Analyzer

Overview

Hulo's analyzer adopts a layered architecture design, building upon ANTLR4-generated lexical and syntax analyzers, with an additional custom analysis layer to handle complex syntax features.

ANTLR4 Introduction

ANTLR (ANother Tool for Language Recognition) is a powerful parser generator for reading, processing, executing, or translating structured text or binary files. It's widely used to build languages, tools, and frameworks.

Core Features

• Grammar-Driven: Automatically generates parsers from grammar definitions
• Multi-Target Support: Supports multiple target languages including Java, C#, Python, JavaScript, and more
• Powerful Grammar Expression: Supports complex grammar rules and semantic actions
• Rich Toolchain: Provides grammar visualization, debugging, testing, and other tools
• Active Community: Large user community with extensive documentation and resources

How It Works

1. Grammar Definition: Define language rules using ANTLR grammar files (.g4)
2. Code Generation: ANTLR generates lexical and syntax analyzers based on grammar files
3. Parse Tree Construction: Generated parsers convert input text into parse trees
4. Visitor Pattern: Provides Listener and Visitor interfaces for traversing and processing parse trees

Why Choose ANTLR4

Reasons for Choice

• Syntax Complexity: Hulo's syntax is relatively complex, and building a parser from scratch would consume significant effort
• Development Efficiency: Focus on language implementation rather than parser construction, enabling rapid validation of language design
• Maturity and Stability: ANTLR4 is an industry-standard parser generator with rich toolchain support
• Powerful Grammar Expression: Supports complex syntax features such as left recursion, semantic predicates, etc.

Challenges Faced

• Node Control Difficulties: ANTLR-generated AST node operations are less flexible than hand-written parsers
• Customization Limitations: Difficulty in precisely controlling AST structure and node types
• Performance Overhead: Generated code may be less efficient than hand-written parsers
• Learning Curve: Requires mastering ANTLR grammar definition and tool usage

Layered Architecture Design

Layer 1: ANTLR4 Generated Layer

Source Code → Token → ANTLR AST

• Lexer: Converts source code character stream into token stream
• Parser: Converts token stream into ANTLR syntax tree
• Token: Lexical units containing type, value, position, and context information

Layer 2: Hulo Analysis Layer

ANTLR AST → Hulo AST

• Analyzer: Converts ANTLR AST to Hulo's custom AST
• Tracer: Records AST conversion call chains for debugging and optimization

Core Components

Token

Basic unit of lexical analysis, containing:

• Type (keywords, identifiers, literals, etc.)
• Value (specific string or numeric value)
• Position information (line number, column number)
• Context information

Lexer (Lexical Analyzer)

• Identifies keywords, identifiers, literals, operators
• Handles comments, whitespace, line breaks
• Generates token stream for syntax analyzer

Parser (Syntax Analyzer)

• Validates syntax structure correctness
• Builds ANTLR syntax tree
• Handles syntax errors and recovery

Analyzer (Hulo Analyzer)

• Converts ANTLR AST to Hulo AST
• Handles complex semantic analysis
• Type checking and type inference
• Scope analysis

Tracer

• Records complete AST conversion call chains
• Provides detailed debugging information
• Performance analysis and optimization suggestions

Design Advantages

Development Efficiency

• Rapid implementation of complex syntax features
• Focus on language design and semantic analysis
• Reduced parser-related bugs

Maintainability

• Clear separation of responsibilities
• Easy testing and debugging
• Simple extension of new features

Flexibility

• Custom AST structure
• Precise control over node types
• Support for complex semantic analysis

Future Plans

As the project evolves, we may consider:

• Gradually replacing ANTLR with hand-written parsers
• Optimizing AST conversion performance
• Enhancing error handling and recovery mechanisms