Every XLOG file is a module. Larger programs are assembled by importing modules into one another, so you can keep predicates, functions, and type aliases where they belong and pull in only what a given file needs.

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Importing

Bring another module into scope with use, giving its path. The / character is the path separator between path segments: 
use utils/math.
To import only specific names, list them in braces after ::: 
use utils/math::{abs_diff, clamp}.
The selective form imports exactly the named predicates or functions and nothing else, which keeps a module’s dependencies explicit.

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Visibility

Predicates and functions are public by default — once a module is imported, its declarations are visible to the importer. Mark a declaration private to hide it, so it stays internal to its own module and never leaks across a use: 
private pred scratch(u32).

private func normalize(X: f64) -> f64 = X / total().
Both pred and func accept the private modifier. Use it for helpers that support a module’s public surface but are not meant to be part of it.

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Domain aliases

A domain declaration names a reusable type. Write domain name : type. to introduce an alias you can then use anywhere a type is expected: 
domain node : u32.

pred edge(src: node, dst: node).
Here node stands for u32, so the intent of each column is visible at a glance and a later change to the underlying type is made in one place.

Pragmas

Set compiler and engine behavior from inside a program with #pragma directives.