gistfile1.txt

////////////////////
// in visit.rs:

trait Visitor {
  fn visit_item(&mut self, item: @ast::item) { ... }
  fn visit_expr(&mut self, expr: @ast::expr) { visit_expr(self, expr); }
  ...
}

// default implementations:
fn visit_expr<V:Visitor>(&mut V, expr: @ast::Expr) {...}

////////////////////
// in somewhere else:

pub struct MyContext {
  ...
}

impl Visitor for MyContext {
  fn visit_expr(&mut self, expr: @ast::expr) {
    visit::visit_expr(self, expr); // visit sub-expressions

    match expr.node {
    }
  }
}