fabricedesre / aster

A libsyntax ast builder

Rust Syntax Ast Builder

Aster is a framework that simplifies generating Rust AST. It supports using syntex with stable Rust, and the builtin libsyntax with the nightly Rust.

Example

This example demonstrates how to use Aster to create a simple compound expression. We will take advantage of Cargo features to optionally switch between the two different backends. Let's start with the Cargo.toml file:

[package]
name = "hello_world"
version = "0.3.0"
authors = ["Erick Tryzelaar <[e-mail]>"]

[features]
default = ["aster/default", "syntex_syntax"]
nightly = ["aster/nightly"]

[dependencies]
aster = { version = "*", default_features = false }
syntex_syntax = { version = "*", optional = true }

Here is the actual script:

#![cfg_attr(feature = "nightly", feature(rustc_private))]

extern crate aster as aster_lib;

#[cfg(feature = "nightly")]
use aster_lib::syntax as aster;

#[cfg(not(feature = "nightly"))]
use aster_lib::syntex as aster;

fn main() {
    let builder = aster::AstBuilder::new();

    let expr = builder.expr()
        .add().u32(1).u32(2);

    // prints `1 + 2`.
    println!(
        "{}",
        // Aster re-exports the syntax library to simplify it's use.
        aster::syntax::print::pprust::expr_to_string(&expr));
}

When run with cargo run, the example will use syntex. With cargo run --no-default-features --features nightly, it will use libsyntax.