rust-hl-lua

This library is a high-level binding for Lua 5.2. You don't have access to the Lua stack, all you can do is read/write variables (including callbacks) and execute Lua code.

How to install it?

Add this to the Cargo.toml file of your project

[dependencies.rust-hl-lua]
git = "https://github.com/tomaka/rust-hl-lua"

In the future, this library will directly include the Lua C library if cargo allows this.

How to use it?

extern crate lua = "rust-hl-lua";
use lua::Lua;

The Lua struct is the main element of this library. It represents a context in which you can execute Lua code.

let mut lua = Lua::new();     // mutable is mandatory

You can check the documentation here.

Reading and writing variables

lua.set("x", 2);
lua.execute("x = x + 1").unwrap();
let x: int = lua.get("x").unwrap();  // x is equal to 3

Reading and writing global variables of the Lua context can be done with set and get. The get function returns an Option<T> and does a copy of the value.

The base types that can be read and written are: int, i8, i16, i32, uint, u8, u16, u32, f32, f64, bool, String.

If you wish so, you can also add other types by implementing the Pushable and CopyReadable/ConsumeReadable traits.

Executing Lua

let x: uint = lua.execute("return 6 * 2;").unwrap();    // equals 12

The execute function takes a &str and returns a Result<Readable, ExecutionError>.

You can also call execute_from_reader which takes a std::io::Reader as parameter. For example you can easily execute the content of a file like this:

lua.execute_from_reader(File::open(&Path::new("script.lua")).unwrap())

Writing functions

fn add(a: int, b: int) -> int {
    a + b
}

lua.set("add", add);
lua.execute("local c = add(2, 4)");
lua.get("c").unwrap();  // return 6

In Lua, functions are exactly like regular variables.

You can write regular functions as well as closures:

lua.set("mul", |a:int,b:int| a*b);

Note that the lifetime of the Lua context must be equal to or shorter than the lifetime of closures. This is enforced at compile-time.

let mut a = 5i;

{
    let mut lua = Lua::new();

    lua.set("inc", || a += 1);
    for i in range(0i, 15) {
        lua.execute::<()>("inc()").unwrap();
    }
} // unborrows `a`

assert_eq!(a, 20)

Error handling

If your Rust function returns a Result object which contains an error, then a Lua error will be triggered.

Manipulating Lua tables

Manipulating a Lua table can be done by reading a LuaTable object.

let mut table: rust-hl-lua::LuaTable = lua.load("a").unwrap();

Note that we use the load function instead of get function, because reading a LuaTable mutably borrows the Lua context.

You can then iterate through the table with the .iter() function. Note that the value returned by the iterator is an Option<(Key, Value)>, the Option being empty when either the key or the value is not convertible to the requested type. The filter_map function (provided by the standard Iterator trait) is very useful when dealing with this.

for (key, value) in table.iter().filter_map(|e| e) {
    ...
}

You can also retreive and modify individual indices:

let x = table.get("a").unwrap();
table.set("b", "hello");

Calling Lua functions

You can call Lua functions by reading a functions_read::LuaFunction.

lua.execute("
    function get_five() 
        return 5
    end");

let get_five: functions_read::LuaFunction = lua.load("get_five").unwrap();
let value: int = get_five().unwrap();
assert_eq!(value, 5);

This object holds a mutable reference of Lua, so you can't read or modify anything in the Lua context while the get_five variable exists. It is not possible to store the function for the moment, but it may be in the future.

Reading and writing Rust containers

(note: not yet possible to read containers)

It is possible to read and write whole Rust containers at once:

lua.set("a", [ 12, 13, 14, 15 ]);

If the container has single elements, then the indices will be numerical. For example in the code above, the 12 will be at index 1, the 13 at index 2, etc.

If the container has tuples of two elements, then the first one will be considered as the key and the second one as the value.

This can be useful to create APIs:

fn foo() { }
fn bar() { }

lua.set("mylib", [
    ("foo", foo),
    ("bar", bar)
]);

lua.execute("mylib.foo()");

Creating a Lua module

This library also includes a second library named rust-hl-lua-module which allows you to create Lua modules in Rust.

To use it, add this to Cargo.toml:

[dependencies.rust-hl-lua-modules]
git = "https://github.com/tomaka/rust-hl-lua"

Then you can use it like this:

#![feature(phase)]

#[phase(plugin)]
extern crate lua_mod = "rust-hl-lua-modules";

#[export_lua_module]
pub mod mylib {         // <-- must be the name of the Lua module
    static PI: f32 = 3.141592;

    fn function1(a: int, b: int) -> int {
        a + b
    }

    fn function2(a: int) -> int {
        a + 5
    }

    #[lua_module_init]
    fn init() {
        println!("module initialized!")
    }
}

This module will then be usable by Lua:

> mylib = require("mylib")
> return mylib.function1(2, 4)
6
> return mylib.PI
3.141592

Roadmap

• Reading/writing inside Lua tables
  • Iterating through tables
  • Reading elements by value
  • Reading functions and sub-tables
• Reading/writing containers
  • Vectors and slices
  • HashMaps and HashSets
• Writing functions
  • Basic support
  • Functions with parameters
  • Closures
• Reading or loading a function and calling it later
  • Basic support
  • Passing parameters
• Access to the metatables of tables and user data
• Access to the registry
• Better user data
• Allow writing Lua binary modules in Rust