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diff --git a/src/expr-visitor.h b/src/expr-visitor.h
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+/*
+ * Copyright 2017 WebAssembly Community Group participants
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef WABT_EXPR_VISITOR_H_
+#define WABT_EXPR_VISITOR_H_
+
+#include "common.h"
+
+namespace wabt {
+
+struct Expr;
+struct Func;
+
+class ExprVisitor {
+ public:
+  class Delegate;
+  class DelegateNop;
+
+  explicit ExprVisitor(Delegate* delegate);
+
+  Result VisitExpr(Expr*);
+  Result VisitExprList(Expr*);
+  Result VisitFunc(Func*);
+
+ private:
+  Delegate* delegate_;
+};
+
+class ExprVisitor::Delegate {
+ public:
+  virtual ~Delegate() {}
+
+  virtual Result OnBinaryExpr(Expr*) = 0;
+  virtual Result BeginBlockExpr(Expr*) = 0;
+  virtual Result EndBlockExpr(Expr*) = 0;
+  virtual Result OnBrExpr(Expr*) = 0;
+  virtual Result OnBrIfExpr(Expr*) = 0;
+  virtual Result OnBrTableExpr(Expr*) = 0;
+  virtual Result OnCallExpr(Expr*) = 0;
+  virtual Result OnCallIndirectExpr(Expr*) = 0;
+  virtual Result OnCompareExpr(Expr*) = 0;
+  virtual Result OnConstExpr(Expr*) = 0;
+  virtual Result OnConvertExpr(Expr*) = 0;
+  virtual Result OnCurrentMemoryExpr(Expr*) = 0;
+  virtual Result OnDropExpr(Expr*) = 0;
+  virtual Result OnGetGlobalExpr(Expr*) = 0;
+  virtual Result OnGetLocalExpr(Expr*) = 0;
+  virtual Result OnGrowMemoryExpr(Expr*) = 0;
+  virtual Result BeginIfExpr(Expr*) = 0;
+  virtual Result AfterIfTrueExpr(Expr*) = 0;
+  virtual Result EndIfExpr(Expr*) = 0;
+  virtual Result OnLoadExpr(Expr*) = 0;
+  virtual Result BeginLoopExpr(Expr*) = 0;
+  virtual Result EndLoopExpr(Expr*) = 0;
+  virtual Result OnNopExpr(Expr*) = 0;
+  virtual Result OnReturnExpr(Expr*) = 0;
+  virtual Result OnSelectExpr(Expr*) = 0;
+  virtual Result OnSetGlobalExpr(Expr*) = 0;
+  virtual Result OnSetLocalExpr(Expr*) = 0;
+  virtual Result OnStoreExpr(Expr*) = 0;
+  virtual Result OnTeeLocalExpr(Expr*) = 0;
+  virtual Result OnUnaryExpr(Expr*) = 0;
+  virtual Result OnUnreachableExpr(Expr*) = 0;
+};
+
+class ExprVisitor::DelegateNop : public ExprVisitor::Delegate {
+ public:
+  Result OnBinaryExpr(Expr*) override { return Result::Ok; }
+  Result BeginBlockExpr(Expr*) override { return Result::Ok; }
+  Result EndBlockExpr(Expr*) override { return Result::Ok; }
+  Result OnBrExpr(Expr*) override { return Result::Ok; }
+  Result OnBrIfExpr(Expr*) override { return Result::Ok; }
+  Result OnBrTableExpr(Expr*) override { return Result::Ok; }
+  Result OnCallExpr(Expr*) override { return Result::Ok; }
+  Result OnCallIndirectExpr(Expr*) override { return Result::Ok; }
+  Result OnCompareExpr(Expr*) override { return Result::Ok; }
+  Result OnConstExpr(Expr*) override { return Result::Ok; }
+  Result OnConvertExpr(Expr*) override { return Result::Ok; }
+  Result OnCurrentMemoryExpr(Expr*) override { return Result::Ok; }
+  Result OnDropExpr(Expr*) override { return Result::Ok; }
+  Result OnGetGlobalExpr(Expr*) override { return Result::Ok; }
+  Result OnGetLocalExpr(Expr*) override { return Result::Ok; }
+  Result OnGrowMemoryExpr(Expr*) override { return Result::Ok; }
+  Result BeginIfExpr(Expr*) override { return Result::Ok; }
+  Result AfterIfTrueExpr(Expr*) override { return Result::Ok; }
+  Result EndIfExpr(Expr*) override { return Result::Ok; }
+  Result OnLoadExpr(Expr*) override { return Result::Ok; }
+  Result BeginLoopExpr(Expr*) override { return Result::Ok; }
+  Result EndLoopExpr(Expr*) override { return Result::Ok; }
+  Result OnNopExpr(Expr*) override { return Result::Ok; }
+  Result OnReturnExpr(Expr*) override { return Result::Ok; }
+  Result OnSelectExpr(Expr*) override { return Result::Ok; }
+  Result OnSetGlobalExpr(Expr*) override { return Result::Ok; }
+  Result OnSetLocalExpr(Expr*) override { return Result::Ok; }
+  Result OnStoreExpr(Expr*) override { return Result::Ok; }
+  Result OnTeeLocalExpr(Expr*) override { return Result::Ok; }
+  Result OnUnaryExpr(Expr*) override { return Result::Ok; }
+  Result OnUnreachableExpr(Expr*) override { return Result::Ok; }
+};
+
+}  // namespace wabt
+
+#endif  // WABT_EXPR_VISITOR_H_