rust/src/libsyntax/visit.rs

// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.


use ast::*;
use codemap::span;

// Context-passing AST walker. Each overridden visit method has full control
// over what happens with its node, it can do its own traversal of the node's
// children (potentially passing in different contexts to each), call
// visit::visit_* to apply the default traversal algorithm (again, it can
// override the context), or prevent deeper traversal by doing nothing.

// Our typesystem doesn't do circular types, so the visitor record can not
// hold functions that take visitors. A vt enum is used to break the cycle.
enum vt<E> { mk_vt(visitor<E>), }

enum fn_kind {
    fk_item_fn(ident, ~[ty_param], purity), //< an item declared with fn()
    fk_method(ident, ~[ty_param], @method),
    fk_anon(Proto, capture_clause),  //< an anonymous function like fn@(...)
    fk_fn_block(capture_clause),     //< a block {||...}
    fk_dtor(~[ty_param], ~[attribute], node_id /* self id */,
            def_id /* parent class id */) // class destructor

}

fn name_of_fn(fk: fn_kind) -> ident {
    match fk {
      fk_item_fn(name, _, _) | fk_method(name, _, _) => {
          /* FIXME (#2543) */ copy name
      }
      fk_anon(*) | fk_fn_block(*) => parse::token::special_idents::anon,
      fk_dtor(*)                  => parse::token::special_idents::dtor
    }
}

fn tps_of_fn(fk: fn_kind) -> ~[ty_param] {
    match fk {
        fk_item_fn(_, tps, _) | fk_method(_, tps, _) |
        fk_dtor(tps, _, _, _) => {
            /* FIXME (#2543) */ copy tps
        }
        fk_anon(*) | fk_fn_block(*) => ~[]
    }
}

type visitor<E> =
    @{visit_mod: fn@(_mod, span, node_id, E, vt<E>),
      visit_view_item: fn@(@view_item, E, vt<E>),
      visit_foreign_item: fn@(@foreign_item, E, vt<E>),
      visit_item: fn@(@item, E, vt<E>),
      visit_local: fn@(@local, E, vt<E>),
      visit_block: fn@(ast::blk, E, vt<E>),
      visit_stmt: fn@(@stmt, E, vt<E>),
      visit_arm: fn@(arm, E, vt<E>),
      visit_pat: fn@(@pat, E, vt<E>),
      visit_decl: fn@(@decl, E, vt<E>),
      visit_expr: fn@(@expr, E, vt<E>),
      visit_expr_post: fn@(@expr, E, vt<E>),
      visit_ty: fn@(@Ty, E, vt<E>),
      visit_ty_params: fn@(~[ty_param], E, vt<E>),
      visit_fn: fn@(fn_kind, fn_decl, blk, span, node_id, E, vt<E>),
      visit_ty_method: fn@(ty_method, E, vt<E>),
      visit_trait_method: fn@(trait_method, E, vt<E>),
      visit_struct_def: fn@(@struct_def, ident, ~[ty_param], node_id, E,
                            vt<E>),
      visit_struct_field: fn@(@struct_field, E, vt<E>),
      visit_struct_method: fn@(@method, E, vt<E>)};

fn default_visitor<E>() -> visitor<E> {
    return @{visit_mod: |a,b,c,d,e|visit_mod::<E>(a, b, c, d, e),
          visit_view_item: |a,b,c|visit_view_item::<E>(a, b, c),
          visit_foreign_item: |a,b,c|visit_foreign_item::<E>(a, b, c),
          visit_item: |a,b,c|visit_item::<E>(a, b, c),
          visit_local: |a,b,c|visit_local::<E>(a, b, c),
          visit_block: |a,b,c|visit_block::<E>(a, b, c),
          visit_stmt: |a,b,c|visit_stmt::<E>(a, b, c),
          visit_arm: |a,b,c|visit_arm::<E>(a, b, c),
          visit_pat: |a,b,c|visit_pat::<E>(a, b, c),
          visit_decl: |a,b,c|visit_decl::<E>(a, b, c),
          visit_expr: |a,b,c|visit_expr::<E>(a, b, c),
          visit_expr_post: |_a,_b,_c| (),
          visit_ty: |a,b,c|skip_ty::<E>(a, b, c),
          visit_ty_params: |a,b,c|visit_ty_params::<E>(a, b, c),
          visit_fn: |a,b,c,d,e,f,g|visit_fn::<E>(a, b, c, d, e, f, g),
          visit_ty_method: |a,b,c|visit_ty_method::<E>(a, b, c),
          visit_trait_method: |a,b,c|visit_trait_method::<E>(a, b, c),
          visit_struct_def: |a,b,c,d,e,f|visit_struct_def::<E>(a, b, c,
                                                               d, e, f),
          visit_struct_field: |a,b,c|visit_struct_field::<E>(a, b, c),
          visit_struct_method: |a,b,c|visit_struct_method::<E>(a, b, c)};
}

fn visit_crate<E>(c: crate, e: E, v: vt<E>) {
    (v.visit_mod)(c.node.module, c.span, crate_node_id, e, v);
}

fn visit_mod<E>(m: _mod, _sp: span, _id: node_id, e: E, v: vt<E>) {
    for m.view_items.each |vi| { (v.visit_view_item)(*vi, e, v); }
    for m.items.each |i| { (v.visit_item)(*i, e, v); }
}

fn visit_view_item<E>(_vi: @view_item, _e: E, _v: vt<E>) { }

fn visit_local<E>(loc: @local, e: E, v: vt<E>) {
    (v.visit_pat)(loc.node.pat, e, v);
    (v.visit_ty)(loc.node.ty, e, v);
    match loc.node.init {
      None => (),
      Some(ex) => (v.visit_expr)(ex, e, v)
    }
}

fn visit_item<E>(i: @item, e: E, v: vt<E>) {
    match i.node {
      item_const(t, ex) => {
        (v.visit_ty)(t, e, v);
        (v.visit_expr)(ex, e, v);
      }
      item_fn(decl, purity, tp, ref body) => {
        (v.visit_fn)(fk_item_fn(/* FIXME (#2543) */ copy i.ident,
                              /* FIXME (#2543) */ copy tp,
                              purity), decl, (*body),
                   i.span, i.id, e, v);
      }
      item_mod(m) => (v.visit_mod)(m, i.span, i.id, e, v),
      item_foreign_mod(nm) => {
        for nm.view_items.each |vi| { (v.visit_view_item)(*vi, e, v); }
        for nm.items.each |ni| { (v.visit_foreign_item)(*ni, e, v); }
      }
      item_ty(t, tps) => {
        (v.visit_ty)(t, e, v);
        (v.visit_ty_params)(tps, e, v);
      }
      item_enum(ref enum_definition, tps) => {
        (v.visit_ty_params)(tps, e, v);
        visit_enum_def((*enum_definition), tps, e, v);
      }
      item_impl(tps, traits, ty, methods) => {
        (v.visit_ty_params)(tps, e, v);
        for traits.each |p| {
            visit_path(p.path, e, v);
        }
        (v.visit_ty)(ty, e, v);
        for methods.each |m| {
            visit_method_helper(*m, e, v)
        }
      }
      item_struct(struct_def, tps) => {
        (v.visit_ty_params)(tps, e, v);
        (v.visit_struct_def)(struct_def, i.ident, tps, i.id, e, v);
      }
      item_trait(tps, traits, ref methods) => {
        (v.visit_ty_params)(tps, e, v);
        for traits.each |p| { visit_path(p.path, e, v); }
        for (*methods).each |m| {
            (v.visit_trait_method)(*m, e, v);
        }
      }
      item_mac(ref m) => visit_mac((*m), e, v)
    }
}

fn visit_enum_def<E>(enum_definition: ast::enum_def, tps: ~[ast::ty_param],
                     e: E, v: vt<E>) {
    for enum_definition.variants.each |vr| {
        match vr.node.kind {
            tuple_variant_kind(variant_args) => {
                for variant_args.each |va| { (v.visit_ty)(va.ty, e, v); }
            }
            struct_variant_kind(struct_def) => {
                (v.visit_struct_def)(struct_def, vr.node.name, tps,
                                   vr.node.id, e, v);
            }
            enum_variant_kind(ref enum_definition) => {
                visit_enum_def((*enum_definition), tps, e, v);
            }
        }
        // Visit the disr expr if it exists
        vr.node.disr_expr.iter(|ex| (v.visit_expr)(*ex, e, v));
    }
}

fn skip_ty<E>(_t: @Ty, _e: E, _v: vt<E>) {}

fn visit_ty<E>(t: @Ty, e: E, v: vt<E>) {
    match t.node {
      ty_box(mt) | ty_uniq(mt) |
      ty_vec(mt) | ty_ptr(mt) | ty_rptr(_, mt) => {
        (v.visit_ty)(mt.ty, e, v);
      }
      ty_rec(ref flds) => for (*flds).each |f| {
        (v.visit_ty)(f.node.mt.ty, e, v);
      },
      ty_tup(ts) => for ts.each |tt| {
        (v.visit_ty)(*tt, e, v);
      },
      ty_fn(f) => {
        for f.decl.inputs.each |a| { (v.visit_ty)(a.ty, e, v); }
        visit_ty_param_bounds(f.bounds, e, v);
        (v.visit_ty)(f.decl.output, e, v);
      }
      ty_path(p, _) => visit_path(p, e, v),
      ty_fixed_length_vec(mt, _) => (v.visit_ty)(mt.ty, e, v),
      ty_nil |
      ty_bot |
      ty_mac(_) |
      ty_infer => ()
    }
}

fn visit_path<E>(p: @path, e: E, v: vt<E>) {
    for p.types.each |tp| { (v.visit_ty)(*tp, e, v); }
}

fn visit_pat<E>(p: @pat, e: E, v: vt<E>) {
    match p.node {
      pat_enum(path, children) => {
        visit_path(path, e, v);
        do option::iter(&children) |children| {
            for children.each |child| { (v.visit_pat)(*child, e, v); }}
      }
      pat_rec(fields, _) => for fields.each |f| {
        (v.visit_pat)(f.pat, e, v)
      },
      pat_struct(path, fields, _) => {
        visit_path(path, e, v);
        for fields.each |f| {
            (v.visit_pat)(f.pat, e, v);
        }
      }
      pat_tup(elts) => for elts.each |elt| {
        (v.visit_pat)(*elt, e, v)
      },
      pat_box(inner) | pat_uniq(inner) | pat_region(inner) =>
          (v.visit_pat)(inner, e, v),
      pat_ident(_, path, inner) => {
          visit_path(path, e, v);
          do option::iter(&inner) |subpat| { (v.visit_pat)(*subpat, e, v)};
      }
      pat_lit(ex) => (v.visit_expr)(ex, e, v),
      pat_range(e1, e2) => {
        (v.visit_expr)(e1, e, v);
        (v.visit_expr)(e2, e, v);
      }
      pat_wild => ()
    }
}

fn visit_foreign_item<E>(ni: @foreign_item, e: E, v: vt<E>) {
    match ni.node {
      foreign_item_fn(fd, _, tps) => {
        (v.visit_ty_params)(tps, e, v);
        visit_fn_decl(fd, e, v);
      }
      foreign_item_const(t) => {
        (v.visit_ty)(t, e, v);
      }
    }
}

fn visit_ty_param_bounds<E>(bounds: @~[ty_param_bound], e: E, v: vt<E>) {
    for vec::each(*bounds) |bound| {
        (v.visit_ty)(**bound, e, v)
    }
}

fn visit_ty_params<E>(tps: ~[ty_param], e: E, v: vt<E>) {
    for tps.each |tp| {
        visit_ty_param_bounds(tp.bounds, e, v);
    }
}

fn visit_fn_decl<E>(fd: fn_decl, e: E, v: vt<E>) {
    for fd.inputs.each |a| {
        (v.visit_pat)(a.pat, e, v);
        (v.visit_ty)(a.ty, e, v);
    }
    (v.visit_ty)(fd.output, e, v);
}

// Note: there is no visit_method() method in the visitor, instead override
// visit_fn() and check for fk_method().  I named this visit_method_helper()
// because it is not a default impl of any method, though I doubt that really
// clarifies anything. - Niko
fn visit_method_helper<E>(m: @method, e: E, v: vt<E>) {
    (v.visit_fn)(fk_method(/* FIXME (#2543) */ copy m.ident,
                         /* FIXME (#2543) */ copy m.tps, m),
               m.decl, m.body, m.span, m.id, e, v);
}

fn visit_struct_dtor_helper<E>(dtor: struct_dtor, tps: ~[ty_param],
                              parent_id: def_id, e: E, v: vt<E>) {
    (v.visit_fn)(fk_dtor(/* FIXME (#2543) */ copy tps, dtor.node.attrs,
                       dtor.node.self_id, parent_id), ast_util::dtor_dec(),
               dtor.node.body, dtor.span, dtor.node.id, e, v)

}

fn visit_fn<E>(fk: fn_kind, decl: fn_decl, body: blk, _sp: span,
               _id: node_id, e: E, v: vt<E>) {
    visit_fn_decl(decl, e, v);
    (v.visit_ty_params)(tps_of_fn(fk), e, v);
    (v.visit_block)(body, e, v);
}

fn visit_ty_method<E>(m: ty_method, e: E, v: vt<E>) {
    for m.decl.inputs.each |a| { (v.visit_ty)(a.ty, e, v); }
    (v.visit_ty_params)(m.tps, e, v);
    (v.visit_ty)(m.decl.output, e, v);
}

fn visit_trait_method<E>(m: trait_method, e: E, v: vt<E>) {
    match m {
      required(ref ty_m) => (v.visit_ty_method)((*ty_m), e, v),
      provided(m) => visit_method_helper(m, e, v)
    }
}

fn visit_struct_def<E>(sd: @struct_def, _nm: ast::ident, tps: ~[ty_param],
                       id: node_id, e: E, v: vt<E>) {
    for sd.fields.each |f| {
        (v.visit_struct_field)(*f, e, v);
    }
    do option::iter(&sd.dtor) |dtor| {
      visit_struct_dtor_helper(*dtor, tps, ast_util::local_def(id), e, v)
    };
}

fn visit_struct_field<E>(sf: @struct_field, e: E, v: vt<E>) {
    (v.visit_ty)(sf.node.ty, e, v);
}

fn visit_struct_method<E>(m: @method, e: E, v: vt<E>) {
    visit_method_helper(m, e, v);
}

fn visit_block<E>(b: ast::blk, e: E, v: vt<E>) {
    for b.node.view_items.each |vi| {
        (v.visit_view_item)(*vi, e, v);
    }
    for b.node.stmts.each |s| {
        (v.visit_stmt)(*s, e, v);
    }
    visit_expr_opt(b.node.expr, e, v);
}

fn visit_stmt<E>(s: @stmt, e: E, v: vt<E>) {
    match s.node {
      stmt_decl(d, _) => (v.visit_decl)(d, e, v),
      stmt_expr(ex, _) => (v.visit_expr)(ex, e, v),
      stmt_semi(ex, _) => (v.visit_expr)(ex, e, v),
      stmt_mac(ref mac, _) => visit_mac((*mac), e, v)
    }
}

fn visit_decl<E>(d: @decl, e: E, v: vt<E>) {
    match d.node {
      decl_local(locs) => for locs.each |loc| {
        (v.visit_local)(*loc, e, v)
      },
      decl_item(it) => (v.visit_item)(it, e, v)
    }
}

fn visit_expr_opt<E>(eo: Option<@expr>, e: E, v: vt<E>) {
    match eo { None => (), Some(ex) => (v.visit_expr)(ex, e, v) }
}

fn visit_exprs<E>(exprs: ~[@expr], e: E, v: vt<E>) {
    for exprs.each |ex| { (v.visit_expr)(*ex, e, v); }
}

fn visit_mac<E>(_m: mac, _e: E, _v: vt<E>) {
    /* no user-serviceable parts inside */
}

fn visit_expr<E>(ex: @expr, e: E, v: vt<E>) {
    match ex.node {
      expr_vstore(x, _) => (v.visit_expr)(x, e, v),
      expr_vec(es, _) => visit_exprs(es, e, v),
      expr_repeat(element, count, _) => {
        (v.visit_expr)(element, e, v);
        (v.visit_expr)(count, e, v);
      }
      expr_rec(ref flds, base) => {
        for (*flds).each |f| { (v.visit_expr)(f.node.expr, e, v); }
        visit_expr_opt(base, e, v);
      }
      expr_struct(p, ref flds, base) => {
        visit_path(p, e, v);
        for (*flds).each |f| { (v.visit_expr)(f.node.expr, e, v); }
        visit_expr_opt(base, e, v);
      }
      expr_tup(elts) => for elts.each |el| { (v.visit_expr)(*el, e, v); },
      expr_call(callee, args, _) => {
        visit_exprs(args, e, v);
        (v.visit_expr)(callee, e, v);
      }
      expr_method_call(callee, _, tys, args, _) => {
        visit_exprs(args, e, v);
        for tys.each |tp| { (v.visit_ty)(*tp, e, v); }
        (v.visit_expr)(callee, e, v);
      }
      expr_binary(_, a, b) => {
        (v.visit_expr)(a, e, v); (v.visit_expr)(b, e, v);
      }
      expr_addr_of(_, x) | expr_unary(_, x) |
      expr_loop_body(x) | expr_do_body(x) |
      expr_assert(x) => (v.visit_expr)(x, e, v),
      expr_lit(_) => (),
      expr_cast(x, t) => { (v.visit_expr)(x, e, v); (v.visit_ty)(t, e, v); }
      expr_if(x, ref b, eo) => {
        (v.visit_expr)(x, e, v);
        (v.visit_block)((*b), e, v);
        visit_expr_opt(eo, e, v);
      }
      expr_while(x, ref b) => {
        (v.visit_expr)(x, e, v);
        (v.visit_block)((*b), e, v);
      }
      expr_loop(ref b, _) => (v.visit_block)((*b), e, v),
      expr_match(x, ref arms) => {
        (v.visit_expr)(x, e, v);
        for (*arms).each |a| { (v.visit_arm)(*a, e, v); }
      }
      expr_fn(proto, decl, ref body, cap_clause) => {
        (v.visit_fn)(fk_anon(proto, cap_clause), decl, (*body),
                     ex.span, ex.id, e, v);
      }
      expr_fn_block(decl, ref body, cap_clause) => {
        (v.visit_fn)(fk_fn_block(cap_clause), decl, (*body),
                     ex.span, ex.id, e, v);
      }
      expr_block(ref b) => (v.visit_block)((*b), e, v),
      expr_assign(a, b) => {
        (v.visit_expr)(b, e, v);
        (v.visit_expr)(a, e, v);
      }
      expr_copy(a) => (v.visit_expr)(a, e, v),
      expr_unary_move(a) => (v.visit_expr)(a, e, v),
      expr_swap(a, b) => { (v.visit_expr)(a, e, v); (v.visit_expr)(b, e, v); }
      expr_assign_op(_, a, b) => {
        (v.visit_expr)(b, e, v);
        (v.visit_expr)(a, e, v);
      }
      expr_field(x, _, tys) => {
        (v.visit_expr)(x, e, v);
        for tys.each |tp| { (v.visit_ty)(*tp, e, v); }
      }
      expr_index(a, b) => {
        (v.visit_expr)(a, e, v);
        (v.visit_expr)(b, e, v);
      }
      expr_path(p) => visit_path(p, e, v),
      expr_fail(eo) => visit_expr_opt(eo, e, v),
      expr_break(_) => (),
      expr_again(_) => (),
      expr_ret(eo) => visit_expr_opt(eo, e, v),
      expr_log(_, lv, x) => {
        (v.visit_expr)(lv, e, v);
        (v.visit_expr)(x, e, v);
      }
      expr_mac(ref mac) => visit_mac((*mac), e, v),
      expr_paren(x) => (v.visit_expr)(x, e, v),
    }
    (v.visit_expr_post)(ex, e, v);
}

fn visit_arm<E>(a: arm, e: E, v: vt<E>) {
    for a.pats.each |p| { (v.visit_pat)(*p, e, v); }
    visit_expr_opt(a.guard, e, v);
    (v.visit_block)(a.body, e, v);
}

// Simpler, non-context passing interface. Always walks the whole tree, simply
// calls the given functions on the nodes.

type simple_visitor =
    @{visit_mod: fn@(_mod, span, node_id),
      visit_view_item: fn@(@view_item),
      visit_foreign_item: fn@(@foreign_item),
      visit_item: fn@(@item),
      visit_local: fn@(@local),
      visit_block: fn@(ast::blk),
      visit_stmt: fn@(@stmt),
      visit_arm: fn@(arm),
      visit_pat: fn@(@pat),
      visit_decl: fn@(@decl),
      visit_expr: fn@(@expr),
      visit_expr_post: fn@(@expr),
      visit_ty: fn@(@Ty),
      visit_ty_params: fn@(~[ty_param]),
      visit_fn: fn@(fn_kind, fn_decl, blk, span, node_id),
      visit_ty_method: fn@(ty_method),
      visit_trait_method: fn@(trait_method),
      visit_struct_def: fn@(@struct_def, ident, ~[ty_param], node_id),
      visit_struct_field: fn@(@struct_field),
      visit_struct_method: fn@(@method)};

fn simple_ignore_ty(_t: @Ty) {}

fn default_simple_visitor() -> simple_visitor {
    return @{visit_mod: fn@(_m: _mod, _sp: span, _id: node_id) { },
          visit_view_item: fn@(_vi: @view_item) { },
          visit_foreign_item: fn@(_ni: @foreign_item) { },
          visit_item: fn@(_i: @item) { },
          visit_local: fn@(_l: @local) { },
          visit_block: fn@(_b: ast::blk) { },
          visit_stmt: fn@(_s: @stmt) { },
          visit_arm: fn@(_a: arm) { },
          visit_pat: fn@(_p: @pat) { },
          visit_decl: fn@(_d: @decl) { },
          visit_expr: fn@(_e: @expr) { },
          visit_expr_post: fn@(_e: @expr) { },
          visit_ty: simple_ignore_ty,
          visit_ty_params: fn@(_ps: ~[ty_param]) {},
          visit_fn: fn@(_fk: fn_kind, _d: fn_decl, _b: blk, _sp: span,
                        _id: node_id) { },
          visit_ty_method: fn@(_m: ty_method) { },
          visit_trait_method: fn@(_m: trait_method) { },
          visit_struct_def: fn@(_sd: @struct_def, _nm: ident,
                                _tps: ~[ty_param], _id: node_id) { },
          visit_struct_field: fn@(_f: @struct_field) { },
          visit_struct_method: fn@(_m: @method) { }
         };
}

fn mk_simple_visitor(v: simple_visitor) -> vt<()> {
    fn v_mod(f: fn@(_mod, span, node_id), m: _mod, sp: span, id: node_id,
             &&e: (), v: vt<()>) {
        f(m, sp, id);
        visit_mod(m, sp, id, e, v);
    }
    fn v_view_item(f: fn@(@view_item), vi: @view_item, &&e: (), v: vt<()>) {
        f(vi);
        visit_view_item(vi, e, v);
    }
    fn v_foreign_item(f: fn@(@foreign_item), ni: @foreign_item, &&e: (),
                     v: vt<()>) {
        f(ni);
        visit_foreign_item(ni, e, v);
    }
    fn v_item(f: fn@(@item), i: @item, &&e: (), v: vt<()>) {
        f(i);
        visit_item(i, e, v);
    }
    fn v_local(f: fn@(@local), l: @local, &&e: (), v: vt<()>) {
        f(l);
        visit_local(l, e, v);
    }
    fn v_block(f: fn@(ast::blk), bl: ast::blk, &&e: (), v: vt<()>) {
        f(bl);
        visit_block(bl, e, v);
    }
    fn v_stmt(f: fn@(@stmt), st: @stmt, &&e: (), v: vt<()>) {
        f(st);
        visit_stmt(st, e, v);
    }
    fn v_arm(f: fn@(arm), a: arm, &&e: (), v: vt<()>) {
        f(a);
        visit_arm(a, e, v);
    }
    fn v_pat(f: fn@(@pat), p: @pat, &&e: (), v: vt<()>) {
        f(p);
        visit_pat(p, e, v);
    }
    fn v_decl(f: fn@(@decl), d: @decl, &&e: (), v: vt<()>) {
        f(d);
        visit_decl(d, e, v);
    }
    fn v_expr(f: fn@(@expr), ex: @expr, &&e: (), v: vt<()>) {
        f(ex);
        visit_expr(ex, e, v);
    }
    fn v_expr_post(f: fn@(@expr), ex: @expr, &&_e: (), _v: vt<()>) {
        f(ex);
    }
    fn v_ty(f: fn@(@Ty), ty: @Ty, &&e: (), v: vt<()>) {
        f(ty);
        visit_ty(ty, e, v);
    }
    fn v_ty_method(f: fn@(ty_method), ty: ty_method, &&e: (), v: vt<()>) {
        f(ty);
        visit_ty_method(ty, e, v);
    }
    fn v_trait_method(f: fn@(trait_method), m: trait_method, &&e: (),
                      v: vt<()>) {
        f(m);
        visit_trait_method(m, e, v);
    }
    fn v_struct_def(f: fn@(@struct_def, ident, ~[ty_param], node_id),
                    sd: @struct_def, nm: ident, tps: ~[ty_param], id: node_id,
                    &&e: (), v: vt<()>) {
        f(sd, nm, tps, id);
        visit_struct_def(sd, nm, tps, id, e, v);
    }
    fn v_ty_params(f: fn@(~[ty_param]),
                   ps: ~[ty_param],
                   &&e: (), v: vt<()>) {
        f(ps);
        visit_ty_params(ps, e, v);
    }
    fn v_fn(f: fn@(fn_kind, fn_decl, blk, span, node_id),
            fk: fn_kind, decl: fn_decl, body: blk, sp: span,
            id: node_id, &&e: (), v: vt<()>) {
        f(fk, decl, body, sp, id);
        visit_fn(fk, decl, body, sp, id, e, v);
    }
    let visit_ty = |a,b,c| v_ty(v.visit_ty, a, b, c);
    fn v_struct_field(f: fn@(@struct_field), sf: @struct_field, &&e: (),
                      v: vt<()>) {
        f(sf);
        visit_struct_field(sf, e, v);
    }
    fn v_struct_method(f: fn@(@method), m: @method, &&e: (), v: vt<()>) {
        f(m);
        visit_struct_method(m, e, v);
    }
    return mk_vt(@{visit_mod: |a,b,c,d,e|v_mod(v.visit_mod, a, b, c, d, e),
                visit_view_item: |a,b,c|
                    v_view_item(v.visit_view_item, a, b, c),
                visit_foreign_item:
                    |a,b,c|v_foreign_item(v.visit_foreign_item, a, b, c),
                visit_item: |a,b,c|v_item(v.visit_item, a, b, c),
                visit_local: |a,b,c|v_local(v.visit_local, a, b, c),
                visit_block: |a,b,c|v_block(v.visit_block, a, b, c),
                visit_stmt: |a,b,c|v_stmt(v.visit_stmt, a, b, c),
                visit_arm: |a,b,c|v_arm(v.visit_arm, a, b, c),
                visit_pat: |a,b,c|v_pat(v.visit_pat, a, b, c),
                visit_decl: |a,b,c|v_decl(v.visit_decl, a, b, c),
                visit_expr: |a,b,c|v_expr(v.visit_expr, a, b, c),
                visit_expr_post: |a,b,c| v_expr_post(v.visit_expr_post,
                                                     a, b, c),
                visit_ty: visit_ty,
                visit_ty_params: |a,b,c|
                    v_ty_params(v.visit_ty_params, a, b, c),
                visit_fn: |a,b,c,d,e,f,g|
                    v_fn(v.visit_fn, a, b, c, d, e, f, g),
                visit_ty_method: |a,b,c|
                    v_ty_method(v.visit_ty_method, a, b, c),
                visit_trait_method: |a,b,c|
                    v_trait_method(v.visit_trait_method, a, b, c),
                visit_struct_def: |a,b,c,d,e,f|
                    v_struct_def(v.visit_struct_def, a, b, c, d, e, f),
                visit_struct_field: |a,b,c|
                    v_struct_field(v.visit_struct_field, a, b, c),
                visit_struct_method: |a,b,c|
                    v_struct_method(v.visit_struct_method, a, b, c)
               });
}

// Local Variables:
// mode: rust
// fill-column: 78;
// indent-tabs-mode: nil
// c-basic-offset: 4
// buffer-file-coding-system: utf-8-unix
// End: