Mojo language reference

Welcome to the Mojo language reference. This documentation provides a concise reference for Mojo's syntax—identifiers, keywords, literals, expressions, operators, statements, function declarations, and more. It's organized by grammar construct and is designed for quick lookup when you need the exact rules, precedence, or form of a specific language element.

Identifiers & keywords

Naming rules, reserved words, escaped identifiers, and argument conventions

Literals

Integer, floating-point, string, t-string, boolean, None, and Self literals

Numeric types

SIMD, DType, Scalar, Int, UInt, integers, floating-point, Byte, literals, and conversions

Operators

Operator precedence, associativity, and implementing operators for custom types

Expressions

Tuples, collection displays, member access, calls, subscripts, ternary conditionals, and comprehensions

Simple statements

Imports, assignments, return, raise, break, continue, and compile-time declarations

Compound statements

If statements, loops, error handling with try/except, context managers, and compile-time control flow

Function declarations

Signatures, parameters, arguments, default values, constraints, effects, and special methods

Struct declarations

Fields, methods, initializers, destructors, and trait conformance for structs

Trait declarations

Required and provided methods, associated types, trait inheritance, trait composition, and conformance

Inline MLIR

Inline MLIR built-ins can call operations that the language doesn't expose natively.

Decorators

Modify or extend the behavior of a struct, function, or other declaration at compile time.