rust/src/comp/middle/fold.rs

import std.map.hashmap;
import util.common.new_str_hash;
import util.common.spanned;
import util.common.span;
import util.common.option;
import util.common.some;
import util.common.none;
import util.common.ty_mach;


import front.ast;
import front.ast.ident;
import front.ast.name;
import front.ast.path;
import front.ast.ty;
import front.ast.expr;
import front.ast.lval;
import front.ast.stmt;
import front.ast.block;
import front.ast.item;
import front.ast.slot;
import front.ast.decl;
import front.ast.referent;

import std._vec;

type ast_fold[ENV] =
    @rec
    (
     // Name fold.
     (fn(&ENV e, &span sp, ast.name_ n) -> name)  fold_name,

     // Type folds.
     (fn(&ENV e, &span sp) -> @ty)                fold_ty_nil,
     (fn(&ENV e, &span sp) -> @ty)                fold_ty_bool,
     (fn(&ENV e, &span sp) -> @ty)                fold_ty_int,
     (fn(&ENV e, &span sp) -> @ty)                fold_ty_uint,
     (fn(&ENV e, &span sp, ty_mach tm) -> @ty)    fold_ty_machine,
     (fn(&ENV e, &span sp) -> @ty)                fold_ty_char,
     (fn(&ENV e, &span sp) -> @ty)                fold_ty_str,
     (fn(&ENV e, &span sp, @ty t) -> @ty)         fold_ty_box,
     (fn(&ENV e, &span sp, @ty t) -> @ty)         fold_ty_vec,

     (fn(&ENV e, &span sp,
         vec[tup(bool, @ty)] elts) -> @ty)        fold_ty_tup,

     (fn(&ENV e, &span sp, ast.path p,
         &option[referent] r) -> @ty)             fold_ty_path,

     // Expr folds.
     (fn(&ENV e, &span sp,
         vec[@expr] es) -> @expr)                 fold_expr_vec,

     (fn(&ENV e, &span sp,
         vec[tup(bool,@expr)] es) -> @expr)       fold_expr_tup,

     (fn(&ENV e, &span sp,
         vec[tup(ident,@expr)] fields) -> @expr)  fold_expr_rec,

     (fn(&ENV e, &span sp,
         @expr f, vec[@expr] args) -> @expr)      fold_expr_call,

     (fn(&ENV e, &span sp,
         ast.binop,
         @expr lhs, @expr rhs) -> @expr)          fold_expr_binary,

     (fn(&ENV e, &span sp,
         ast.unop, @expr e) -> @expr)             fold_expr_unary,

     (fn(&ENV e, &span sp,
         @ast.lit) -> @expr)                      fold_expr_lit,

     (fn(&ENV e, &span sp,
         @expr cond, block thn,
         &option[block] els) -> @expr)            fold_expr_if,

     (fn(&ENV e, &span sp,
         block blk) -> @expr)                     fold_expr_block,

     (fn(&ENV e, &span sp,
         @lval lhs, @expr rhs) -> @expr)          fold_expr_assign,

     (fn(&ENV e, &span sp,
         @lval lv) -> @expr)                      fold_expr_lval,

     // Lvalue folds.
     (fn(&ENV e, &span sp,
         @expr e, ident i) -> @lval)              fold_lval_field,

     (fn(&ENV e, &span sp,
         @expr e, @expr ix) -> @lval)             fold_lval_index,

     (fn(&ENV e, &span sp,
         &name n,
         &option[referent] r) -> @lval)           fold_lval_name,

     // Decl folds.
     (fn(&ENV e, &span sp,
         ident ident, &option[@ty] ty,
         &option[@expr]) -> @decl)                fold_decl_local,

     (fn(&ENV e, &span sp,
         ident ident, @item item) -> @decl)        fold_decl_item,


     // Stmt folds.
     (fn(&ENV e, &span sp,
         @decl decl) -> @stmt)                    fold_stmt_decl,

     (fn(&ENV e, &span sp,
         &option[@expr] rv) -> @stmt)             fold_stmt_ret,

     (fn(&ENV e, &span sp,
         @expr e) -> @stmt)                       fold_stmt_log,

     (fn(&ENV e, &span sp,
         @expr e) -> @stmt)                       fold_stmt_expr,

     // Item folds.
     (fn(&ENV e, &span sp,
         &ast._fn f, ast.item_id id) -> @item)    fold_item_fn,

     (fn(&ENV e, &span sp,
         &ast._mod m) -> @item)                   fold_item_mod,

     (fn(&ENV e, &span sp,
         @ty t, ast.item_id id) -> @item)         fold_item_ty,

     // Additional nodes.
     (fn(&ENV e, &span sp,
         vec[@stmt] stmts) -> block)              fold_block,

     (fn(&ENV e, vec[ast.input] inputs,
         &ty output, block body) -> ast._fn)      fold_fn,

     (fn(&ENV e, &ast._mod m) -> ast._mod)        fold_mod,

     (fn(&ENV e, &span sp,
         &ast._mod m) -> @ast.crate)              fold_crate,

     // Env updates.
     (fn(&ENV e, @ast.crate c) -> ENV) update_env_for_crate,
     (fn(&ENV e, @item i) -> ENV) update_env_for_item,
     (fn(&ENV e, @stmt s) -> ENV) update_env_for_stmt,
     (fn(&ENV e, @decl i) -> ENV) update_env_for_decl,
     (fn(&ENV e, @lval l) -> ENV) update_env_for_lval,
     (fn(&ENV e, @expr x) -> ENV) update_env_for_expr,
     (fn(&ENV e, @ty t) -> ENV) update_env_for_ty,

     // Traversal control.
     (fn(&ENV v) -> bool) keep_going
     );


//// Fold drivers.

fn fold_name[ENV](&ENV env, ast_fold[ENV] fld, &name n) -> name {
    let vec[@ast.ty] tys_ = vec();
    for (@ast.ty t in n.node.types) {
        append[@ast.ty](tys_, fold_ty(env, fld, t));
    }
    let ast.name_ n_ = rec(ident=n.node.ident, types=tys_);
    ret fld.fold_name(env, n.span, n_);
}

fn fold_ty[ENV](&ENV env, ast_fold[ENV] fld, @ty t) -> @ty {
    let ENV env_ = fld.update_env_for_ty(env, t);

    if (!fld.keep_going(env_)) {
        ret t;
    }

    alt (t.node) {
        case (ast.ty_nil) { ret fld.fold_ty_nil(env_, t.span); }
        case (ast.ty_bool) { ret fld.fold_ty_bool(env_, t.span); }
        case (ast.ty_int) { ret fld.fold_ty_int(env_, t.span); }
        case (ast.ty_uint) { ret fld.fold_ty_uint(env_, t.span); }

        case (ast.ty_machine(?m)) {
            ret fld.fold_ty_machine(env_, t.span, m);
        }

        case (ast.ty_char) { ret fld.fold_ty_char(env_, t.span); }
        case (ast.ty_str) { ret fld.fold_ty_str(env_, t.span); }

        case (ast.ty_box(?ty)) {
            auto ty_ = fold_ty(env, fld, ty);
            ret fld.fold_ty_box(env_, t.span, ty_);
        }

        case (ast.ty_vec(?ty)) {
            auto ty_ = fold_ty(env, fld, ty);
            ret fld.fold_ty_vec(env_, t.span, ty_);
        }

        case (ast.ty_tup(?elts)) {
            let vec[tup(bool, @ty)] elts_ = vec();
            for (tup(bool, @ty) elt in elts) {
                elts_ += tup(elt._0, fold_ty(env, fld, elt._1));
            }
            ret fld.fold_ty_tup(env_, t.span, elts);
        }

        case (ast.ty_path(?pth, ?ref_opt)) {
            let vec[ast.name] path = vec();
            for (ast.name n in pth) {
                path += fold_name(env, fld, n);
            }
            ret fld.fold_ty_path(env_, t.span, path, ref_opt);
        }
    }
}

fn fold_decl[ENV](&ENV env, ast_fold[ENV] fld, @decl d) -> @decl {
    let ENV env_ = fld.update_env_for_decl(env, d);

    if (!fld.keep_going(env_)) {
        ret d;
    }

    alt (d.node) {
        case (ast.decl_local(?id, ?ty_opt, ?expr_opt)) {
            auto ty_opt_ = none[@ast.ty];
            auto expr_opt_ = none[@ast.expr];
            alt (ty_opt) {
                case (some[@ast.ty](?t)) {
                    ty_opt_ = some[@ast.ty](fold_ty(env, fld, t));
                }
            }
            alt (expr_opt) {
                case (some[@ast.expr](?e)) {
                    expr_opt_ = some[@ast.expr](fold_expr(env, fld, e));
                }
            }
            ret fld.fold_decl_local(env_, d.span, id, ty_opt_, expr_opt_);
        }

        case (ast.decl_item(?id, ?item)) {
            auto item_ = fold_item(env_, fld, item);
            ret fld.fold_decl_item(env_, d.span, id, item_);
        }
    }

    fail;
}

fn fold_lval[ENV](&ENV env, ast_fold[ENV] fld, @lval lv) -> @lval {
    let ENV env_ = fld.update_env_for_lval(env, lv);

    if (!fld.keep_going(env_)) {
        ret lv;
    }

    alt (lv.node) {
        case (ast.lval_field(?e, ?i)) {
            auto ee = fold_expr(env_, fld, e);
            ret fld.fold_lval_field(env_, lv.span, ee, i);
        }

        case (ast.lval_index(?e, ?ix)) {
            auto ee = fold_expr(env_, fld, e);
            auto iix = fold_expr(env_, fld, ix);
            ret fld.fold_lval_index(env_, lv.span, ee, iix);
        }

        case (ast.lval_name(?n, ?r)) {
            auto n_ = fold_name(env_, fld, n);
            ret fld.fold_lval_name(env_, lv.span, n, r);
        }
    }

    fail;   // shoudn't be reached
}

// FIXME: Weird bug. Due to the way we auto-deref + in +=, we can't append a
// boxed value to a vector-of-boxes using +=.  Best to figure out a way to fix
// this. Deref-on-demand or something? It's a hazard of the ambiguity between
// single-element and vector append.
fn append[T](&vec[T] v, &T t) {
    v += t;
}

fn fold_exprs[ENV](&ENV env, ast_fold[ENV] fld, vec[@expr] es) -> vec[@expr] {
    let vec[@expr] exprs = vec();
    for (@expr e in es) {
        append[@expr](exprs, fold_expr(env, fld, e));
    }
    ret exprs;
}

fn fold_tup_entry[ENV](&ENV env, ast_fold[ENV] fld, &tup(bool,@expr) e)
    -> tup(bool,@expr) {
    ret tup(e._0, fold_expr(env, fld, e._1));
}

fn fold_rec_entry[ENV](&ENV env, ast_fold[ENV] fld, &tup(ident,@expr) e)
    -> tup(ident,@expr) {
    ret tup(e._0, fold_expr(env, fld, e._1));
}

fn fold_expr[ENV](&ENV env, ast_fold[ENV] fld, &@expr e) -> @expr {

    let ENV env_ = fld.update_env_for_expr(env, e);

    if (!fld.keep_going(env_)) {
        ret e;
    }

    alt (e.node) {
        case (ast.expr_vec(?es)) {
            auto ees = fold_exprs(env_, fld, es);
            ret fld.fold_expr_vec(env_, e.span, ees);
        }

        case (ast.expr_tup(?es)) {
            let vec[tup(bool,@expr)] entries = vec();
            for (tup(bool,@expr) entry in es) {
                entries += fold_tup_entry[ENV](env, fld, entry);
            }
            ret fld.fold_expr_tup(env_, e.span, entries);
        }

        case (ast.expr_rec(?es)) {
            let vec[tup(ident,@expr)] entries = vec();
            for (tup(ident,@expr) entry in es) {
                entries += fold_rec_entry(env, fld, entry);
            }
            ret fld.fold_expr_rec(env_, e.span, entries);
        }

        case (ast.expr_call(?f, ?args)) {
            auto ff = fold_expr(env_, fld, f);
            auto aargs = fold_exprs(env_, fld, args);
            ret fld.fold_expr_call(env_, e.span, ff, aargs);
        }

        case (ast.expr_binary(?op, ?a, ?b)) {
            auto aa = fold_expr(env_, fld, a);
            auto bb = fold_expr(env_, fld, b);
            ret fld.fold_expr_binary(env_, e.span, op, aa, bb);
        }

        case (ast.expr_unary(?op, ?a)) {
            auto aa = fold_expr(env_, fld, a);
            ret fld.fold_expr_unary(env_, e.span, op, a);
        }

        case (ast.expr_lit(?lit)) {
            ret fld.fold_expr_lit(env_, e.span, lit);
        }

        case (ast.expr_if(?cnd, ?thn, ?els)) {
            auto ccnd = fold_expr(env_, fld, cnd);
            auto tthn = fold_block(env_, fld, thn);
            auto eels = none[block];
            alt (els) {
                case (some[block](?b)) {
                    eels = some(fold_block(env_, fld, b));
                }
            }
            ret fld.fold_expr_if(env_, e.span, ccnd, tthn, eels);
        }

        case (ast.expr_block(?b)) {
            auto bb = fold_block(env_, fld, b);
            ret fld.fold_expr_block(env_, e.span, bb);
        }

        case (ast.expr_assign(?lhs, ?rhs)) {
            auto llhs = fold_lval(env_, fld, lhs);
            auto rrhs = fold_expr(env_, fld, rhs);
            ret fld.fold_expr_assign(env_, e.span, llhs, rrhs);
        }

        case (ast.expr_lval(?lv)) {
            auto llv = fold_lval(env_, fld, lv);
            ret fld.fold_expr_lval(env_, e.span, llv);
        }
    }

    ret e;
}


fn fold_stmt[ENV](&ENV env, ast_fold[ENV] fld, &@stmt s) -> @stmt {

    let ENV env_ = fld.update_env_for_stmt(env, s);

    if (!fld.keep_going(env_)) {
        ret s;
    }

    alt (s.node) {
        case (ast.stmt_decl(?d)) {
            auto dd = fold_decl(env_, fld, d);
            ret fld.fold_stmt_decl(env_, s.span, d);
        }

        case (ast.stmt_ret(?oe)) {
            auto oee = none[@expr];
            alt (oe) {
                case (some[@expr](?e)) {
                    oee = some(fold_expr(env_, fld, e));
                }
            }
            ret fld.fold_stmt_ret(env_, s.span, oee);
        }

        case (ast.stmt_log(?e)) {
            auto ee = fold_expr(env_, fld, e);
            ret fld.fold_stmt_log(env_, s.span, e);
        }

        case (ast.stmt_expr(?e)) {
            auto ee = fold_expr(env_, fld, e);
            ret fld.fold_stmt_expr(env_, s.span, e);
        }
    }
    ret s;
}

fn fold_block[ENV](&ENV env, ast_fold[ENV] fld, &block blk) -> block {
    let vec[@ast.stmt] stmts = vec();
    for (@ast.stmt s in blk.node) {
        append[@ast.stmt](stmts, fold_stmt[ENV](env, fld, s));
    }
    ret respan(blk.span, stmts);
}

fn fold_slot[ENV](&ENV env, ast_fold[ENV] fld, &slot s) -> slot {
    auto ty = fold_ty(env, fld, s.ty);
    ret rec(ty=ty, mode=s.mode, id=s.id);
}


fn fold_fn[ENV](&ENV env, ast_fold[ENV] fld, &ast._fn f) -> ast._fn {

    let vec[ast.input] inputs = vec();
    for (ast.input i in f.inputs) {
        inputs += rec(slot=fold_slot(env, fld, i.slot),
                      ident=i.ident);
    }
    auto output = fold_ty[ENV](env, fld, @f.output);
    auto body = fold_block[ENV](env, fld, f.body);

    ret fld.fold_fn(env, inputs, *output, body);
}

fn fold_item[ENV](&ENV env, ast_fold[ENV] fld, @item i) -> @item {

    let ENV env_ = fld.update_env_for_item(env, i);

    if (!fld.keep_going(env_)) {
        ret i;
    }

    alt (i.node) {

        case (ast.item_fn(?ff, ?id)) {
            let ast._fn ff_ = fold_fn[ENV](env_, fld, ff);
            ret fld.fold_item_fn(env_, i.span, ff_, id);
        }

        case (ast.item_mod(?mm)) {
            let ast._mod mm_ = fold_mod[ENV](env_, fld, mm);
            ret fld.fold_item_mod(env_, i.span, mm_);
        }

        case (ast.item_ty(?ty, ?id)) {
            let @ast.ty ty_ = fold_ty[ENV](env_, fld, ty);
            ret fld.fold_item_ty(env_, i.span, ty_, id);
        }
    }

    fail;
}


fn fold_mod[ENV](&ENV e, ast_fold[ENV] fld, &ast._mod m_in) -> ast._mod {

    auto m_out = new_str_hash[@item]();

    for each (tup(ident, @item) pairs in m_in.items()) {
        auto i = fold_item[ENV](e, fld, pairs._1);
        m_out.insert(pairs._0, i);
    }

    ret fld.fold_mod(e, m_out);
 }

fn fold_crate[ENV](&ENV env, ast_fold[ENV] fld, @ast.crate c) -> @ast.crate {
    let ENV env_ = fld.update_env_for_crate(env, c);
    let ast._mod m = fold_mod[ENV](env_, fld, c.node.module);
    ret fld.fold_crate(env_, c.span, m);
}

//// Identity folds.

fn respan[T](&span sp, &T t) -> spanned[T] {
    ret rec(node=t, span=sp);
}


// Name identity.

fn identity_fold_name[ENV](&ENV env, &span sp, ast.name_ n) -> name {
    ret respan(sp, n);
}

// Type identities.

fn identity_fold_ty_nil[ENV](&ENV env, &span sp) -> @ty {
    ret @respan(sp, ast.ty_nil);
}

fn identity_fold_ty_bool[ENV](&ENV env, &span sp) -> @ty {
    ret @respan(sp, ast.ty_bool);
}

fn identity_fold_ty_int[ENV](&ENV env, &span sp) -> @ty {
    ret @respan(sp, ast.ty_int);
}

fn identity_fold_ty_uint[ENV](&ENV env, &span sp) -> @ty {
    ret @respan(sp, ast.ty_uint);
}

fn identity_fold_ty_machine[ENV](&ENV env, &span sp,
                                 ty_mach tm) -> @ty {
    ret @respan(sp, ast.ty_machine(tm));
}

fn identity_fold_ty_char[ENV](&ENV env, &span sp) -> @ty {
    ret @respan(sp, ast.ty_char);
}

fn identity_fold_ty_str[ENV](&ENV env, &span sp) -> @ty {
    ret @respan(sp, ast.ty_str);
}

fn identity_fold_ty_box[ENV](&ENV env, &span sp, @ty t) -> @ty {
    ret @respan(sp, ast.ty_box(t));
}

fn identity_fold_ty_vec[ENV](&ENV env, &span sp, @ty t) -> @ty {
    ret @respan(sp, ast.ty_vec(t));
}

fn identity_fold_ty_tup[ENV](&ENV env, &span sp, vec[tup(bool,@ty)] elts)
    -> @ty {
    ret @respan(sp, ast.ty_tup(elts));
}

fn identity_fold_ty_path[ENV](&ENV env, &span sp, ast.path p,
                        &option[referent] r) -> @ty {
    ret @respan(sp, ast.ty_path(p, r));
}


// Expr identities.

fn identity_fold_expr_vec[ENV](&ENV env, &span sp, vec[@expr] es) -> @expr {
    ret @respan(sp, ast.expr_vec(es));
}

fn identity_fold_expr_tup[ENV](&ENV env, &span sp, vec[tup(bool, @expr)] es)
        -> @expr {
    ret @respan(sp, ast.expr_tup(es));
}

fn identity_fold_expr_rec[ENV](&ENV env, &span sp,
                               vec[tup(ident,@expr)] fields)
    -> @expr {
    ret @respan(sp, ast.expr_rec(fields));
}

fn identity_fold_expr_call[ENV](&ENV env, &span sp, @expr f,
                                vec[@expr] args) -> @expr {
    ret @respan(sp, ast.expr_call(f, args));
}

fn identity_fold_expr_binary[ENV](&ENV env, &span sp, ast.binop b,
                                  @expr lhs, @expr rhs) -> @expr {
    ret @respan(sp, ast.expr_binary(b, lhs, rhs));
}

fn identity_fold_expr_unary[ENV](&ENV env, &span sp,
                                 ast.unop u, @expr e) -> @expr {
    ret @respan(sp, ast.expr_unary(u, e));
}

fn identity_fold_expr_lit[ENV](&ENV env, &span sp, @ast.lit lit) -> @expr {
    ret @respan(sp, ast.expr_lit(lit));
}

fn identity_fold_expr_if[ENV](&ENV env, &span sp,
                              @expr cond, block thn,
                              &option[block] els) -> @expr {
    ret @respan(sp, ast.expr_if(cond, thn, els));
}

fn identity_fold_expr_block[ENV](&ENV env, &span sp, block blk) -> @expr {
    ret @respan(sp, ast.expr_block(blk));
}

fn identity_fold_expr_assign[ENV](&ENV env, &span sp,
                                  @lval lhs, @expr rhs) -> @expr {
    ret @respan(sp, ast.expr_assign(lhs, rhs));
}

fn identity_fold_expr_lval[ENV](&ENV env, &span sp, @lval lv) -> @expr {
    ret @respan(sp, ast.expr_lval(lv));
}


// Lvalue identities.

fn identity_fold_lval_field[ENV](&ENV env, &span sp,
                                 @expr e, ident i) -> @lval {
    ret @respan(sp, ast.lval_field(e, i));
}

fn identity_fold_lval_index[ENV](&ENV env, &span sp,
                                 @expr e, @expr ix) -> @lval {
    ret @respan(sp, ast.lval_index(e, ix));
}

fn identity_fold_lval_name[ENV](&ENV env, &span sp,
                                &name n, &option[referent] r) -> @lval {
    ret @respan(sp, ast.lval_name(n, r));
}


// Decl identities.

fn identity_fold_decl_local[ENV](&ENV e, &span sp,
                                 ident i, &option[@ty] t,
                                 &option[@expr] init) -> @decl {
    ret @respan(sp, ast.decl_local(i, t, init));
}

fn identity_fold_decl_item[ENV](&ENV e, &span sp,
                                ident id, @item i) -> @decl {
    ret @respan(sp, ast.decl_item(id, i));
}


// Stmt identities.

fn identity_fold_stmt_decl[ENV](&ENV env, &span sp, @decl d) -> @stmt {
    ret @respan(sp, ast.stmt_decl(d));
}

fn identity_fold_stmt_ret[ENV](&ENV env, &span sp,
                               &option[@expr] rv) -> @stmt {
    ret @respan(sp, ast.stmt_ret(rv));
}

fn identity_fold_stmt_log[ENV](&ENV e, &span sp, @expr x) -> @stmt {
    ret @respan(sp, ast.stmt_log(x));
}

fn identity_fold_stmt_expr[ENV](&ENV e, &span sp, @expr x) -> @stmt {
    ret @respan(sp, ast.stmt_expr(x));
}


// Item identities.

fn identity_fold_item_fn[ENV](&ENV e, &span sp, &ast._fn f,
                              ast.item_id id) -> @item {
    ret @respan(sp, ast.item_fn(f, id));
}

fn identity_fold_item_mod[ENV](&ENV e, &span sp, &ast._mod m) -> @item {
    ret @respan(sp, ast.item_mod(m));
}

fn identity_fold_item_ty[ENV](&ENV e, &span sp, @ty t,
                              ast.item_id id) -> @item {
    ret @respan(sp, ast.item_ty(t, id));
}


// Additional identities.

fn identity_fold_block[ENV](&ENV e, &span sp, vec[@stmt] stmts) -> block {
    ret respan(sp, stmts);
}

fn identity_fold_fn[ENV](&ENV e,
                         vec[ast.input] inputs,
                         &ast.ty output,
                         block body) -> ast._fn {
    ret rec(inputs=inputs, output=output, body=body);
}

fn identity_fold_mod[ENV](&ENV e, &ast._mod m) -> ast._mod {
    ret m;
}

fn identity_fold_crate[ENV](&ENV e, &span sp, &ast._mod m) -> @ast.crate {
    ret @respan(sp, rec(module=m));
}


// Env update identities.

fn identity_update_env_for_crate[ENV](&ENV e, @ast.crate c) -> ENV {
    ret e;
}

fn identity_update_env_for_item[ENV](&ENV e, @item i) -> ENV {
    ret e;
}

fn identity_update_env_for_stmt[ENV](&ENV e, @stmt s) -> ENV {
    ret e;
}

fn identity_update_env_for_decl[ENV](&ENV e, @decl d) -> ENV {
    ret e;
}

fn identity_update_env_for_lval[ENV](&ENV e, @lval l) -> ENV {
    ret e;
}

fn identity_update_env_for_expr[ENV](&ENV e, @expr x) -> ENV {
    ret e;
}

fn identity_update_env_for_ty[ENV](&ENV e, @ty t) -> ENV {
    ret e;
}


// Always-true traversal control fn.

fn always_keep_going[ENV](&ENV e) -> bool {
    ret true;
}


fn new_identity_fold[ENV]() -> ast_fold[ENV] {
    ret @rec
        (
         fold_name       = bind identity_fold_name[ENV](_,_,_),

         fold_ty_nil     = bind identity_fold_ty_nil[ENV](_,_),
         fold_ty_bool    = bind identity_fold_ty_bool[ENV](_,_),
         fold_ty_int     = bind identity_fold_ty_int[ENV](_,_),
         fold_ty_uint    = bind identity_fold_ty_uint[ENV](_,_),
         fold_ty_machine = bind identity_fold_ty_machine[ENV](_,_,_),
         fold_ty_char    = bind identity_fold_ty_char[ENV](_,_),
         fold_ty_str     = bind identity_fold_ty_str[ENV](_,_),
         fold_ty_box     = bind identity_fold_ty_box[ENV](_,_,_),
         fold_ty_vec     = bind identity_fold_ty_vec[ENV](_,_,_),
         fold_ty_tup     = bind identity_fold_ty_tup[ENV](_,_,_),
         fold_ty_path    = bind identity_fold_ty_path[ENV](_,_,_,_),

         fold_expr_vec    = bind identity_fold_expr_vec[ENV](_,_,_),
         fold_expr_tup    = bind identity_fold_expr_tup[ENV](_,_,_),
         fold_expr_rec    = bind identity_fold_expr_rec[ENV](_,_,_),
         fold_expr_call   = bind identity_fold_expr_call[ENV](_,_,_,_),
         fold_expr_binary = bind identity_fold_expr_binary[ENV](_,_,_,_,_),
         fold_expr_unary  = bind identity_fold_expr_unary[ENV](_,_,_,_),
         fold_expr_lit    = bind identity_fold_expr_lit[ENV](_,_,_),
         fold_expr_if     = bind identity_fold_expr_if[ENV](_,_,_,_,_),
         fold_expr_block  = bind identity_fold_expr_block[ENV](_,_,_),
         fold_expr_assign = bind identity_fold_expr_assign[ENV](_,_,_,_),
         fold_expr_lval   = bind identity_fold_expr_lval[ENV](_,_,_),

         fold_lval_field  = bind identity_fold_lval_field[ENV](_,_,_,_),
         fold_lval_index  = bind identity_fold_lval_index[ENV](_,_,_,_),
         fold_lval_name   = bind identity_fold_lval_name[ENV](_,_,_,_),

         fold_decl_local  = bind identity_fold_decl_local[ENV](_,_,_,_,_),
         fold_decl_item   = bind identity_fold_decl_item[ENV](_,_,_,_),

         fold_stmt_decl   = bind identity_fold_stmt_decl[ENV](_,_,_),
         fold_stmt_ret    = bind identity_fold_stmt_ret[ENV](_,_,_),
         fold_stmt_log    = bind identity_fold_stmt_log[ENV](_,_,_),
         fold_stmt_expr   = bind identity_fold_stmt_expr[ENV](_,_,_),

         fold_item_fn   = bind identity_fold_item_fn[ENV](_,_,_,_),
         fold_item_mod  = bind identity_fold_item_mod[ENV](_,_,_),
         fold_item_ty   = bind identity_fold_item_ty[ENV](_,_,_,_),

         fold_block = bind identity_fold_block[ENV](_,_,_),
         fold_fn = bind identity_fold_fn[ENV](_,_,_,_),
         fold_mod = bind identity_fold_mod[ENV](_,_),
         fold_crate = bind identity_fold_crate[ENV](_,_,_),

         update_env_for_crate = bind identity_update_env_for_crate[ENV](_,_),
         update_env_for_item = bind identity_update_env_for_item[ENV](_,_),
         update_env_for_stmt = bind identity_update_env_for_stmt[ENV](_,_),
         update_env_for_decl = bind identity_update_env_for_decl[ENV](_,_),
         update_env_for_lval = bind identity_update_env_for_lval[ENV](_,_),
         update_env_for_expr = bind identity_update_env_for_expr[ENV](_,_),
         update_env_for_ty = bind identity_update_env_for_ty[ENV](_,_),

         keep_going = bind always_keep_going[ENV](_)
         );
}


//
// Local Variables:
// mode: rust
// fill-column: 78;
// indent-tabs-mode: nil
// c-basic-offset: 4
// buffer-file-coding-system: utf-8-unix
// compile-command: "make -k -C ../.. 2>&1 | sed -e 's/\\/x\\//x:\\//g'";
// End:
//