Chapter 13. Modules

You can group functions and variables in separate units, called library modules.

Up to now, everything we encountered were main modules, i.e., a prolog followed by a main query.

A library module does not contain any query - just functions and variables that can be imported by other modules.

A library module must be assigned to a namespace. For convenience, this namespace is bound to an alias in the module declaration. All variables and functions in a library module must be prefixed with this alias.

Example 13.1. A library module.

module namespace my =
    "http://www.example.com/my-module";

declare variable $my:variable := { "foo" : "bar" };
declare variable $my:n := 42;

declare function my:function($i as integer)
{
  $i * $i
};

Once you have defined a library module, you can import it in any other module (library or main). An alias must be given to the module namespace (my). Variables and functions from that module can be accessed by prefixing their names with this alias. The alias may be different than the internal alias defined in the imported module -- only the namespace really matters.

Example 13.2. Importing a library module into a main module.

import module namespace other =
    "http://www.example.com/my-module";
other:function($other:n)

Results:

An engine may come with a number of builtin library modules. For example, there is the standardized math module.

Example 13.3. Using the math module.

import module namespace math =
    "http://www.w3.org/2005/xpath-functions/math";
math:pi(),
math:pow(2, 30),
math:exp(1),
math:exp10(2),
math:log(1),
math:log10(2),
math:sqrt(4),
math:sin(math:pi())

Results:

3.1415926535897931
1.073741824E9
2.7182818284590451
100
0
0.3010299956639812
2
1.2246467991473532E-16