Added implementation of immutable (functional) maps and sets, as

implemented on top of a functional AVL tree.  The AVL balancing code
is inspired by the OCaml implementation of Map, which also uses a functional
AVL tree.

Documentation is currently limited and cleanups are planned, but this code
compiles and has been tested.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@42813 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/ImmutableMap.h

@@ -0,0 +1,163 @@
+//===--- ImmutableMap.h - Immutable (functional) map interface --*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by Ted Kremenek and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the ImmutableMap class.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_IMMAP_H
+#define LLVM_ADT_IMMAP_H
+
+#include "llvm/ADT/ImmutableSet.h"
+
+namespace llvm {
+
+/// ImutKeyValueInfo -Traits class used by ImmutableMap.  While both the first and
+/// second elements in a pair are used to generate profile information,
+/// only the first element (the key) is used by isEqual and isLess.
+template <typename T, typename S>
+struct ImutKeyValueInfo {
+  typedef const std::pair<T,S> value_type;
+  typedef const value_type& value_type_ref;
+  typedef const T   key_type;
+  typedef const T&  key_type_ref;
+  typedef const S   data_type;
+  typedef const S&  data_type_ref;
+  
+  static inline key_type_ref KeyOfValue(value_type_ref V) {
+    return V.first;
+  }
+  
+  static inline bool isEqual(key_type_ref L, key_type_ref R) {
+    return ImutContainerInfo<T>::isEqual(L,R);
+  }
+  
+  static inline bool isLess(key_type_ref L, key_type_ref R) {
+    return ImutContainerInfo<T>::isLess(L,R);
+  }
+  
+  static inline void Profile(FoldingSetNodeID& ID, value_type_ref V) {
+    ImutContainerInfo<T>::Profile(ID, V.first);
+    ImutContainerInfo<S>::Profile(ID, V.second);
+  }
+};  
+
+  
+template <typename KeyT, typename ValT, 
+          typename ValInfo = ImutKeyValueInfo<KeyT,ValT> >
+class ImmutableMap {
+  typedef typename ValInfo::value_type      value_type;
+  typedef typename ValInfo::value_type_ref  value_type_ref;
+  typedef typename ValInfo::key_type        key_type;
+  typedef typename ValInfo::key_type_ref    key_type_ref;
+  typedef typename ValInfo::data_type       data_type;
+  typedef typename ValInfo::data_type_ref   data_type_ref;
+  
+private:  
+  typedef ImutAVLTree<ValInfo> TreeTy;
+  TreeTy* Root;
+  
+  ImmutableMap(TreeTy* R) : Root(R) {}
+  
+public:
+  
+  class Factory {
+    typename TreeTy::Factory F;
+    
+  public:
+    Factory() {}
+    
+    ImmutableMap GetEmptyMap() { return ImmutableMap(F.GetEmptyTree()); }
+    
+    ImmutableMap Add(ImmutableMap Old, key_type_ref K, data_type_ref D) {
+      return ImmutableMap(F.Add(Old.Root,std::make_pair<key_type,data_type>(K,D)));
+    }
+    
+    ImmutableMap Remove(ImmutableMap Old, key_type_ref K) {
+      return ImmutableMap(F.Remove(Old.Root,K));
+    }        
+    
+  private:
+    Factory(const Factory& RHS) {};
+    void operator=(const Factory& RHS) {};    
+  };
+  
+  friend class Factory;  
+  
+  bool contains(key_type_ref K) const {
+    return Root ? Root->contains(K) : false;
+  }
+  
+  data_type* find(key_type_ref K) const {
+    if (Root) {
+      TreeTy* T = Root->find(K);
+      if (T) return &T->getValue().second;
+    }
+    
+    return NULL;
+  }
+  
+  bool operator==(ImmutableMap RHS) const {
+    return Root && RHS.Root ? Root->isEqual(*RHS.Root) : Root == RHS.Root;
+  }
+  
+  bool operator!=(ImmutableMap RHS) const {
+    return Root && RHS.Root ? Root->isNotEqual(*RHS.Root) : Root != RHS.Root;
+  }
+  
+  bool isEmpty() const { return !Root; }
+
+  //===--------------------------------------------------===//    
+  // Foreach - A limited form of map iteration.
+  //===--------------------------------------------------===//
+
+private:
+  template <typename Callback>
+  struct CBWrapper {
+    Callback C;
+    void operator()(value_type_ref V) { C(V.first,V.second); }    
+  };  
+  
+  template <typename Callback>
+  struct CBWrapperRef {
+    Callback &C;
+    CBWrapperRef(Callback& c) : C(c) {}
+    
+    void operator()(value_type_ref V) { C(V.first,V.second); }    
+  };
+  
+public:  
+  template <typename Callback>
+  void foreach(Callback& C) { 
+    if (Root) { 
+      CBWrapperRef<Callback> CB(C);
+      Root->foreach(CB);
+    }
+  }
+  
+  template <typename Callback>
+  void foreach() { 
+    if (Root) {
+      CBWrapper<Callback> CB;
+      Root->foreach(CB);
+    }
+  }
+  
+  //===--------------------------------------------------===//    
+  // For testing.
+  //===--------------------------------------------------===//  
+  
+  void verify() const { if (Root) Root->verify(); }
+  unsigned getHeight() const { return Root ? Root->getHeight() : 0; }
+  
+};
+  
+} // end namespace llvm
+
+#endif

include/llvm/ADT/ImmutableSet.h

@@ -0,0 +1,608 @@
+//===--- ImmutableSet.h - Immutable (functional) set interface --*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by Ted Kremenek and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the ImutAVLTree and ImmutableSet classes.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_IMSET_H
+#define LLVM_ADT_IMSET_H
+
+#include "llvm/Support/Allocator.h"
+#include "llvm/ADT/FoldingSet.h"
+#include <cassert>
+
+namespace llvm {
+  
+//===----------------------------------------------------------------------===//    
+// Immutable AVL-Tree Definition.
+//===----------------------------------------------------------------------===//
+
+template <typename ImutInfo> class ImutAVLFactory;
+
+template <typename ImutInfo >
+class ImutAVLTree : public FoldingSetNode {
+  struct ComputeIsEqual;
+public:
+  typedef typename ImutInfo::key_type_ref   key_type_ref;
+  typedef typename ImutInfo::value_type     value_type;
+  typedef typename ImutInfo::value_type_ref value_type_ref;
+  typedef ImutAVLFactory<ImutInfo>          Factory;
+  friend class ImutAVLFactory<ImutInfo>;
+  
+  //===----------------------------------------------------===//  
+  // Public Interface.
+  //===----------------------------------------------------===//  
+  
+  ImutAVLTree* getLeft() const { return reinterpret_cast<ImutAVLTree*>(Left); }  
+  
+  ImutAVLTree* getRight() const { return Right; }  
+  
+  unsigned getHeight() const { return Height; }  
+  
+  const value_type& getValue() const { return Value; }
+  
+  ImutAVLTree* find(key_type_ref K) {
+    ImutAVLTree *T = this;
+    
+    while (T) {
+      key_type_ref CurrentKey = ImutInfo::KeyOfValue(Value(T));
+      
+      if (ImutInfo::isEqual(K,CurrentKey))
+        return T;
+      else if (ImutInfo::isLess(K,CurrentKey))
+        T = T->getLeft();
+      else
+        T = T->getRight();
+    }
+    
+    return NULL;
+  }
+  
+  unsigned size() const {
+    unsigned n = 1;
+    
+    if (const ImutAVLTree* L = getLeft())  n += L->size();
+    if (const ImutAVLTree* R = getRight()) n += R->size();
+    
+    return n;
+  }
+  
+  
+  
+  bool isEqual(const ImutAVLTree& RHS) const {
+    // FIXME: Todo.
+    return true;    
+  }
+  
+  bool isNotEqual(const ImutAVLTree& RHS) const { return !isEqual(RHS); }
+  
+  bool contains(const key_type_ref K) { return (bool) find(K); }
+  
+  template <typename Callback>
+  void foreach(Callback& C) {
+    if (ImutAVLTree* L = getLeft()) L->foreach(C);
+    
+    C(Value);    
+    
+    if (ImutAVLTree* R = getRight()) R->foreach(C);
+  }
+  
+  unsigned verify() const {
+    unsigned HL = getLeft() ? getLeft()->verify() : 0;
+    unsigned HR = getRight() ? getRight()->verify() : 0;
+    
+    assert (getHeight() == ( HL > HR ? HL : HR ) + 1 
+            && "Height calculation wrong.");
+    
+    assert ((HL > HR ? HL-HR : HR-HL) <= 2
+            && "Balancing invariant violated.");
+    
+    
+    assert (!getLeft()
+            || ImutInfo::isLess(ImutInfo::KeyOfValue(getLeft()->getValue()),
+                                ImutInfo::KeyOfValue(getValue()))
+            && "Value in left child is not less that current value.");
+    
+    
+    assert (!getRight()
+            || ImutInfo::isLess(ImutInfo::KeyOfValue(getValue()),
+                                ImutInfo::KeyOfValue(getRight()->getValue()))
+            && "Current value is not less that value of right child.");
+    
+    return getHeight();
+  }  
+  
+  //===----------------------------------------------------===//  
+  // Internal Values.
+  //===----------------------------------------------------===//
+  
+private:
+  uintptr_t        Left;
+  ImutAVLTree*     Right;
+  unsigned         Height;
+  value_type       Value;
+  
+  //===----------------------------------------------------===//  
+  // Profiling or FoldingSet.
+  //===----------------------------------------------------===//
+  
+  static inline
+  void Profile(FoldingSetNodeID& ID, ImutAVLTree* L, ImutAVLTree* R,
+               unsigned H, value_type_ref V) {    
+    ID.AddPointer(L);
+    ID.AddPointer(R);
+    ID.AddInteger(H);
+    ImutInfo::Profile(ID,V);
+  }
+  
+public:
+  
+  void Profile(FoldingSetNodeID& ID) {
+    Profile(ID,getSafeLeft(),getRight(),getHeight(),getValue());    
+  }
+  
+  //===----------------------------------------------------===//    
+  // Internal methods (node manipulation; used by Factory).
+  //===----------------------------------------------------===//
+  
+private:
+  
+  ImutAVLTree(ImutAVLTree* l, ImutAVLTree* r, value_type_ref v, unsigned height)
+  : Left(reinterpret_cast<uintptr_t>(l) | 0x1),
+  Right(r), Height(height), Value(v) {}
+  
+  bool isMutable() const { return Left & 0x1; }
+  
+  ImutAVLTree* getSafeLeft() const { 
+    return reinterpret_cast<ImutAVLTree*>(Left & ~0x1);
+  }
+  
+  // Mutating operations.  A tree root can be manipulated as long as
+  // its reference has not "escaped" from internal methods of a
+  // factory object (see below).  When a tree pointer is externally
+  // viewable by client code, the internal "mutable bit" is cleared
+  // to mark the tree immutable.  Note that a tree that still has
+  // its mutable bit set may have children (subtrees) that are themselves
+  // immutable.
+  
+  void RemoveMutableFlag() {
+    assert (Left & 0x1 && "Mutable flag already removed.");
+    Left &= ~0x1;
+  }
+  
+  void setLeft(ImutAVLTree* NewLeft) {
+    assert (isMutable());
+    Left = reinterpret_cast<uintptr_t>(NewLeft) | 0x1;
+  }
+  
+  void setRight(ImutAVLTree* NewRight) {
+    assert (isMutable());
+    Right = NewRight;
+  }
+  
+  void setHeight(unsigned h) {
+    assert (isMutable());
+    Height = h;
+  }
+};
+
+//===----------------------------------------------------------------------===//    
+// Immutable AVL-Tree Factory class.
+//===----------------------------------------------------------------------===//
+
+template <typename ImutInfo >  
+class ImutAVLFactory {
+  typedef ImutAVLTree<ImutInfo> TreeTy;
+  typedef typename TreeTy::value_type_ref value_type_ref;
+  typedef typename TreeTy::key_type_ref   key_type_ref;
+  
+  typedef FoldingSet<TreeTy> CacheTy;
+  
+  CacheTy Cache;  
+  BumpPtrAllocator Allocator;    
+  
+  //===--------------------------------------------------===//    
+  // Public interface.
+  //===--------------------------------------------------===//
+  
+public:
+  ImutAVLFactory() {}
+  
+  TreeTy* Add(TreeTy* T, value_type_ref V) {
+    T = Add_internal(V,T);
+    MarkImmutable(T);
+    return T;
+  }
+  
+  TreeTy* Remove(TreeTy* T, key_type_ref V) {
+    T = Remove_internal(V,T);
+    MarkImmutable(T);
+    return T;
+  }
+  
+  TreeTy* GetEmptyTree() const { return NULL; }
+  
+  //===--------------------------------------------------===//    
+  // A bunch of quick helper functions used for reasoning
+  // about the properties of trees and their children.
+  // These have succinct names so that the balancing code
+  // is as terse (and readable) as possible.
+  //===--------------------------------------------------===//
+private:
+  
+  bool isEmpty(TreeTy* T) const {
+    return !T;
+  }
+  
+  unsigned Height(TreeTy* T) const {
+    return T ? T->getHeight() : 0;
+  }
+  
+  TreeTy* Left(TreeTy* T) const {
+    assert (T);
+    return T->getSafeLeft();
+  }
+  
+  TreeTy* Right(TreeTy* T) const {
+    assert (T);
+    return T->getRight();
+  }
+  
+  value_type_ref Value(TreeTy* T) const {
+    assert (T);
+    return T->Value;
+  }
+  
+  unsigned IncrementHeight(TreeTy* L, TreeTy* R) const {
+    unsigned hl = Height(L);
+    unsigned hr = Height(R);
+    return ( hl > hr ? hl : hr ) + 1;
+  }
+  
+  //===--------------------------------------------------===//    
+  // "Create" is used to generate new tree roots that link
+  // to other trees.  The functon may also simply move links
+  // in an existing root if that root is still marked mutable.
+  // This is necessary because otherwise our balancing code
+  // would leak memory as it would create nodes that are
+  // then discarded later before the finished tree is
+  // returned to the caller.
+  //===--------------------------------------------------===//
+  
+  TreeTy* Create(TreeTy* L, value_type_ref V, TreeTy* R) {
+    FoldingSetNodeID ID;      
+    unsigned height = IncrementHeight(L,R);
+    
+    TreeTy::Profile(ID,L,R,height,V);      
+    void* InsertPos;
+    
+    if (TreeTy* T = Cache.FindNodeOrInsertPos(ID,InsertPos))
+      return T;
+    
+    assert (InsertPos != NULL);
+    
+    // FIXME: more intelligent calculation of alignment.
+    TreeTy* T = (TreeTy*) Allocator.Allocate(sizeof(*T),16);
+    new (T) TreeTy(L,R,V,height);
+    
+    Cache.InsertNode(T,InsertPos);
+    return T;      
+  }
+  
+  TreeTy* Create(TreeTy* L, TreeTy* OldTree, TreeTy* R) {      
+    assert (!isEmpty(OldTree));
+    
+    if (OldTree->isMutable()) {
+      OldTree->setLeft(L);
+      OldTree->setRight(R);
+      OldTree->setHeight(IncrementHeight(L,R));
+      return OldTree;
+    }
+    else return Create(L, Value(OldTree), R);
+  }
+  
+  /// Balance - Used by Add_internal and Remove_internal to
+  ///  balance a newly created tree.
+  TreeTy* Balance(TreeTy* L, value_type_ref V, TreeTy* R) {
+    
+    unsigned hl = Height(L);
+    unsigned hr = Height(R);
+    
+    if (hl > hr + 2) {
+      assert (!isEmpty(L) &&
+              "Left tree cannot be empty to have a height >= 2.");
+      
+      TreeTy* LL = Left(L);
+      TreeTy* LR = Right(L);
+      
+      if (Height(LL) >= Height(LR))
+        return Create(LL, L, Create(LR,V,R));
+      
+      assert (!isEmpty(LR) &&
+              "LR cannot be empty because it has a height >= 1.");
+      
+      TreeTy* LRL = Left(LR);
+      TreeTy* LRR = Right(LR);
+      
+      return Create(Create(LL,L,LRL), LR, Create(LRR,V,R));                              
+    }
+    else if (hr > hl + 2) {
+      assert (!isEmpty(R) &&
+              "Right tree cannot be empty to have a height >= 2.");
+      
+      TreeTy* RL = Left(R);
+      TreeTy* RR = Right(R);
+      
+      if (Height(RR) >= Height(RL))
+        return Create(Create(L,V,RL), R, RR);
+      
+      assert (!isEmpty(RL) &&
+              "RL cannot be empty because it has a height >= 1.");
+      
+      TreeTy* RLL = Left(RL);
+      TreeTy* RLR = Right(RL);
+      
+      return Create(Create(L,V,RLL), RL, Create(RLR,R,RR));
+    }
+    else
+      return Create(L,V,R);
+  }
+  
+  /// Add_internal - Creates a new tree that includes the specified
+  ///  data and the data from the original tree.  If the original tree
+  ///  already contained the data item, the original tree is returned.
+  TreeTy* Add_internal(value_type_ref V, TreeTy* T) {
+    if (isEmpty(T))
+      return Create(T, V, T);
+    
+    assert (!T->isMutable());
+    
+    key_type_ref K = ImutInfo::KeyOfValue(V);
+    key_type_ref KCurrent = ImutInfo::KeyOfValue(Value(T));
+    
+    if (ImutInfo::isEqual(K,KCurrent))
+      return Create(Left(T), V, Right(T));
+    else if (ImutInfo::isLess(K,KCurrent))
+      return Balance(Add_internal(V,Left(T)), Value(T), Right(T));
+    else
+      return Balance(Left(T), Value(T), Add_internal(V,Right(T)));
+  }
+  
+  /// Remove_interal - Creates a new tree that includes all the data
+  ///  from the original tree except the specified data.  If the
+  ///  specified data did not exist in the original tree, the original
+  ///  tree is returned.
+  TreeTy* Remove_internal(key_type_ref K, TreeTy* T) {
+    if (isEmpty(T))
+      return T;
+    
+    assert (!T->isMutable());
+    
+    key_type_ref KCurrent = ImutInfo::KeyOfValue(Value(T));
+    
+    if (ImutInfo::isEqual(K,KCurrent))
+      return CombineLeftRightTrees(Left(T),Right(T));
+    else if (ImutInfo::isLess(K,KCurrent))
+      return Balance(Remove_internal(K,Left(T)), Value(T), Right(T));
+    else
+      return Balance(Left(T), Value(T), Remove_internal(K,Right(T)));
+  }
+  
+  TreeTy* CombineLeftRightTrees(TreeTy* L, TreeTy* R) {
+    if (isEmpty(L)) return R;      
+    if (isEmpty(R)) return L;
+    
+    TreeTy* OldNode;          
+    TreeTy* NewRight = RemoveMinBinding(R,OldNode);
+    return Balance(L,Value(OldNode),NewRight);
+  }
+  
+  TreeTy* RemoveMinBinding(TreeTy* T, TreeTy*& NodeRemoved) {
+    assert (!isEmpty(T));
+    
+    if (isEmpty(Left(T))) {
+      NodeRemoved = T;
+      return Right(T);
+    }
+    
+    return Balance(RemoveMinBinding(Left(T),NodeRemoved),Value(T),Right(T));
+  }    
+  
+  /// MarkImmutable - Clears the mutable bits of a root and all of its
+  ///  descendants.
+  void MarkImmutable(TreeTy* T) {
+    if (!T || !T->isMutable())
+      return;
+    
+    T->RemoveMutableFlag();
+    MarkImmutable(Left(T));
+    MarkImmutable(Right(T));
+  }
+};
+
+
+//===----------------------------------------------------------------------===//    
+// Trait classes for Profile information.
+//===----------------------------------------------------------------------===//
+
+/// Generic profile template.  The default behavior is to invoke the
+/// profile method of an object.  Specializations for primitive integers
+/// and generic handling of pointers is done below.
+template <typename T>
+struct ImutProfileInfo {
+  typedef const T  value_type;
+  typedef const T& value_type_ref;
+  
+  static inline void Profile(FoldingSetNodeID& ID, value_type_ref X) {
+    X.Profile(ID);
+  }  
+};
+
+/// Profile traits for integers.
+template <typename T>
+struct ImutProfileInteger {    
+  typedef const T  value_type;
+  typedef const T& value_type_ref;
+  
+  static inline void Profile(FoldingSetNodeID& ID, value_type_ref X) {
+    ID.AddInteger(X);
+  }  
+};
+
+#define PROFILE_INTEGER_INFO(X)\
+template<> struct ImutProfileInfo<X> : ImutProfileInteger<X> {};
+
+PROFILE_INTEGER_INFO(char)
+PROFILE_INTEGER_INFO(unsigned char)
+PROFILE_INTEGER_INFO(short)
+PROFILE_INTEGER_INFO(unsigned short)
+PROFILE_INTEGER_INFO(unsigned)
+PROFILE_INTEGER_INFO(signed)
+PROFILE_INTEGER_INFO(long)
+PROFILE_INTEGER_INFO(unsigned long)
+PROFILE_INTEGER_INFO(long long)
+PROFILE_INTEGER_INFO(unsigned long long)
+
+#undef PROFILE_INTEGER_INFO
+
+/// Generic profile trait for pointer types.  We treat pointers as
+/// references to unique objects.
+template <typename T>
+struct ImutProfileInfo<T*> {
+  typedef const T*   value_type;
+  typedef value_type value_type_ref;
+  
+  static inline void Profile(FoldingSetNodeID &ID, value_type_ref X) {
+    ID.AddPointer(X);
+  }
+};
+
+//===----------------------------------------------------------------------===//    
+// Trait classes that contain element comparison operators and type
+//  definitions used by ImutAVLTree, ImmutableSet, and ImmutableMap.  These
+//  inherit from the profile traits (ImutProfileInfo) to include operations
+//  for element profiling.
+//===----------------------------------------------------------------------===//
+
+
+/// ImutContainerInfo - Generic definition of comparison operations for
+///   elements of immutable containers that defaults to using
+///   std::equal_to<> and std::less<> to perform comparison of elements.
+template <typename T>
+struct ImutContainerInfo : public ImutProfileInfo<T> {
+  typedef typename ImutProfileInfo<T>::value_type      value_type;
+  typedef typename ImutProfileInfo<T>::value_type_ref  value_type_ref;
+  typedef value_type      key_type;
+  typedef value_type_ref  key_type_ref;
+  
+  static inline key_type_ref KeyOfValue(value_type_ref D) { return D; }
+  
+  static inline bool isEqual(key_type_ref LHS, key_type_ref RHS) { 
+    return std::equal_to<key_type>()(LHS,RHS);
+  }
+  
+  static inline bool isLess(key_type_ref LHS, key_type_ref RHS) {
+    return std::less<key_type>()(LHS,RHS);
+  }
+};
+
+/// ImutContainerInfo - Specialization for pointer values to treat pointers
+///  as references to unique objects.  Pointers are thus compared by
+///  their addresses.
+template <typename T>
+struct ImutContainerInfo<T*> : public ImutProfileInfo<T*> {
+  typedef typename ImutProfileInfo<T*>::value_type      value_type;
+  typedef typename ImutProfileInfo<T*>::value_type_ref  value_type_ref;
+  typedef value_type      key_type;
+  typedef value_type_ref  key_type_ref;
+  
+  static inline key_type_ref KeyOfValue(value_type_ref D) { return D; }
+  
+  static inline bool isEqual(key_type_ref LHS, key_type_ref RHS) {
+    return LHS == RHS;
+  }
+  
+  static inline bool isLess(key_type_ref LHS, key_type_ref RHS) {
+    return LHS < RHS;
+  }
+};
+
+//===----------------------------------------------------------------------===//    
+// Immutable Set
+//===----------------------------------------------------------------------===//
+
+template <typename ValT, typename ValInfo = ImutContainerInfo<ValT> >
+class ImmutableSet {
+public:
+  typedef typename ValInfo::value_type      value_type;
+  typedef typename ValInfo::value_type_ref  value_type_ref;
+  
+private:  
+  typedef ImutAVLTree<ValInfo> TreeTy;
+  TreeTy* Root;
+  
+  ImmutableSet(TreeTy* R) : Root(R) {}
+  
+public:
+  
+  class Factory {
+    typename TreeTy::Factory F;
+    
+  public:
+    Factory() {}
+    
+    ImmutableSet GetEmptySet() { return ImmutableSet(F.GetEmptyTree()); }
+    
+    ImmutableSet Add(ImmutableSet Old, value_type_ref V) {
+      return ImmutableSet(F.Add(Old.Root,V));
+    }
+    
+    ImmutableSet Remove(ImmutableSet Old, value_type_ref V) {
+      return ImmutableSet(F.Remove(Old.Root,V));
+    }
+    
+  private:
+    Factory(const Factory& RHS) {};
+    void operator=(const Factory& RHS) {};    
+  };
+  
+  friend class Factory;
+  
+  bool contains(const value_type_ref V) const {
+    return Root ? Root->contains(V) : false;
+  }
+  
+  bool operator==(ImmutableSet RHS) const {
+    return Root && RHS.Root ? Root->isEqual(*RHS.Root) : Root == RHS.Root;
+  }
+  
+  bool operator!=(ImmutableSet RHS) const {
+    return Root && RHS.Root ? Root->isNotEqual(*RHS.Root) : Root != RHS.Root;
+  }
+  
+  bool isEmpty() const { return !Root; }
+  
+  template <typename Callback>
+  void foreach(Callback& C) { if (Root) Root->foreach(C); }
+  
+  template <typename Callback>
+  void foreach() { if (Root) { Callback C; Root->foreach(C); } }
+  
+  //===--------------------------------------------------===//    
+  // For testing.
+  //===--------------------------------------------------===//  
+  
+  void verify() const { if (Root) Root->verify(); }
+  unsigned getHeight() const { return Root ? Root->getHeight() : 0; }
+};
+
+} // end namespace llvm
+
+#endif