Uses old Rust 2015
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RustLex: lexical analysers generator for Rust
RustLex is a lexical analysers generator, i.e. a program that generate lexical analysers for use in compiler from a description of the language using regular expressions. It is similar to the well-known Lex but is written in Rust and outputs Rust code as the analyser. It differs from Lex by using Rust's new syntax extensions system as the interface for defining lexical analysers. The description of the analyser thus can be directly embedded into a Rust source file, and the generator code will be called by Rustc at the macro-expansion phase.
Rustlex availibility and rust compatibility
Rustlex using syntax extensions, it has to deal with rustc libsyntax
.
libsyntax
is more or less the compiler guts, and it has been explicitely
excluded from the Rust 1.0 roadmap. Bottom line is, RustLex inline syntax
generation will not be usable with Rust 1.0.
The way of using RustLex depends on the version of Rust you are using to build your project.
Nightly
This is the easy way. Just indicate a dependency to rustlex
in your Cargo.toml
and add the following lines at the top of your crate:
#![feature(plugin)]
#![plugin(rustlex)]
#[allow(plugin_as_library)] extern crate rustlex;
#[macro_use] extern crate log;
This will make rustc
load the RustLex plugin which contains everything that
is needed to generate the code.
Stable
On the stable channel, you have to use [syntex]
(https://github.com/erickt/rust-syntex) to first perform code generation and then
include!()
the produced code into your project.
Your Cargo.toml
should look like that:
[package]
name = "your package"
version = "0.0.0"
build = "build.rs"
[build-dependencies]
rustlex_codegen = { version = "*", features = ["with-syntex"] }
syntex = { version = "*", optional = true }
[dependencies]
rustlex_codegen = { version = "*", features = ["with-syntex"] }
You will need to write a build.rs
file. This file is automatically called by
cargo
before the build (according to the build
variable in the Cargo.toml
file). In our case, it will use syntex to process your code and call RustLex's
code generation:
pub fn main() {
extern crate syntex;
extern crate rustlex_codegen;
use std::env;
use std::path::Path;
let mut registry = syntex::Registry::new();
rustlex_codegen::plugin_registrar(&mut registry);
let src = Path::new("src/foo.in.rs");
let dst = Path::new(&env::var_os("OUT_DIR").unwrap()).join("foo.rs");
registry.expand("", &src, &dst).unwrap();
}
Replace foo.in.rs
by the name of the file in which you will use RustLex. Note
that all its submodules are processed with it, so you don't need to add them as
well even if they also contain calls to the RustLex macro.
This will generate a file called foo.rs
(or however you named it) in Cargo's
OUT_DIR
. To use this file, add something like this somewhere in your project
(for example in a foo.rs
file placed alongside foo.in.rs
):
If you want to build a project using RustLex that can be built using either
stable or nightly, you can write a portable Cargo.toml
file using features,
and use the #[cfg()]
attribute in your build.rs
and the rest of your code to
make it build using both versions. You can check out the [test project]
(http://github.com/LeoTestard/RustLex/tree/master/codegen/tests/Cargo.toml/) for
rustlex_codegen
for an example.
Defining a lexer
You can then invoke the rustlex!
macro anywhere. The macro will expand into a
single lexer structure and implementation describing the lexical analyser.
The rustlex!
macro takes as argument the name of the structure and the
description of the lexical analyser. The description consists of two parts:
- definitions of regular expressions
- definitions of rules
A minimum lexer will look like:
rustlex! SimpleLexer {
// expression definitions
let A = 'a';
// then rules
A => |lexer:&mut SimpleLexer<R>| Some(TokA ( lexer.yystr() ))
}
More complex regular expression definition examples can be found in a more complex example. It is worth noting that:
- characters (standalone or in character class) and strings have to be quoted as in rust or C (simple quote for character, double quote for strings)
- an expression definition can be "called" by its identifier in another expression
Using a lexer
The lexer will read characters from a standard rust Reader
and implement a
Token
iterator
.
let inp = BufReader::new("aa".as_bytes());
let mut lexer = SimpleLexer::new(inp);
for tok in lexer {
...
}
Advanced lexer features
Token enumeration
By default, rustlex!
assumes the existence of a token enumeration named
Token
in the same module, but this name can be overriden when needed as is the
case for the OtherLexer
from this example.
Conditions
As in flex, conditions can be defined to have the lexer switch from one mode to another.
Check out this example.
Arbitrary lexer properties and methods
It is possible to add specific fields to the lexer structure using the
property
keyword as shown there.
Lexer methods (to be called from action code) can also be defined by a normal
impl
section.