Rust Syntax Ast Builder
=======================
[](https://travis-ci.org/serde-rs/aster)
[](https://crates.io/crates/aster)
Aster is a framework that simplifies generating Rust AST. It supports using
[syntex](https://github.com/erickt/rust-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](http://doc.crates.io/manifest.html#the-[features]-section) to
optionally switch between the two different backends. Let's start with the
`Cargo.toml` file:
```toml
[package]
name = "hello_world"
version = "0.3.0"
authors = ["Erick Tryzelaar <erick.tryzelaar@gmail.com>"]
[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:
```rust
#![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.