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