Features
Main Features
- Earley parser, capable of parsing any context-free grammar
- Implements SPPF, for efficient parsing and storing of ambiguous grammars.
- LALR(1) parser, limited in power of expression, but very efficient in space and performance (O(n)).
- Implements a parse-aware lexer that provides a better power of expression than traditional LALR implementations (such as ply).
- EBNF-inspired grammar, with extra features (See: Grammar Reference)
- Builds a parse-tree (AST) automagically based on the grammar
- Stand-alone parser generator - create a small independent parser to embed in your project.
- Flexible error handling by using a "puppet parser" mechanism (LALR only)
- Automatic line & column tracking (for both tokens and matched rules)
- Automatic terminal collision resolution
- Standard library of terminals (strings, numbers, names, etc.)
- Unicode fully supported
- Extensive test suite
- MyPy support using type stubs
- Python 2 & Python 3 compatible
- Pure-Python implementation
Extra features
- Import rules and tokens from other Lark grammars, for code reuse and modularity.
- Support for external regex module (see here)
- Import grammars from Nearley.js (read more)
- CYK parser
- Visualize your parse trees as dot or png files (see_example)
Experimental features
- Automatic reconstruction of input from parse-tree (see examples)
Planned features (not implemented yet)
- Generate code in other languages than Python
- Grammar composition
- LALR(k) parser
- Full regexp-collision support using NFAs