Expression Language

Expr is the expression and scripting language used by PlanetCNC for calculations, automation logic, machine customization, and integration tasks.

Use these pages depending on what you need:

• New to Expression? Start with the Tutorials.
• Already know the basics? Use the How-To Guides for task-oriented help.
• Need exact syntax or behavior? Use the Reference Manual.
• Want examples to adapt? Use the Cookbook.

Start here if you are learning Expression for the first time:

1. What is Expr?
2. First expression
3. Values, variables, and assignment
4. Operators and conditions
5. Control flow
6. Functions and methods
7. Scope and set
8. Classes and objects
9. none(), nan(), and errors
10. Complete examples

Use these pages when you already understand programming basics and want to learn Expression quickly:

1. Lexical basics
2. Type system
3. Variables and assignment
4. Operators
5. Control flow
6. Functions
7. Built-in functions

The tutorials teach Expression step by step. They are intended to be read in order.

Open tutorials

How-to guides explain how to solve common tasks, such as writing conditions, using loops, organizing code, handling missing values, and debugging errors.

Open how-to guides

The reference manual defines the language syntax, values, operators, control flow, functions, classes, error behavior, execution model, and limits.

Open reference manual

The cookbook contains practical examples that can be copied, modified, and reused.

Open cookbook

Expression language documentation is being migrated from the old draft page and from the internal reference chapters. Some pages may still be incomplete while this work is in progress.