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 core::prelude::*;

use abi::AbiSet;
use ast::*;
use ast;
use codemap::span;
use parse;
use opt_vec;
use opt_vec::OptVec;

// 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.
//
// Note: it is an important invariant that the default visitor walks the body
// of a function in "execution order" (more concretely, reverse post-order
// with respect to the CFG implied by the AST), meaning that if AST node A may
// execute before AST node B, then A is visited first.  The borrow checker in
// particular relies on this property.

// 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.
pub enum vt<E> { mk_vt(visitor<E>), }

pub enum fn_kind<'self> {
    // fn foo() or extern "Abi" fn foo()
    fk_item_fn(ident, &'self Generics, purity, AbiSet),

    // fn foo(&self)
    fk_method(ident, &'self Generics, &'self method),

    // fn@(x, y) { ... }
    fk_anon(ast::Sigil),

    // |x, y| ...
    fk_fn_block,
}

pub fn name_of_fn(fk: &fn_kind) -> ident {
    match *fk {
      fk_item_fn(name, _, _, _) | fk_method(name, _, _) => {
          name
      }
      fk_anon(*) | fk_fn_block(*) => parse::token::special_idents::anon,
    }
}

pub fn generics_of_fn(fk: &fn_kind) -> Generics {
    match *fk {
        fk_item_fn(_, generics, _, _) |
        fk_method(_, generics, _) => {
            copy *generics
        }
        fk_anon(*) | fk_fn_block(*) => {
            Generics {
                lifetimes: opt_vec::Empty,
                ty_params: opt_vec::Empty,
            }
        }
    }
}

pub struct 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(&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_generics: @fn(&Generics, 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, &Generics, node_id, E, vt<E>),
    visit_struct_field: @fn(@struct_field, E, vt<E>),
    visit_struct_method: @fn(@method, E, vt<E>)
}

pub type visitor<E> = @Visitor<E>;

pub fn default_visitor<E: Copy>() -> visitor<E> {
    return @Visitor {
        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_generics: |a,b,c|visit_generics::<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)
    };
}

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

pub fn visit_mod<E: Copy>(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); }
}

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

pub fn visit_local<E: Copy>(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_trait_ref<E: Copy>(tref: @ast::trait_ref, e: E, v: vt<E>) {
    visit_path(tref.path, e, v);
}

pub fn visit_item<E: Copy>(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(ref decl, purity, abi, ref generics, ref body) => {
            (v.visit_fn)(
                &fk_item_fn(
                    i.ident,
                    generics,
                    purity,
                    abi
                ),
                decl,
                body,
                i.span,
                i.id,
                e,
                v
            );
        }
        item_mod(ref m) => (v.visit_mod)(m, i.span, i.id, e, v),
        item_foreign_mod(ref 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, ref tps) => {
            (v.visit_ty)(t, e, v);
            (v.visit_generics)(tps, e, v);
        }
        item_enum(ref enum_definition, ref tps) => {
            (v.visit_generics)(tps, e, v);
            visit_enum_def(
                enum_definition,
                tps,
                e,
                v
            );
        }
        item_impl(ref tps, ref traits, ty, ref methods) => {
            (v.visit_generics)(tps, e, v);
            for traits.each |&p| {
                visit_trait_ref(p, e, v);
            }
            (v.visit_ty)(ty, e, v);
            for methods.each |m| {
                visit_method_helper(*m, e, v)
            }
        }
        item_struct(struct_def, ref generics) => {
            (v.visit_generics)(generics, e, v);
            (v.visit_struct_def)(struct_def, i.ident, generics, i.id, e, v);
        }
        item_trait(ref generics, ref traits, ref methods) => {
            (v.visit_generics)(generics, 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)
    }
}

pub fn visit_enum_def<E: Copy>(enum_definition: &ast::enum_def,
                               tps: &Generics,
                               e: E,
                               v: vt<E>) {
    for enum_definition.variants.each |vr| {
        match vr.node.kind {
            tuple_variant_kind(ref 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);
            }
        }
        // Visit the disr expr if it exists
        for vr.node.disr_expr.each |ex| { (v.visit_expr)(*ex, e, v) }
    }
}

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

pub fn visit_ty<E: Copy>(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_tup(ref ts) => {
            for ts.each |tt| {
                (v.visit_ty)(*tt, e, v);
            }
        },
        ty_closure(ref f) => {
            for f.decl.inputs.each |a| { (v.visit_ty)(a.ty, e, v); }
            (v.visit_ty)(f.decl.output, e, v);
        },
        ty_bare_fn(ref f) => {
            for f.decl.inputs.each |a| { (v.visit_ty)(a.ty, e, v); }
            (v.visit_ty)(f.decl.output, e, v);
        },
        ty_path(p, _) => visit_path(p, e, v),
        ty_fixed_length_vec(ref mt, ex) => {
            (v.visit_ty)(mt.ty, e, v);
            (v.visit_expr)(ex, e, v);
        },
        ty_nil | ty_bot | ty_mac(_) | ty_infer => ()
    }
}

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

pub fn visit_pat<E: Copy>(p: @pat, e: E, v: vt<E>) {
    match p.node {
        pat_enum(path, ref children) => {
            visit_path(path, e, v);
            for children.each |children| {
                for children.each |child| { (v.visit_pat)(*child, e, v); }
            }
        }
        pat_struct(path, ref fields, _) => {
            visit_path(path, e, v);
            for fields.each |f| {
                (v.visit_pat)(f.pat, e, v);
            }
        }
        pat_tup(ref 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, ref inner) => {
            visit_path(path, e, v);
            for inner.each |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 => (),
        pat_vec(ref before, ref slice, ref after) => {
            for before.each |elt| {
                (v.visit_pat)(*elt, e, v);
            }
            for slice.each |elt| {
                (v.visit_pat)(*elt, e, v);
            }
            for after.each |tail| {
                (v.visit_pat)(*tail, e, v);
            }
        }
    }
}

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

pub fn visit_ty_param_bounds<E: Copy>(bounds: @OptVec<TyParamBound>,
                                      e: E, v: vt<E>) {
    for bounds.each |bound| {
        match *bound {
            TraitTyParamBound(ty) => visit_trait_ref(ty, e, v),
            RegionTyParamBound => {}
        }
    }
}

pub fn visit_generics<E: Copy>(generics: &Generics, e: E, v: vt<E>) {
    for generics.ty_params.each |tp| {
        visit_ty_param_bounds(tp.bounds, e, v);
    }
}

pub fn visit_fn_decl<E: Copy>(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
pub fn visit_method_helper<E: Copy>(m: &method, e: E, v: vt<E>) {
    (v.visit_fn)(
        &fk_method(
            /* FIXME (#2543) */ copy m.ident,
            &m.generics,
            m
        ),
        &m.decl,
        &m.body,
        m.span,
        m.id,
        e,
        v
    );
}

pub fn visit_fn<E: Copy>(fk: &fn_kind, decl: &fn_decl, body: &blk, _sp: span,
                         _id: node_id, e: E, v: vt<E>) {
    visit_fn_decl(decl, e, v);
    let generics = generics_of_fn(fk);
    (v.visit_generics)(&generics, e, v);
    (v.visit_block)(body, e, v);
}

pub fn visit_ty_method<E: Copy>(m: &ty_method, e: E, v: vt<E>) {
    for m.decl.inputs.each |a| { (v.visit_ty)(a.ty, e, v); }
    (v.visit_generics)(&m.generics, e, v);
    (v.visit_ty)(m.decl.output, e, v);
}

pub fn visit_trait_method<E: Copy>(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)
    }
}

pub fn visit_struct_def<E: Copy>(
    sd: @struct_def,
    _nm: ast::ident,
    _generics: &Generics,
    _id: node_id,
    e: E,
    v: vt<E>
) {
    for sd.fields.each |f| {
        (v.visit_struct_field)(*f, e, v);
    }
}

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

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

pub fn visit_block<E: Copy>(b: &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);
}

pub 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)
    }
}

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

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

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

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

pub fn visit_expr<E: Copy>(ex: @expr, e: E, v: vt<E>) {
    match ex.node {
        expr_vstore(x, _) => (v.visit_expr)(x, e, v),
        expr_vec(ref es, _) => visit_exprs(*es, e, v),
        expr_repeat(element, count, _) => {
            (v.visit_expr)(element, e, v);
            (v.visit_expr)(count, 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(ref elts) => {
            for elts.each |el| { (v.visit_expr)(*el, e, v) }
        }
        expr_call(callee, ref args, _) => {
            visit_exprs(*args, e, v);
            (v.visit_expr)(callee, e, v);
        }
        expr_method_call(callee, _, ref tys, ref 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) => (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_block(ref decl, ref body) => {
            (v.visit_fn)(
                &fk_fn_block,
                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_assign_op(_, a, b) => {
            (v.visit_expr)(b, e, v);
            (v.visit_expr)(a, e, v);
        }
        expr_field(x, _, ref 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_self => (),
        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),
        expr_inline_asm(ref a) => {
            for a.inputs.each |&(_, in)| {
                (v.visit_expr)(in, e, v);
            }
            for a.outputs.each |&(_, out)| {
                (v.visit_expr)(out, e, v);
            }
        }
    }
    (v.visit_expr_post)(ex, e, v);
}

pub fn visit_arm<E: Copy>(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.

pub struct SimpleVisitor {
    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(&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_generics: @fn(&Generics),
    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, &Generics, node_id),
    visit_struct_field: @fn(@struct_field),
    visit_struct_method: @fn(@method)
}

pub type simple_visitor = @SimpleVisitor;

pub fn simple_ignore_ty(_t: @Ty) {}

pub fn default_simple_visitor() -> @SimpleVisitor {
    @SimpleVisitor {
        visit_mod: |_m, _sp, _id| { },
        visit_view_item: |_vi| { },
        visit_foreign_item: |_ni| { },
        visit_item: |_i| { },
        visit_local: |_l| { },
        visit_block: |_b| { },
        visit_stmt: |_s| { },
        visit_arm: |_a| { },
        visit_pat: |_p| { },
        visit_decl: |_d| { },
        visit_expr: |_e| { },
        visit_expr_post: |_e| { },
        visit_ty: simple_ignore_ty,
        visit_generics: |_| {},
        visit_fn: |_, _, _, _, _| {},
        visit_ty_method: |_| {},
        visit_trait_method: |_| {},
        visit_struct_def: |_, _, _, _| {},
        visit_struct_field: |_| {},
        visit_struct_method: |_| {},
    }
}

pub 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, &Generics, node_id),
        sd: @struct_def,
        nm: ident,
        generics: &Generics,
        id: node_id,
        e: (),
        v: vt<()>
    ) {
        f(sd, nm, generics, id);
        visit_struct_def(sd, nm, generics, id, e, v);
    }
    fn v_generics(
        f: @fn(&Generics),
        ps: &Generics,
        e: (),
        v: vt<()>
    ) {
        f(ps);
        visit_generics(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: @fn(@Ty, x: (), vt<()>) =
        |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(@Visitor {
        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_generics: |a,b,c|
            v_generics(v.visit_generics, 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)
    });
}