# RustPython/parser
This directory has the code for python lexing, parsing and generating Abstract Syntax Trees (AST).
The steps are:
- Lexical analysis: splits the source code into tokens.
- Parsing and generating the AST: transforms those tokens into an AST. Uses `LALRPOP`, a Rust parser generator framework.
This crate is published on [https://docs.rs/rustpython-parser](https://docs.rs/rustpython-parser).
We wrote [a blog post](https://rustpython.github.io/2020/04/02/thing-explainer-parser.html) with screenshots and an explanation to help you understand the steps by seeing them in action.
For more information on LALRPOP, here is a link to the [LALRPOP book](https://github.com/lalrpop/lalrpop).
There is a readme in the `src` folder with the details of each file.
## Directory content
`build.rs`: The build script.
`Cargo.toml`: The config file.
The `src` directory has:
**lib.rs**
This is the crate's root.
**lexer.rs**
This module takes care of lexing python source text. This means source code is translated into separate tokens.
**parser.rs**
A python parsing module. Use this module to parse python code into an AST. There are three ways to parse python code. You could parse a whole program, a single statement, or a single expression.
**ast.rs**
Implements abstract syntax tree (AST) nodes for the python language. Roughly equivalent to [the python AST](https://docs.python.org/3/library/ast.html).
**python.lalrpop**
Python grammar.
**token.rs**
Different token definitions. Loosely based on token.h from CPython source.
**errors.rs**
Define internal parse error types. The goal is to provide a matching and a safe error API, masking errors from LALR.
**fstring.rs**
Format strings.
**function.rs**
Collection of functions for parsing parameters, arguments.
**location.rs**
Datatypes to support source location information.
**mode.rs**
Execution mode check. Allowed modes are `exec`, `eval` or `single`.
## How to use
For example, one could do this:
```
use rustpython_parser::{parser, ast};
let python_source = "print('Hello world')";
let python_ast = parser::parse_expression(python_source).unwrap();
```