls is similar to many other languages.

Like in C++ (namespaces) or Java (packages, classes), functions live in namespaces that are URIs.

Although it is possible to fully write the name of a function, namespace included, it can be cumbersome. Hence, for convenience, a namespace can be associated with a prefix that acts as a shortcut.

JSONiq supports three sorts of functions:

Builtin functions: these have no prefix and can be called without any import.
Local functions: they are defined in the prolog, to be used in the main query. They have the prefix local:. Chapter 12, Prologs describes how to define your own local functions.
Imported functions: they are defined in a library module. They have the prefix corresponding to the alias to which the imported module has been bound to. Chapter 13, Modules describes how to define your own modules.

For now, we only introduce how to call builtin functions -- these are the simplest, since they do not need any prefix or explicit namespace.

Example 8.17. A builtin function call.

keys({ "foo" : "bar", "bar" : "foo" }),
concat("foo", "bar")

Results:

"foo"
"bar"
"foobar"

Some builtin functions perform aggregation and are particularly convenient:

Example 8.18. A builtin function call.

sum(1 to 100),
avg(1 to 100),
count( (1 to 100)[ $$ mod 5 eq 0 ] )

Results:

5050
50.5
20

Remember that JSONiq is a strongly typed language. Functions have signatures, for example sum() expects a sequence of numbers. An error is raised if the actual types do not match the expected types.

Also, calling a function with two parameters is different from calling a function with one parameter that is a sequence with two items. For the latter, extra parentheses must be added to make sure that the sequence is taken as a single parameter.

Example 8.19. Calling a function with a sequence.

count((1, 2, 3, 4))

Results: