Language Specification

Each specification file covers a major area of the language design, and sections are numbered consistently across documents.

1. Leaf

A high-level introduction to Leaf, its compilation pipeline, assumptions, and built-in types.

• 1.1 Pipeline
• 1.2 Assumptions
• 1.3 Built-in Types

2. Language Semantics

Covers the foundational semantic rules of the language: scoping, mutability, visibility, closures, function types, variance, type inference, annotations, constants, literals, operators, and strings.

§2.0–2.3 — Core

• 2.0 Statement Delimiting and Block Syntax
• 2.0.1 Newlines as Statement Terminators
• 2.0.2 Block Bodies
• 2.1 Scoping
• 2.2 Mutability
• 2.3 Visibility

§2.4–2.9 — Functions

• 2.4 Closures and Nested Functions
• 2.5 Function Types
• 2.6 Variance
• 2.6.1 Subtyping in Leaf
• 2.6.2 Function Type Variance
• 2.6.3 Generic Type Variance
• 2.6.4 Variance Checking Rules
• 2.6.5 Summary
• 2.7 Type Inference
• 2.8 Variable Type Annotations
• 2.9 Return Types
• 2.9.1 Implicit Return

§2.10–2.13 — Values and Operations

• 2.10 Constants
• 2.11 Numeric Types and Literals
• 2.11.1 Integer Types
• 2.11.2 Floating-Point Type
• 2.11.3 No Implicit Numeric Conversion
• 2.12 Operators
• 2.12.1 Compound Assignment
• 2.12.2 Operator Precedence and Associativity
• 2.12.3 The ? Propagation Operator
• 2.13 Strings

§2.14–2.17 — Patterns and Syntax

• 2.14 Destructuring, Spread, and Shorthand Syntax
• 2.14.1 Map and Struct Destructuring
• 2.14.2 List Destructuring and Spread
• 2.14.3 Tuple Destructuring
• 2.14.4 Function Parameter Destructuring
• 2.14.5 Shorthand Initialization
• 2.14.6 The _ Discard Binding
• 2.14.7 Spread in Collection Literals
• 2.15 Comments
• 2.16 Variadic Functions
• 2.17 Evaluation Order

3. Type System

Describes the advanced type system features: pattern matching, the never type, generators, for loops, and flow control.

• 3.1 Pattern Matching
• 3.2 The never Type
• 3.3 Generators
• 3.4 For Loops
• 3.5 Flow Control
• 3.5.1 if/else Expressions
• 3.5.2 match Expressions
• 3.5.3 Loops
• 3.5.4 return and Implicit Return

4. Structs, Interfaces, Enums, and Collections

Covers struct declarations, the Self keyword, constructors, generics, interfaces, enums, tuples, collections, and type aliases.

§4.1–4.5 — Core

• 4.1 Structs
• 4.2 The Self Keyword
• 4.3 Constructors
• 4.4 Generics
• 4.5 Interfaces
• 4.5.1 The PartialEq[T] and Eq[T] Interfaces

§4.6–4.9 — Data Types

• 4.6 Enums
• 4.6.1 Simple Enums
• 4.6.2 Enums with Associated Data
• 4.6.3 Generic Enums
• 4.6.4 Built-in Enums
• 4.7 Tuples
• 4.8 Collections
• 4.8.1 Lists
• 4.8.2 Maps
• 4.8.3 Sets
• 4.8.4 Collection Literals
• 4.9 Type Aliases

5. Source Files

Explains .leaf source files and their rules.

• 5.1 .leaf Files — Structured Source

6. Module Resolution

Details how modules are discovered, how imports work (use, @ for external packages, re-exports), path resolution, circular dependency rules, and visibility.

• 6.1 Modules
• 6.2 Project Structure
• 6.3 Import Syntax
• 6.3.1 Project-Local Imports
• 6.3.2 External Package Imports (@)
• 6.3.3 Standard Library Imports (@std)
• 6.3.4 Re-Exports (pub use and pkg use)
• 6.4 Path Resolution Rules
• 6.5 Circular Dependencies
• 6.6 Visibility and Exports

Topic Index

Cross-cutting topics that span multiple spec files: