diff --git a/include/swift/Remote/Failure.h b/include/swift/Remote/Failure.h
new file mode 100644
index 00000000000..df7d50f2453
--- /dev/null
+++ b/include/swift/Remote/Failure.h
@@ -0,0 +1,337 @@
+//===--- Failure.h - Failure to access remote memory ------------*- C++ -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2016 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file provides a simple diagnostics library for the various
+//  operations for working with a remote process.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_REMOTE_FAILURE_H
+#define SWIFT_REMOTE_FAILURE_H
+
+#include "swift/Remote/RemoteAddress.h"
+
+#include "llvm/Support/Compiler.h"
+#include <string>
+#include <cstring>
+#include <type_traits>
+
+namespace swift {
+namespace remote {
+
+class Failure {
+public:
+  /// An enum which unifies all of the failure kinds into a single namespace.
+  /// This is how kinds are stored internally.
+  enum class Kind {
+#define FAILURE(KIND, TEXT, ARGTYS) KIND,
+#include "swift/Remote/FailureKinds.def"
+  };
+
+  /// A bunch of enums for all the different kinds of failure.
+  /// Users should construct a Failure by passing Failure::KIND instead
+  /// of Failure::Kind::KIND.
+  #define FAILURE(KIND, TEXT, ARGTYS) \
+  enum KIND##_t { KIND = unsigned(Kind::KIND) };
+  #include "swift/Remote/FailureKinds.def"
+
+private:
+  // A whole lot of template machinery to validate that the right argument
+  // types were passed:
+
+  // A sequence of types.
+  template <class... Tys> struct TypeBundle {};
+
+  // A way of turning (X, Y, Z) into a TypeBundle:
+  //   typename TypeBundleForFunctionTypeParameters<void ARGS>::types
+  // Partially specialized at the end of this file.
+  template <class FnTy> struct TypeBundleForFunctionTypeParameters;
+
+  // A way of getting the expected TypeBundle of (nonce) argument types
+  // for a particular failure kind:
+  //   typename ArgTypesForFailureKind<KindTy>::types
+  // Explicitly specialized for each kind type at the end of this file.
+  template <class KindTy> struct ArgTypesForFailureKind;
+
+  // Nonce expected argument types.
+  enum ArgType_String {};
+  enum ArgType_Address {};
+
+  // A predicate that decides whether the given argument type satisfies
+  // the given nonce expected argument type.
+  template <class Expected, class Actual> struct IsAcceptableArgType {
+    static constexpr bool value = false;
+  };
+
+  template <class... Ts>
+  static void validateFailureArgsRecursive(TypeBundle<Ts...> expected,
+                                           TypeBundle<> actual) {
+    static_assert(std::is_same<decltype(expected), decltype(actual)>::value,
+                  "too few arguments to diagnostic");
+  }
+
+  template <class Expected, class... RestOfExpected,
+            class Actual, class... RestOfActual>
+  static void validateFailureArgsRecursive(
+                            TypeBundle<Expected, RestOfExpected...> expected,
+                            TypeBundle<Actual, RestOfActual...> actual) {
+    using SimplifiedActual = typename std::decay<Actual>::type;
+    static_assert(IsAcceptableArgType<Expected, SimplifiedActual>::value,
+                  "argument does no match");
+    validateFailureArgsRecursive(TypeBundle<RestOfExpected...>(),
+                                 TypeBundle<RestOfActual...>());
+  }
+
+public:
+  /// Validate that it's okay to construct a Failure with the given arguments.
+  template <class KindTy, class... ArgTys>
+  static void validateFailureArgs(KindTy ty, ArgTys &&... argTys) {
+    using ExpectedArgTypes = typename ArgTypesForFailureKind<KindTy>::types;
+    validateFailureArgsRecursive(ExpectedArgTypes(), TypeBundle<ArgTys...>());
+  }
+
+private:
+  static const char *getTextForKind(Kind kind) {
+    switch (kind) {
+#define FAILURE(KIND, TEXT, ARGTYS) \
+    case Kind::KIND: return TEXT;
+#include "swift/Remote/FailureKinds.def"    
+    }
+  }
+
+  union ArgStorage {
+    std::string String;
+    RemoteAddress Address;
+
+    ArgStorage() {}
+    ArgStorage(const ArgStorage &other) = delete;
+    ArgStorage &operator=(const ArgStorage &other) = delete;
+    ~ArgStorage() {}
+  };
+  enum class ArgStorageKind : char {
+    None,
+    String, // std::string
+    Address, // RemoteAddress
+  };
+
+  enum {
+    MaxArgs = 4
+  };
+
+  Kind TheKind;
+  ArgStorageKind ArgKinds[MaxArgs];
+  ArgStorage Args[MaxArgs];
+
+  template <unsigned Index>
+  void initArgs() {
+    static_assert(Index <= MaxArgs, "index out of bounds");
+    for (unsigned i = Index; i < MaxArgs; ++i) {
+      ArgKinds[i] = ArgStorageKind::None;
+    }
+  }
+
+  template <unsigned Index, class T, class... Ts>
+  void initArgs(T &&nextArg, Ts &&... restOfArgs) {
+    static_assert(Index < MaxArgs, "index out of bounds");
+    initArg(Index, std::forward<T>(nextArg));
+    initArgs<Index + 1>(std::forward<T>(restOfArgs)...);
+  }
+
+  void initArg(unsigned index, std::string &&string) {
+    ArgKinds[index] = ArgStorageKind::String;
+    new (&Args[index]) std::string(std::move(string));
+  }
+
+  void initArg(unsigned index, const std::string &string) {
+    ArgKinds[index] = ArgStorageKind::String;
+    new (&Args[index]) std::string(string);
+  }
+
+  void initArg(unsigned index, RemoteAddress address) {
+    ArgKinds[index] = ArgStorageKind::Address;
+    new (&Args[index]) RemoteAddress(address);
+  }
+
+public:
+  template <class KindTy, class... Ts>
+  explicit Failure(KindTy kind, Ts &&...args) : TheKind(Kind(kind)) {
+    validateFailureArgs(kind, std::forward<Ts>(args)...);
+    initArgs<0>(std::forward<Ts>(args)...);
+  }
+
+  Failure(const Failure &other) : TheKind(other.TheKind) {
+    for (unsigned i = 0; i != MaxArgs; ++i) {
+      ArgKinds[i] = other.ArgKinds[i];
+      switch (ArgKinds[i]) {
+      case ArgStorageKind::None:
+        break;
+      case ArgStorageKind::String:
+        ::new (&Args[i].String) std::string(other.Args[i].String);
+        break;
+      case ArgStorageKind::Address:
+        ::new (&Args[i].Address) RemoteAddress(other.Args[i].Address);
+        break;
+      }
+    }
+  }
+
+  Failure(Failure &&other) : TheKind(other.TheKind) {
+    for (unsigned i = 0; i != MaxArgs; ++i) {
+      ArgKinds[i] = other.ArgKinds[i];
+      switch (ArgKinds[i]) {
+      case ArgStorageKind::None:
+        break;
+      case ArgStorageKind::String:
+        ::new (&Args[i].String) std::string(std::move(other.Args[i].String));
+        break;
+      case ArgStorageKind::Address:
+        ::new (&Args[i].Address) RemoteAddress(std::move(other.Args[i].Address));
+        break;
+      }
+    }
+  }
+
+  Failure &operator=(const Failure &other) {
+    this->~Failure();
+    ::new (this) Failure(other);
+    return *this;
+  }
+
+  Failure &operator=(Failure &&other) {
+    this->~Failure();
+    ::new (this) Failure(std::move(other));
+    return *this;
+  }
+
+  ~Failure() {
+    for (unsigned i = 0; i != MaxArgs; ++i) {
+      switch (ArgKinds[i]) {
+      case ArgStorageKind::None:
+        break;
+      case ArgStorageKind::String:
+        Args[i].String.~basic_string();
+        break;
+      case ArgStorageKind::Address:
+        Args[i].Address.~RemoteAddress();
+        break;
+      }
+    }
+  }
+
+  /// Return the kind of failure.
+  Kind getKind() const { return TheKind; }
+
+  /// Return the number of arguments to the failure.
+  unsigned getNumArgs() const {
+    unsigned i = 0;
+    for (; i != MaxArgs; ++i) {
+      // Stop at the first missing argument.
+      if (ArgKinds[i] == ArgStorageKind::None)
+        break;
+    }
+    return i;
+  }
+
+  /// Render the failure as an error message.
+  std::string render() const {
+    std::string result;
+
+    const char *text = getTextForKind(TheKind);
+    while (const char *next = std::strchr(text, '%')) {
+      // Append everything we just skipped over.
+      result.append(text, next - text);
+
+      // Skip the '%'.
+      next++;
+
+      // Do something based on the character after '%'.
+      char c = *next++;
+      if (c == '%') {
+        result += c;
+        continue;
+      }
+
+      assert('0' <= c && c <= '9');
+      unsigned argIndex = c - '0';
+      assert(argIndex < MaxArgs);
+
+      switch (ArgKinds[argIndex]) {
+      case ArgStorageKind::None:
+        LLVM_BUILTIN_UNREACHABLE;
+
+      // Stringize a string argument by just appending it.
+      case ArgStorageKind::String:
+        result += Args[argIndex].String;
+        continue;
+
+      // Stringize an address argument as a hex number.  We assume that an
+      // address less than 2^32 is for a 32-bit target and accordingly
+      // only print 8 digits for it.
+      //
+      // It is really silly to provide our own hex-stringization here,
+      // but swift::remote is supposed to be a minimal, header-only library.
+      case ArgStorageKind::Address: {
+        result += '0';
+        result += 'x';
+        uint64_t address = Args[argIndex].Address.getAddressData();
+        unsigned max = ((address >> 32) != 0 ? 16 : 8);
+        for (unsigned i = 0; i != max; ++i) {
+          result += "0123456789abcdef"[(address >> (max - 1 - i) * 4) & 0xF];
+        }
+        continue;
+      }
+      }
+      LLVM_BUILTIN_UNREACHABLE;
+    }
+
+    // Append the rest of the string.
+    result.append(text);
+
+    return result;
+  }
+};
+
+template <class... Tys>
+struct Failure::TypeBundleForFunctionTypeParameters<void(Tys...)> {
+  using types = TypeBundle<Tys...>;
+};
+
+template <class... Tys> class TypeBundle {};
+
+#define FAILURE(KIND, TEXT, ARGTYS)                                      \
+template <> struct Failure::ArgTypesForFailureKind<Failure::KIND##_t> {  \
+  using String = ArgType_String;                                         \
+  using Address = ArgType_Address;                                       \
+  using types = TypeBundleForFunctionTypeParameters<void ARGTYS>::types; \
+};
+#include "swift/Remote/FailureKinds.def"
+
+template <>
+struct Failure::IsAcceptableArgType<Failure::ArgType_String, const char *> {
+  static constexpr bool value = true;
+};
+
+template <>
+struct Failure::IsAcceptableArgType<Failure::ArgType_String, std::string> {
+  static constexpr bool value = true;
+};
+
+template <>
+struct Failure::IsAcceptableArgType<Failure::ArgType_Address, RemoteAddress> {
+  static constexpr bool value = true;
+};
+
+} // end namespace remote
+} // end namespace swift
+
+#endif // SWIFT_REMOTE_FAILURE_H
+
diff --git a/include/swift/Remote/FailureKinds.def b/include/swift/Remote/FailureKinds.def
new file mode 100644
index 00000000000..bd8c022808a
--- /dev/null
+++ b/include/swift/Remote/FailureKinds.def
@@ -0,0 +1,19 @@
+//===--- FailureKinds.def - Remote failure definitions ----------*- C++ -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2016 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+// FAILURE(KIND, TEXT, ARGTYS)
+
+FAILURE(Unknown, "an unknown failure occurred", ())
+FAILURE(Memory, "an unknown failure occurred while reading %0 at address %1",
+        (String, Address))
+
+#undef FAILURE
\ No newline at end of file
diff --git a/include/swift/Remote/MemoryReader.h b/include/swift/Remote/MemoryReader.h
index 153c80141f6..3f57862401f 100644
--- a/include/swift/Remote/MemoryReader.h
+++ b/include/swift/Remote/MemoryReader.h
@@ -18,35 +18,13 @@
 #ifndef SWIFT_REMOTE_MEMORYREADER_H
 #define SWIFT_REMOTE_MEMORYREADER_H
 
-#include <cstdint>
+#include "swift/Remote/RemoteAddress.h"
+
 #include <string>
 
 namespace swift {
 namespace remote {
 
-/// An abstract address in the remote process's address space.
-class RemoteAddress {
-  uint64_t Data;
-public:
-  explicit RemoteAddress(const void *localPtr)
-    : Data(reinterpret_cast<uintptr_t>(localPtr)) {}
-
-  explicit RemoteAddress(uint64_t addressData) : Data(addressData) {}
-
-  explicit operator bool() const {
-    return Data != 0;
-  }
-
-  template <class T>
-  const T *getLocalPointer() const {
-    return reinterpret_cast<const T*>(static_cast<uintptr_t>(Data));
-  }
-
-  uint64_t getAddressData() const {
-    return Data;
-  }
-};
-
 /// An abstract interface for reading memory.
 ///
 /// This abstraction presents memory as if it were a read-only
diff --git a/include/swift/Remote/RemoteAddress.h b/include/swift/Remote/RemoteAddress.h
new file mode 100644
index 00000000000..115b3c063ac
--- /dev/null
+++ b/include/swift/Remote/RemoteAddress.h
@@ -0,0 +1,53 @@
+//===--- RemoteAddress.h - Address of remote memory -------------*- C++ -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2016 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file defines the RemoteAddress type, which abstracts over an
+//  address in a remote process.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_REMOTE_REMOTEADDRESS_H
+#define SWIFT_REMOTE_REMOTEADDRESS_H
+
+#include <cstdint>
+
+namespace swift {
+namespace remote {
+
+/// An abstract address in the remote process's address space.
+class RemoteAddress {
+  uint64_t Data;
+public:
+  explicit RemoteAddress(const void *localPtr)
+    : Data(reinterpret_cast<uintptr_t>(localPtr)) {}
+
+  explicit RemoteAddress(uint64_t addressData) : Data(addressData) {}
+
+  explicit operator bool() const {
+    return Data != 0;
+  }
+
+  template <class T>
+  const T *getLocalPointer() const {
+    return reinterpret_cast<const T*>(static_cast<uintptr_t>(Data));
+  }
+
+  uint64_t getAddressData() const {
+    return Data;
+  }
+};
+
+} // end namespace remote
+} // end namespace swift
+
+#endif // SWIFT_REMOTE_REMOTEADDRESS_H
+
diff --git a/include/swift/RemoteAST/RemoteAST.h b/include/swift/RemoteAST/RemoteAST.h
index ebcaa9ccd4f..2c52b9f4aa1 100644
--- a/include/swift/RemoteAST/RemoteAST.h
+++ b/include/swift/RemoteAST/RemoteAST.h
@@ -19,6 +19,7 @@
 #ifndef SWIFT_REMOTEAST_REMOTEAST_H
 #define SWIFT_REMOTEAST_REMOTEAST_H
 
+#include "swift/Remote/Failure.h"
 #include "swift/Remote/MemoryReader.h"
 #include "swift/Basic/LLVM.h"
 #include "llvm/ADT/Optional.h"
@@ -33,6 +34,107 @@ class Type;
 
 namespace remoteAST {
 
+template <class T>
+class Result {
+  union Storage {
+    remote::Failure Failure;
+    T Success;
+
+    Storage() {}
+    Storage(const Storage &) = delete;
+    Storage &operator=(const Storage &) = delete;
+    ~Storage() {}
+  };
+
+  Storage S;
+  bool IsSuccess;
+
+  Result(bool isSuccess) {}
+
+public:
+  /*implicit*/ Result(const T &value) : IsSuccess(true) {
+    new (&S.Success) T(value);
+  }
+
+  /*implicit*/ Result(T &&value) : IsSuccess(true) {
+    new (&S.Success) T(std::move(value));
+  }
+
+  /*implicit*/ Result(remote::Failure &&failure) : IsSuccess(false) {
+    new (&S.Failure) remote::Failure(std::move(failure));
+  }
+
+  Result(const Result &other) : IsSuccess(other.IsSuccess) {
+    if (IsSuccess) {
+      ::new (&S.Success) T(other.S.Success);
+    } else {
+      ::new (&S.Failure) remote::Failure(other.S.Failure);      
+    }
+  }
+
+  Result(Result &&other) : IsSuccess(other.IsSuccess) {
+    if (IsSuccess) {
+      ::new (&S.Success) T(std::move(other.S.Success));
+    } else {
+      ::new (&S.Failure) remote::Failure(std::move(other.S.Failure));
+    }
+  }
+
+  Result &operator=(const Result &other) {
+    this->~Result();
+    ::new (this) Result(other);
+    return *this;
+  }
+
+  Result &operator=(Result &&other) {
+    this->~Result();
+    ::new (this) Result(std::move(other));
+    return *this;
+  }
+
+  ~Result() {
+    if (IsSuccess) {
+      S.Success.~T();
+    } else {
+      S.Failure.~Failure();
+    }
+  }
+
+  template <class... ArgTys>
+  static Result emplaceSuccess(ArgTys &&...args) {
+    Result result(true);
+    ::new (&result.S.Success) T(std::forward<ArgTys>(args)...);
+    return result;
+  }
+
+  template <class KindTy, class... ArgTys>
+  static Result emplaceFailure(KindTy kind, ArgTys &&...args) {
+    Result result(false);
+    ::new (&result.S.Failure)
+      remote::Failure(kind, std::forward<ArgTys>(args)...);
+    return result;
+  }
+
+  explicit operator bool() const { return isSuccess(); }
+  bool isSuccess() const { return IsSuccess; }
+  bool isFailure() const { return !IsSuccess; }
+
+  const remote::Failure &getFailure() const {
+    assert(isFailure());
+    return S.Failure;
+  }
+
+  const T &getValue() const & {
+    assert(isSuccess());
+    return S.Success;
+  }
+
+  T &&getValue() && {
+    assert(isSuccess());
+    return std::move(S.Success);
+  }
+};
+
 /// A context for performing an operation relating the remote process with
 /// the AST.  This may be discarded and recreated at any time without danger,
 /// but reusing a context across multiple calls may allow some redundant work
@@ -65,16 +167,12 @@ public:
 
   /// Given an address which is supposedly of type metadata, try to
   /// resolve it to a specific type in the local AST.
-  ///
-  /// This may fail by returning a null type.
-  Type getTypeForRemoteTypeMetadata(remote::RemoteAddress address);
+  Result<Type> getTypeForRemoteTypeMetadata(remote::RemoteAddress address);
 
   /// Given an address which is supposedly of a nominal type descriptor,
   /// try to resolve it to a specific nominal type declaration in the
   /// local AST.
-  ///
-  /// This may fail by returning null.
-  NominalTypeDecl *
+  Result<NominalTypeDecl *>
   getDeclForRemoteNominalTypeDescriptor(remote::RemoteAddress address);
 
   /// Given a type in the local AST, try to resolve the offset of its
@@ -83,7 +181,7 @@ public:
   /// This may fail by returning an empty optional.  Failure may indicate
   /// that an offset for the property could not be resolved, or it may
   /// simply indicate that the property has a non-zero offset.
-  Optional<uint64_t> getOffsetForProperty(Type type, StringRef propertyName);
+  Result<uint64_t> getOffsetForProperty(Type type, StringRef propertyName);
 };
 
 } // end namespace remoteAST
diff --git a/lib/RemoteAST/RemoteAST.cpp b/lib/RemoteAST/RemoteAST.cpp
index 4be99a6006b..607bef02437 100644
--- a/lib/RemoteAST/RemoteAST.cpp
+++ b/lib/RemoteAST/RemoteAST.cpp
@@ -506,26 +506,33 @@ public:
     }
   }
 
-  Type getTypeForRemoteTypeMetadata(RemoteAddress address) {
+  Result<Type> getTypeForRemoteTypeMetadata(RemoteAddress address) {
+    Type result;
     if (Is32) {
-      return Reader32->readTypeFromMetadata(address.getAddressData());
+      result = Reader32->readTypeFromMetadata(address.getAddressData());
     } else {
-      return Reader64->readTypeFromMetadata(address.getAddressData());
+      result = Reader64->readTypeFromMetadata(address.getAddressData());
     }
+    if (result) return result;
+    return Result<Type>::emplaceFailure(Failure::Unknown);
   }
 
-  NominalTypeDecl *getDeclForRemoteNominalTypeDescriptor(RemoteAddress address){
-
+  Result<NominalTypeDecl *>
+  getDeclForRemoteNominalTypeDescriptor(RemoteAddress address) {
+    NominalTypeDecl *result;
     if (Is32) {
-      return Reader32->readNominalTypeFromDescriptor(address.getAddressData());
+      result =Reader32->readNominalTypeFromDescriptor(address.getAddressData());
     } else {
-      return Reader64->readNominalTypeFromDescriptor(address.getAddressData());
+      result =Reader64->readNominalTypeFromDescriptor(address.getAddressData());
     }
+
+    if (result) return result;
+    return Result<NominalTypeDecl *>::emplaceFailure(Failure::Unknown);
   }
 
-  Optional<uint64_t> getOffsetForProperty(Type type, StringRef propertyName) {
+  Result<uint64_t> getOffsetForProperty(Type type, StringRef propertyName) {
     // TODO
-    return None;    
+    return Result<uint64_t>::emplaceFailure(Failure::Unknown);
   }
 };
 
@@ -544,16 +551,17 @@ RemoteASTContext::~RemoteASTContext() {
   delete asImpl(Impl);
 }
 
-Type RemoteASTContext::getTypeForRemoteTypeMetadata(RemoteAddress address) {
+Result<Type>
+RemoteASTContext::getTypeForRemoteTypeMetadata(RemoteAddress address) {
   return asImpl(Impl)->getTypeForRemoteTypeMetadata(address);
 }
 
-NominalTypeDecl *
+Result<NominalTypeDecl *>
 RemoteASTContext::getDeclForRemoteNominalTypeDescriptor(RemoteAddress address) {
   return asImpl(Impl)->getDeclForRemoteNominalTypeDescriptor(address);
 }
 
-Optional<uint64_t>
+Result<uint64_t>
 RemoteASTContext::getOffsetForProperty(Type type, StringRef propertyName) {
   return asImpl(Impl)->getOffsetForProperty(type, propertyName);
 }