Lemon_Rust

A port of the Lemon Parser Generator to Rust.

Deprecation Warning!

This project is being deprecated in favor of pomelo, a reimplementation of this very same code as a Rust procedural macro. You should use that for any new code, and also consider porting your existing code.

Introduction

From the original Lemon documentation:

Lemon is an LALR(1) parser generator for C or C++. It does the same job as "bison" and "yacc". But lemon is not another bison or yacc clone. It uses a different grammar syntax which is designed to reduce the number of coding errors. Lemon also uses a more sophisticated parsing engine that is faster than yacc and bison and which is both reentrant and thread-safe.

Change C or C++ to Rust and you will get also the well known benefits of this language.

My thanks and acknowledgement to D. Richard Hipp, the original creator of Lemon.

Differences between Lemon_C and Lemon_Rust

Lemon_Rust works basically the same as Lemon_C. The main difference is, obviously, that it generates Rust code instead of C code. However there are a few other differences, due to the differences in the generated languages.

In the grammar file there are basically the following differences:

1. There is no %name or %token_prefixdirectives. In C all the symbol names are global so this directive allows you to change the name of the generated symbols. In Rust, the generated file will be compiled as a crate and it will have its own namespace. So changing the names of the generated symbols is not needed.
2. There are no destructors (%destructor, %token_destructor and %default_destructor). If you need to write destructors, just implement the Drop trait for the associated type.
3. There is no %token_type directive. In Lemon_C, all tokens must have the same type, while non-terminal symbols may have different types. In Lemon_Rust there is no such distinctions, so you can specify the type for each individual token with %type.
4. There is a new %derive_token directive. It is used to add the #[derive()] directive to the generated Token type.

In the invocation of the program:

1. There is no -m option. That was for writing a makeheaders file, but Rust does not need that.
2. The default template file is not lempar.c but lempar.rs.

Detailed documentation

See the DOCUMENTATION.md file included in the source tree.