YAAL Parser Implementation

This project contains both Python (Lark) and C++ (PEGTL) implementations of parsers for the YAAL (Yet Another Abstract Language) specification.

YAAL Language Features

YAAL is a flexible, statement-based language that supports:

• Dual nature: Same syntax for data structures and executable programs
• Statement model: Simple statements (no colons) and compound statements (key:value)
• First colon rule: Everything before first colon = key, everything after = value
• Shebang support: Context switching with #!pipeline, #!hibrid-code, etc.
• Brace blocks: Raw content containers with balanced brace matching
• Triple-quoted strings: Multiline string support
• Flexible keys: Keys can contain spaces and special characters
• Indentation-based nesting: Spaces-only (no tabs)

Parser Implementations

C++ Parser (PEGTL)

Location: src/cpp/

Features:

• Complete YAAL specification compliance
• Fast parsing with PEGTL library
• Detailed AST visitor pattern
• Comprehensive error handling

Building:

cmake -B build -S src/cpp
cmake --build build

Usage:

./build/yaal <filename.yaal>

Python Parser (Lark)

Location: src/py/yaal/

Features:

• YAAL grammar in Lark format
• Python indentation handling
• Command-line interface
• Graceful dependency handling

Dependencies:

pip install lark

Usage:

python3 src/py/yaal/yaal.py <filename.yaal>

Example YAAL Files

Basic Example (test_input.yaal)

#!pipeline
name: John
api endpoint: https://api.example.com:8080/v1
production
config:
  debug: false
  timeout: 30
script: { echo hello; exit 0 }

Comprehensive Example (comprehensive_test.yaal)

Demonstrates all YAAL features including:

• Shebang lines
• Simple and compound statements
• Keys with spaces
• Triple-quoted strings
• Brace blocks
• Nested structures
• Polymorphic lists

Grammar Highlights

Lark Grammar (src/py/yaal/yaal.lark)

start: [shebang_line] file_input

shebang_line: \"#!\" IDENTIFIER _NEWLINE

?stmt: simple_stmt | compound_stmt

simple_stmt: line_content _NEWLINE
compound_stmt: key_part \":\" value_part _NEWLINE?

brace_block: \"{\" brace_content \"}\"
quoted_string: ESCAPED_STRING | TRIPLE_QUOTED_STRING

PEGTL Grammar (src/cpp/yaal.cpp)

struct shebang_line : pegtl::seq<pegtl::string<'#', '!'>, identifier, pegtl::eol> {};
struct simple_stmt : pegtl::seq<line_content, _NEWLINE> {};
struct compound_stmt : pegtl::seq<key_part, pegtl::one<':'>, /* ... */> {};
struct brace_block : pegtl::seq<pegtl::one<'{'>, brace_content, pegtl::one<'}'>> {};

Testing

Both parsers have been tested with:

• Basic YAAL syntax
• Complex nested structures
• All string types (unquoted, quoted, triple-quoted)
• Brace blocks with nested content
• Real-world examples from the YAAL specification

Compliance

✅ Complete YAAL specification compliance
✅ All examples from https://github.com/zokrezyl/yaal-lang parse successfully
✅ Proper error handling and reporting
✅ Extensible architecture for semantic analysis

Next Steps

1. Semantic Analysis: Add interpretation and execution capabilities
2. Context Handlers: Implement shebang-based context switching
3. Integration: Connect to YAAL execution engines
4. Tooling: Add syntax highlighting, LSP support, etc.

Both parsers provide a solid foundation for building YAAL-based tools and applications.