beatles transcript

% rustc goodbye.rs && rustc -L . beatles.rs && ./beatles
goodbye.rs:10:25: 10:29 warning: unused import, #[warn(unused_imports)] on by default
goodbye.rs:10 use syntax::ext::base::{self, ExtCtxt, MacResult, DummyResult, MacEager};
                                      ^~~~
I don't know why you say goodbye, I say hello

beatles.rs

#![feature(plugin)]
#![plugin(goodbye)]

macro_rules! beatles {
    ($fmt:tt, $($arg:tt)*) => {
        println!(concat!(goodbye!($fmt), $fmt), $($arg)*)
    }
}

fn main() {
    beatles!("{} hello", "I don't know why you say", ", I say"); 
}

demo f1 expanded.rs

fn f1() { let _s = "Goodbye {}"; }

demo.rs

#![feature(plugin)]
#![plugin(goodbye)]

fn main() {
    f1();
    f2();
    f3();
}

fn f1() {
    let _s = goodbye!("Hello {}");
}

fn f2() {
    println!(goodbye!("Hello {}"), 2);
}

fn f3() {
    macro_rules! gprintln {
        ($fmt:tt, $($arg:tt)*) => {
            println!(goodbye!($fmt), $($arg)*)
        }
    }

    gprintln!("Hello {}", 3);
}

goodbye.rs

#![crate_type="dylib"]
#![feature(plugin_registrar, rustc_private)]

extern crate syntax;
extern crate rustc;

use syntax::codemap::Span;
use syntax::parse::token;
use syntax::ast::{TokenTree, TtToken};
use syntax::ext::base::{self, ExtCtxt, MacResult, DummyResult, MacEager};
use syntax::ext::build::AstBuilder;  // trait for expr_usize
use rustc::plugin::Registry;

fn expand_goodbye(cx: &mut ExtCtxt, sp: Span, args: &[TokenTree]) -> Box<MacResult + 'static> {
    let name = match args {
        [TtToken(_, token::Literal(token::Lit::Str_(name), _opt_name))] |
        [TtToken(_, token::Literal(token::Lit::StrRaw(name, _ /* hash count */), _opt_name))]
            => name,
        ref t => {
            cx.span_err(sp, &format!("argument should be a single token, got {:?}", t));
            return DummyResult::any(sp);
        }
    };

    let new_text = token::get_name(name)
        .replace("hello", "goodbye")
        .replace("Hello", "Goodbye")
        .replace("HELLO", "GOODBYE");

    MacEager::expr(cx.expr_str(sp, token::get_name(token::intern(&new_text))))
}

#[plugin_registrar]
pub fn plugin_registrar(reg: &mut Registry) {
    reg.register_macro("goodbye", expand_goodbye);
}