diff --git a/c++/src/capnp/compiler/capnpc2.c++ b/c++/src/capnp/compiler/capnpc2.c++
index 56c9013..8f0b825 100644
--- a/c++/src/capnp/compiler/capnpc2.c++
+++ b/c++/src/capnp/compiler/capnpc2.c++
@@ -24,6 +24,7 @@
 #include "lexer.h"
 #include "parser.h"
 #include "compiler.h"
+#include "module-loader.h"
 #include <capnp/pretty-print.h>
 #include <kj/vector.h>
 #include <kj/io.h>
@@ -31,6 +32,10 @@
 #include <kj/debug.h>
 #include "../message.h"
 #include <iostream>
+#include <kj/main.h>
+
+namespace capnp {
+namespace compiler {
 
 class DummyModule: public capnp::compiler::Module {
 public:
@@ -53,6 +58,36 @@
   }
 };
 
+class CompilerMain {
+public:
+  explicit CompilerMain(kj::ProcessContext& context)
+      : context(context), loader(STDERR_FILENO) {}
+
+  kj::MainFunc getMain() {
+    return kj::MainBuilder(
+          context, "Cap'n Proto compiler version 0.2",
+          "Compiles Cap'n Proto schema files and generates corresponding source code in one or "
+          "more languages.")
+        .expectOneOrMoreArgs("source", KJ_BIND_METHOD(*this, addSource))
+        .build();
+  }
+
+  kj::MainBuilder::Validity addSource(kj::StringPtr file) {
+    KJ_IF_MAYBE(module, loader.loadModule(file, file)) {
+      compiler.add(*module, Compiler::EAGER);
+    } else {
+      return "no such file";
+    }
+
+    return true;
+  }
+
+private:
+  kj::ProcessContext& context;
+  ModuleLoader loader;
+  Compiler compiler;
+};
+
 int main(int argc, char* argv[]) {
   // Eventually this will be capnpc.  For now it's just a dummy program that tests parsing.
 
@@ -109,3 +144,8 @@
 
   return 0;
 }
+
+}  // namespace compiler
+}  // namespace capnp
+
+KJ_MAIN(capnp::compiler::CompilerMain);
diff --git a/c++/src/capnp/compiler/compiler.c++ b/c++/src/capnp/compiler/compiler.c++
index 9a2c03c..e3f9e53 100644
--- a/c++/src/capnp/compiler/compiler.c++
+++ b/c++/src/capnp/compiler/compiler.c++
@@ -81,7 +81,7 @@
   kj::Maybe<const Node&> lookup(const DeclName::Reader& name) const;
   // Resolve an arbitrary DeclName to a Node.
 
-  kj::Maybe<Schema> getBootstrapOrFinalSchema() const;
+  kj::Maybe<Schema> getBootstrapSchema() const;
   kj::Maybe<Schema> getFinalSchema() const;
 
   void traverse(Compiler::Mode mode) const;
@@ -93,7 +93,7 @@
 
   // implements NodeTranslator::Resolver -----------------------------
   kj::Maybe<ResolvedName> resolve(const DeclName::Reader& name) const override;
-  kj::Maybe<Schema> resolveMaybeBootstrapSchema(uint64_t id) const override;
+  kj::Maybe<Schema> resolveBootstrapSchema(uint64_t id) const override;
   kj::Maybe<Schema> resolveFinalSchema(uint64_t id) const override;
 
 private:
@@ -212,7 +212,7 @@
   Impl();
   virtual ~Impl();
 
-  uint64_t add(Module& module, Mode mode) const;
+  uint64_t add(const Module& module, Mode mode) const;
   const CompiledModule& add(const Module& parsedModule) const;
 
   struct Workspace {
@@ -473,8 +473,8 @@
             locked->translator->getBootstrapNode());
       })) {
         locked->bootstrapSchema = nullptr;
-        addError(kj::str("Internal compiler bug: Bootstrap schema failed validation: ",
-                         exception->getDescription()));
+        addError(kj::str("Internal compiler bug: Bootstrap schema failed validation:\n",
+                         *exception));
       }
 
       // If the Workspace is destroyed while this Node is still in the BOOTSTRAP state,
@@ -500,8 +500,8 @@
             locked->translator->finish());
       })) {
         locked->finalSchema = nullptr;
-        addError(kj::str("Internal compiler bug: Schema failed validation: ",
-                         exception->getDescription()));
+        addError(kj::str("Internal compiler bug: Schema failed validation:\n",
+                         *exception));
       }
 
       locked->advanceState(Content::FINISHED);
@@ -605,12 +605,19 @@
   return *node;
 }
 
-kj::Maybe<Schema> Compiler::Node::getBootstrapOrFinalSchema() const {
+kj::Maybe<Schema> Compiler::Node::getBootstrapSchema() const {
   auto& content = getContent(Content::BOOTSTRAP);
 
   if (__atomic_load_n(&content.state, __ATOMIC_ACQUIRE) == Content::FINISHED &&
-      content.finalSchema != nullptr) {
-    return content.finalSchema;
+      content.bootstrapSchema == nullptr) {
+    // The bootstrap schema was discarded.  Copy it from the final schema.
+    // (We can't just return the final schema because using it could trigger schema loader
+    // callbacks that would deadlock.)
+    KJ_IF_MAYBE(finalSchema, content.finalSchema) {
+      return module->getCompiler().getWorkspace().bootstrapLoader.loadOnce(finalSchema->getProto());
+    } else {
+      return nullptr;
+    }
   } else {
     return content.bootstrapSchema;
   }
@@ -640,9 +647,9 @@
   });
 }
 
-kj::Maybe<Schema> Compiler::Node::resolveMaybeBootstrapSchema(uint64_t id) const {
+kj::Maybe<Schema> Compiler::Node::resolveBootstrapSchema(uint64_t id) const {
   KJ_IF_MAYBE(node, module->getCompiler().findNode(id)) {
-    return node->getBootstrapOrFinalSchema();
+    return node->getBootstrapSchema();
   } else {
     KJ_FAIL_REQUIRE("Tried to get schema for ID we haven't seen before.");
   }
@@ -743,7 +750,7 @@
   }
 }
 
-uint64_t Compiler::Impl::add(Module& module, Mode mode) const {
+uint64_t Compiler::Impl::add(const Module& module, Mode mode) const {
   Impl::Workspace workspace;
   auto lock = this->workspace.lockExclusive();
   *lock = &workspace;
@@ -766,7 +773,7 @@
       node->getFinalSchema();
     } else {
       // Must be the bootstrap loader.
-      node->getBootstrapOrFinalSchema();
+      node->getBootstrapSchema();
     }
   }
 }
@@ -776,7 +783,7 @@
 Compiler::Compiler(): impl(kj::heap<Impl>()) {}
 Compiler::~Compiler() {}
 
-uint64_t Compiler::add(Module& module, Mode mode) const {
+uint64_t Compiler::add(const Module& module, Mode mode) const {
   return impl->add(module, mode);
 }
 
diff --git a/c++/src/capnp/compiler/compiler.h b/c++/src/capnp/compiler/compiler.h
index f1cd939..eea4a25 100644
--- a/c++/src/capnp/compiler/compiler.h
+++ b/c++/src/capnp/compiler/compiler.h
@@ -76,7 +76,7 @@
     // use EAGER mode.
   };
 
-  uint64_t add(Module& module, Mode mode) const;
+  uint64_t add(const Module& module, Mode mode) const;
   // Add a module to the Compiler, returning the module's file ID.  The ID can then be used to
   // look up the schema in the SchemaLoader returned by `getLoader()`.  However, if there were any
   // errors while compiling (reported via `module.addError()`), then the SchemaLoader may behave as
diff --git a/c++/src/capnp/compiler/module-loader.c++ b/c++/src/capnp/compiler/module-loader.c++
index 47b9ebb..fd4a4b1 100644
--- a/c++/src/capnp/compiler/module-loader.c++
+++ b/c++/src/capnp/compiler/module-loader.c++
@@ -263,7 +263,7 @@
     uint startLine = findLargestElementBefore(lines, startByte);
     uint startCol = startByte - lines[startLine];
     loader.writeError(
-        kj::str(localName, ":", startLine, ":", startCol, ": error: ", message, "\n"));
+        kj::str(localName, ":", startLine + 1, ":", startCol + 1, ": error: ", message, "\n"));
   }
 
 private:
@@ -291,7 +291,7 @@
     return *iter->second;
   }
 
-  if (access(canonicalLocalName.cStr(), R_OK) < 0) {
+  if (access(canonicalLocalName.cStr(), F_OK) < 0) {
     // No such file.
     return nullptr;
   }
diff --git a/c++/src/capnp/compiler/node-translator.c++ b/c++/src/capnp/compiler/node-translator.c++
index 99830a6..778525e 100644
--- a/c++/src/capnp/compiler/node-translator.c++
+++ b/c++/src/capnp/compiler/node-translator.c++
@@ -1489,8 +1489,7 @@
       }
       break;
     case schema::Type::Body::STRUCT_TYPE:
-      KJ_IF_MAYBE(structSchema, resolver.resolveMaybeBootstrapSchema(
-          type.getBody().getStructType())) {
+      KJ_IF_MAYBE(structSchema, resolver.resolveBootstrapSchema(type.getBody().getStructType())) {
         DynamicSlot slot(valueUnion, member, structSchema->asStruct());
         compileValue(source, slot, isBootstrap);
       }
@@ -1527,7 +1526,7 @@
         kj::StringPtr id = name.getBase().getRelativeName().getValue();
 
         KJ_IF_MAYBE(enumId, dst.getEnumType()) {
-          KJ_IF_MAYBE(enumSchema, resolver.resolveMaybeBootstrapSchema(*enumId)) {
+          KJ_IF_MAYBE(enumSchema, resolver.resolveBootstrapSchema(*enumId)) {
             KJ_IF_MAYBE(enumerant, enumSchema->asEnum().findEnumerantByName(id)) {
               dst.set(DynamicEnum(*enumerant));
               wasSet = true;
@@ -1677,7 +1676,7 @@
     // We need to be very careful not to query this Schema's dependencies because if it is
     // a final schema then this query could trigger a lazy load which would deadlock.
     kj::Maybe<Schema> maybeConstSchema = isBootstrap ?
-        resolver.resolveMaybeBootstrapSchema(resolved->id) :
+        resolver.resolveBootstrapSchema(resolved->id) :
         resolver.resolveFinalSchema(resolved->id);
     KJ_IF_MAYBE(constSchema, maybeConstSchema) {
       auto constReader = constSchema->getProto().getBody().getConstNode();
@@ -1689,7 +1688,7 @@
         auto constType = constReader.getType();
         switch (constType.getBody().which()) {
           case schema::Type::Body::STRUCT_TYPE:
-            KJ_IF_MAYBE(structSchema, resolver.resolveMaybeBootstrapSchema(
+            KJ_IF_MAYBE(structSchema, resolver.resolveBootstrapSchema(
                 constType.getBody().getStructType())) {
               constValue = objValue.as(structSchema->asStruct());
             } else {
@@ -1719,7 +1718,7 @@
         // A fully unqualified identifier looks like it might refer to a constant visible in the
         // current scope, but if that's really what the user wanted, we want them to use a
         // qualified name to make it more obvious.  Report an error.
-        KJ_IF_MAYBE(scope, resolver.resolveMaybeBootstrapSchema(
+        KJ_IF_MAYBE(scope, resolver.resolveBootstrapSchema(
             constSchema->getProto().getScopeId())) {
           auto scopeReader = scope->getProto();
           kj::StringPtr parent;
@@ -1752,19 +1751,19 @@
   auto body = elementType.getBody();
   switch (body.which()) {
     case schema::Type::Body::ENUM_TYPE:
-      KJ_IF_MAYBE(enumSchema, resolver.resolveMaybeBootstrapSchema(body.getEnumType())) {
+      KJ_IF_MAYBE(enumSchema, resolver.resolveBootstrapSchema(body.getEnumType())) {
         return ListSchema::of(enumSchema->asEnum());
       } else {
         return nullptr;
       }
     case schema::Type::Body::STRUCT_TYPE:
-      KJ_IF_MAYBE(structSchema, resolver.resolveMaybeBootstrapSchema(body.getStructType())) {
+      KJ_IF_MAYBE(structSchema, resolver.resolveBootstrapSchema(body.getStructType())) {
         return ListSchema::of(structSchema->asStruct());
       } else {
         return nullptr;
       }
     case schema::Type::Body::INTERFACE_TYPE:
-      KJ_IF_MAYBE(interfaceSchema, resolver.resolveMaybeBootstrapSchema(body.getInterfaceType())) {
+      KJ_IF_MAYBE(interfaceSchema, resolver.resolveBootstrapSchema(body.getInterfaceType())) {
         return ListSchema::of(interfaceSchema->asInterface());
       } else {
         return nullptr;
@@ -1806,7 +1805,7 @@
             "'", declNameString(name), "' is not an annotation."));
       } else {
         annotationBuilder.setId(decl->id);
-        KJ_IF_MAYBE(annotationSchema, resolver.resolveMaybeBootstrapSchema(decl->id)) {
+        KJ_IF_MAYBE(annotationSchema, resolver.resolveBootstrapSchema(decl->id)) {
           auto node = annotationSchema->getProto().getBody().getAnnotationNode();
           if (!toDynamic(node).get(targetsFlagName).as<bool>()) {
             errorReporter.addErrorOn(name, kj::str(
diff --git a/c++/src/capnp/compiler/node-translator.h b/c++/src/capnp/compiler/node-translator.h
index de843fe..eb1a233 100644
--- a/c++/src/capnp/compiler/node-translator.h
+++ b/c++/src/capnp/compiler/node-translator.h
@@ -54,17 +54,24 @@
     // Look up the given name, relative to this node, and return basic information about the
     // target.
 
-    virtual kj::Maybe<Schema> resolveMaybeBootstrapSchema(uint64_t id) const = 0;
-    // Get the schema for the given ID.  Returning either a bootstrap schema or a final schema
-    // is acceptable.  Throws an exception if the id is not one that was found by calling resolve()
-    // or by traversing other schemas.  Returns null if the ID is recognized, but the corresponding
+    virtual kj::Maybe<Schema> resolveBootstrapSchema(uint64_t id) const = 0;
+    // Get the schema for the given ID.  If a schema is returned, it must be safe to traverse its
+    // dependencies using Schema::getDependency().  A schema that is only at the bootstrap stage
+    // is acceptable.
+    //
+    // Throws an exception if the id is not one that was found by calling resolve() or by
+    // traversing other schemas.  Returns null if the ID is recognized, but the corresponding
     // schema node failed to be built for reasons that were already reported.
 
     virtual kj::Maybe<Schema> resolveFinalSchema(uint64_t id) const = 0;
-    // Get the final schema for the given ID.  A bootstrap schema is not acceptable.  Throws an
-    // exception if the id is not one that was found by calling resolve() or by traversing other
-    // schemas.  Returns null if the ID is recognized, but the corresponding schema node failed to
-    // be built for reasons that were already reported.
+    // Get the final schema for the given ID.  A bootstrap schema is not acceptable.  It is NOT
+    // safe to traverse the schema's dependencies with Schema::getDependency() as doing so may
+    // trigger lazy loading callbacks that deadlock on the compiler mutex.  Instead, the caller
+    // should carefully look up dependencies through this Resolver.
+    //
+    // Throws an exception if the id is not one that was found by calling resolve() or by
+    // traversing other schemas.  Returns null if the ID is recognized, but the corresponding
+    // schema node failed to be built for reasons that were already reported.
   };
 
   NodeTranslator(const Resolver& resolver, const ErrorReporter& errorReporter,
diff --git a/c++/src/capnp/compiler/parser.c++ b/c++/src/capnp/compiler/parser.c++
index ee948f6..a691e91 100644
--- a/c++/src/capnp/compiler/parser.c++
+++ b/c++/src/capnp/compiler/parser.c++
@@ -583,11 +583,23 @@
   // -----------------------------------------------------------------
 
   parsers.usingDecl = arena.copy(p::transform(
-      p::sequence(keyword("using"), identifier, op("="), parsers.declName),
-      [this](Located<Text::Reader>&& name, Orphan<DeclName>&& target) -> DeclParserResult {
+      p::sequence(keyword("using"), p::optional(p::sequence(identifier, op("="))),
+                  parsers.declName),
+      [this](kj::Maybe<Located<Text::Reader>>&& name, Orphan<DeclName>&& target)
+          -> DeclParserResult {
         auto decl = orphanage.newOrphan<Declaration>();
         auto builder = decl.get();
-        name.copyTo(builder.initName());
+        KJ_IF_MAYBE(n, name) {
+          n->copyTo(builder.initName());
+        } else {
+          auto targetPath = target.getReader().getMemberPath();
+          if (targetPath.size() == 0) {
+            errorReporter.addErrorOn(
+                target.getReader(), "'using' declaration without '=' must use a qualified path.");
+          } else {
+            builder.setName(targetPath[targetPath.size() - 1]);
+          }
+        }
         // no id, no annotations for using decl
         builder.getBody().initUsingDecl().adoptTarget(kj::mv(target));
         return DeclParserResult(kj::mv(decl));
diff --git a/c++/src/kj/array.c++ b/c++/src/kj/array.c++
index dd01469..53f8ed6 100644
--- a/c++/src/kj/array.c++
+++ b/c++/src/kj/array.c++
@@ -54,6 +54,12 @@
   }
 }
 
+const NullArrayDisposer NullArrayDisposer::instance = NullArrayDisposer();
+
+void NullArrayDisposer::disposeImpl(
+    void* firstElement, size_t elementSize, size_t elementCount,
+    size_t capacity, void (*destroyElement)(void*)) const {}
+
 namespace _ {  // private
 
 void* HeapArrayDisposer::allocateImpl(size_t elementSize, size_t elementCount, size_t capacity,
diff --git a/c++/src/kj/array.h b/c++/src/kj/array.h
index 2f7e86b..0bd0233 100644
--- a/c++/src/kj/array.h
+++ b/c++/src/kj/array.h
@@ -108,6 +108,17 @@
                    size_t capacity, void (*destroyElement)(void*)) const override;
 };
 
+class NullArrayDisposer: public ArrayDisposer {
+  // An ArrayDisposer that does nothing.  Can be used to construct a fake Arrays that doesn't
+  // actually own its content.
+
+public:
+  static const NullArrayDisposer instance;
+
+  void disposeImpl(void* firstElement, size_t elementSize, size_t elementCount,
+                   size_t capacity, void (*destroyElement)(void*)) const override;
+};
+
 // =======================================================================================
 // Array
 
diff --git a/c++/src/kj/function-test.c++ b/c++/src/kj/function-test.c++
new file mode 100644
index 0000000..ce1ee75
--- /dev/null
+++ b/c++/src/kj/function-test.c++
@@ -0,0 +1,83 @@
+// Copyright (c) 2013, Kenton Varda <temporal@gmail.com>
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this
+//    list of conditions and the following disclaimer.
+// 2. Redistributions in binary form must reproduce the above copyright notice,
+//    this list of conditions and the following disclaimer in the documentation
+//    and/or other materials provided with the distribution.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+// ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+// (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+// LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+// ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include "function.h"
+#include <gtest/gtest.h>
+
+namespace kj {
+namespace {
+
+TEST(Function, Lambda) {
+  int i = 0;
+
+  Function<int(int, int)> f = [&](int a, int b) { return a + b + i++; };
+
+  EXPECT_EQ(123 + 456, f(123, 456));
+  EXPECT_EQ(7 + 8 + 1, f(7, 8));
+  EXPECT_EQ(9 + 2 + 2, f(2, 9));
+
+  EXPECT_EQ(i, 3);
+}
+
+struct TestType {
+  int callCount;
+
+  TestType(int callCount = 0): callCount(callCount) {}
+
+  ~TestType() { callCount = 1234; }
+  // Make sure we catch invalid post-destruction uses.
+
+  int foo(int a, int b) {
+    return a + b + callCount++;
+  }
+};
+
+TEST(Function, Method) {
+  TestType obj;
+  Function<int(int, int)> f = KJ_BIND_METHOD(obj, foo);
+  Function<uint(uint, uint)> f2 = KJ_BIND_METHOD(obj, foo);
+
+  EXPECT_EQ(123 + 456, f(123, 456));
+  EXPECT_EQ(7 + 8 + 1, f(7, 8));
+  EXPECT_EQ(9 + 2 + 2, f2(2, 9));
+
+  EXPECT_EQ(3, obj.callCount);
+
+  // Bind to a temporary.
+  f = KJ_BIND_METHOD(TestType(10), foo);
+
+  EXPECT_EQ(123 + 456 + 10, f(123, 456));
+  EXPECT_EQ(7 + 8 + 11, f(7, 8));
+  EXPECT_EQ(9 + 2 + 12, f(2, 9));
+
+  // Bind to a move.
+  f = KJ_BIND_METHOD(kj::mv(obj), foo);
+  obj.callCount = 1234;
+
+  EXPECT_EQ(123 + 456 + 3, f(123, 456));
+  EXPECT_EQ(7 + 8 + 4, f(7, 8));
+  EXPECT_EQ(9 + 2 + 5, f(2, 9));
+}
+
+} // namespace
+} // namespace kj
diff --git a/c++/src/kj/function.h b/c++/src/kj/function.h
new file mode 100644
index 0000000..bdb8428
--- /dev/null
+++ b/c++/src/kj/function.h
@@ -0,0 +1,155 @@
+// Copyright (c) 2013, Kenton Varda <temporal@gmail.com>
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this
+//    list of conditions and the following disclaimer.
+// 2. Redistributions in binary form must reproduce the above copyright notice,
+//    this list of conditions and the following disclaimer in the documentation
+//    and/or other materials provided with the distribution.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+// ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+// (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+// LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+// ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef KJ_FUNCTION_H_
+#define KJ_FUNCTION_H_
+
+#include "memory.h"
+
+namespace kj {
+
+template <typename Signature>
+class Function;
+// Function wrapper using virtual-based polymorphism.  Use this when template polymorphism is
+// not possible.  You can, for example, accept a Function as a parameter:
+//
+//     void setFilter(Function<bool(const Widget&)> filter);
+//
+// The caller of `setFilter()` may then pass any callable object as the parameter.  The callable
+// object does not have to have the exact signature specified, just one that is "compatible" --
+// i.e. the return type is covariant and the parameters are contravariant.
+//
+// Unlike `std::function`, `kj::Function`s are movable but not copyable, just like `kj::Own`.  This
+// is to avoid unexpected heap allocation or slow atomic reference counting.
+//
+// When a `Function` is constructed from an lvalue, it captures only a reference to the value.
+// When constructed from an rvalue, it invokes the value's move constructor.  So, for example:
+//
+//     struct AddN {
+//       int n;
+//       int operator(int i) { return i + n; }
+//     }
+//
+//     Function<int(int, int)> f1 = AddN{2};
+//     // f1 owns an instance of AddN.  It may safely be moved out
+//     // of the local scope.
+//
+//     AddN adder(2);
+//     Function<int(int, int)> f2 = adder;
+//     // f2 contains a reference to `adder`.  Thus, it becomes invalid
+//     // when `adder` goes out-of-scope.
+//
+//     AddN adder2(2);
+//     Function<int(int, int)> f3 = kj::mv(adder2);
+//     // f3 owns an insatnce of AddN moved from `adder2`.  f3 may safely
+//     // be moved out of the local scope.
+//
+// Additionally, a Function may be bound to a class method using KJ_BIND_METHOD(object, methodName).
+// For example:
+//
+//     class Printer {
+//     public:
+//       void print(int i);
+//       void print(kj::StringPtr s);
+//     };
+//
+//     Printer p;
+//
+//     Function<void(uint)> intPrinter = KJ_BIND_METHOD(p, print);
+//     // Will call Printer::print(int).
+//
+//     Function<void(const char*)> strPrinter = KJ_BIND_METHOD(p, print);
+//     // Will call Printer::print(kj::StringPtr).
+//
+// Notice how KJ_BIND_METHOD is able to figure out which overload to use depending on the kind of
+// Function it is binding to.
+
+template <typename Return, typename... Params>
+class Function<Return(Params...)> {
+public:
+  template <typename F>
+  inline Function(F&& f): impl(heap<Impl<F>>(kj::fwd<F>(f))) {}
+  Function() = default;
+
+  inline Return operator()(Params... params) {
+    return (*impl)(kj::fwd<Params>(params)...);
+  }
+
+private:
+  class Iface {
+  public:
+    virtual Return operator()(Params... params) = 0;
+  };
+
+  template <typename F>
+  class Impl final: public Iface {
+  public:
+    explicit Impl(F&& f): f(kj::fwd<F>(f)) {}
+
+    Return operator()(Params... params) override {
+      return f(kj::fwd<Params>(params)...);
+    }
+
+  private:
+    F f;
+  };
+
+  Own<Iface> impl;
+};
+
+namespace _ {
+
+template <typename T>
+T rvalueOrRef(T&&);
+// Hack to help detect if an expression is an lvalue or an rvalue.
+//
+//     int i;
+//     decltype(i) i1(i);                              // i1 has type int.
+//     decltype(rvalueOrRef(i)) i2(i);                 // i2 has type int&.
+//     decltype(rvalueOrRef(kj::mv(i)) i3(kj::mv(i));  // i3 has type int.
+
+}  // namespace _
+
+#define KJ_BIND_METHOD(obj, method) \
+  ({ \
+    typedef decltype(::kj::_::rvalueOrRef(obj)) T; \
+    class F { \
+    public: \
+      inline F(T&& t): t(::kj::fwd<T>(t)) {} \
+      template <typename... Params> \
+      auto operator()(Params&&... params) \
+          -> decltype(::kj::instance<T>().method(::kj::fwd<Params>(params)...)) { \
+        return t.method(::kj::fwd<Params>(params)...); \
+      } \
+    private: \
+      T t; \
+    }; \
+    (F(obj)); \
+  })
+// Macro that produces a functor object which forwards to the method `obj.name`.  If `obj` is an
+// lvalue, the functor will hold a reference to it.  If `obj` is an rvalue, the functor will
+// contain a copy (by move) of it.
+
+}  // namespace kj
+
+#endif  // KJ_FUNCTION_H_
diff --git a/c++/src/kj/main.c++ b/c++/src/kj/main.c++
new file mode 100644
index 0000000..8707b53
--- /dev/null
+++ b/c++/src/kj/main.c++
@@ -0,0 +1,685 @@
+// Copyright (c) 2013, Kenton Varda <temporal@gmail.com>
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this
+//    list of conditions and the following disclaimer.
+// 2. Redistributions in binary form must reproduce the above copyright notice,
+//    this list of conditions and the following disclaimer in the documentation
+//    and/or other materials provided with the distribution.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+// ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+// (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+// LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+// ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include "main.h"
+#include "debug.h"
+#include "arena.h"
+#include <map>
+#include <set>
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+#include <limits.h>
+
+namespace kj {
+
+// =======================================================================================
+
+TopLevelProcessContext::TopLevelProcessContext(StringPtr programName)
+    : programName(programName),
+      cleanShutdown(getenv("KJ_CLEAN_SHUTDOWN") != nullptr) {}
+
+StringPtr TopLevelProcessContext::getProgramName() {
+  return programName;
+}
+
+void TopLevelProcessContext::exit() {
+  int exitCode = hadErrors ? 1 : 0;
+  if (cleanShutdown) {
+#if KJ_NO_EXCEPTIONS
+    // This is the best we can do.
+    warning("warning: KJ_CLEAN_SHUTDOWN may not work correctly when compiled "
+            "with -fno-exceptions.");
+    ::exit(exitCode);
+#else
+    throw CleanShutdownException { exitCode };
+#endif
+  }
+  quick_exit(exitCode);
+}
+
+void TopLevelProcessContext::warning(StringPtr message) {
+  const char* pos = message.begin();
+
+  while (pos < message.end()) {
+    ssize_t n = write(STDERR_FILENO, pos, message.end() - pos);
+    if (n < 0) {
+      if (errno == EINTR) {
+        continue;
+      }
+      // Apparently we can't write to stderr.  Dunno what to do.
+      return;
+    }
+    pos += n;
+  }
+  if (message.size() > 0 && message[message.size() - 1] != '\n') {
+    write(STDERR_FILENO, "\n", 1);
+  }
+}
+
+void TopLevelProcessContext::error(StringPtr message) {
+  hadErrors = true;
+  warning(message);
+}
+
+void TopLevelProcessContext::exitError(StringPtr message) {
+  error(message);
+  exit();
+}
+
+void TopLevelProcessContext::exitInfo(StringPtr message) {
+  const char* pos = message.begin();
+
+  while (pos < message.end()) {
+    ssize_t n;
+    KJ_SYSCALL(n = write(STDOUT_FILENO, pos, message.end() - pos));
+    pos += n;
+  }
+  if (message.size() > 0 && message[message.size() - 1] != '\n') {
+    write(STDOUT_FILENO, "\n", 1);
+  }
+
+  exit();
+}
+
+void TopLevelProcessContext::increaseLoggingVerbosity() {
+  // At the moment, there is only one log level that isn't enabled by default.
+  _::Debug::setLogLevel(_::Debug::Severity::INFO);
+}
+
+// =======================================================================================
+
+int runMainAndExit(ProcessContext& context, MainFunc&& func, int argc, char* argv[]) {
+#if !KJ_NO_EXCEPTIONS
+  try {
+#endif
+    KJ_ASSERT(argc > 0);
+
+    KJ_STACK_ARRAY(StringPtr, params, argc - 1, 8, 32);
+    for (int i = 1; i < argc; i++) {
+      params[i - 1] = argv[i];
+    }
+
+    KJ_IF_MAYBE(exception, runCatchingExceptions([&]() {
+      func(argv[0], params);
+    })) {
+      context.error(str(exception));
+    }
+    context.exit();
+#if !KJ_NO_EXCEPTIONS
+  } catch (const TopLevelProcessContext::CleanShutdownException& e) {
+    return e.exitCode;
+  }
+#endif
+}
+
+// =======================================================================================
+
+struct MainBuilder::Impl {
+  inline Impl(ProcessContext& context, StringPtr version,
+              StringPtr briefDescription, StringPtr extendedDescription)
+      : context(context), version(version),
+        briefDescription(briefDescription), extendedDescription(extendedDescription) {}
+
+  ProcessContext& context;
+  StringPtr version;
+  StringPtr briefDescription;
+  StringPtr extendedDescription;
+
+  Arena arena;
+
+  struct CharArrayCompare {
+    inline bool operator()(const ArrayPtr<const char>& a, const ArrayPtr<const char>& b) const {
+      int cmp = memcmp(a.begin(), b.begin(), min(a.size(), b.size()));
+      if (cmp == 0) {
+        return a.size() < b.size();
+      } else {
+        return cmp < 0;
+      }
+    }
+  };
+
+  struct Option {
+    ArrayPtr<OptionName> names;
+    bool hasArg;
+    union {
+      Function<Validity()>* func;
+      Function<Validity(StringPtr)>* funcWithArg;
+    };
+    StringPtr argTitle;
+    StringPtr helpText;
+  };
+
+  class OptionDisplayOrder;
+
+  std::map<char, Option*> shortOptions;
+  std::map<ArrayPtr<const char>, Option*, CharArrayCompare> longOptions;
+
+  struct SubCommand {
+    Function<MainFunc()> func;
+    StringPtr helpText;
+  };
+  std::map<StringPtr, SubCommand> subCommands;
+
+  struct Arg {
+    StringPtr title;
+    Function<Validity(StringPtr)> callback;
+    uint minCount;
+    uint maxCount;
+  };
+
+  Vector<Arg> args;
+
+  Maybe<Function<Validity()>> finalCallback;
+
+  Option& addOption(std::initializer_list<OptionName> names, bool hasArg, StringPtr helpText) {
+    KJ_REQUIRE(names.size() > 0, "option must have at least one name");
+
+    Option& option = arena.allocate<Option>();
+    option.names = arena.allocateArray<OptionName>(names.size());
+    uint i = 0;
+    for (auto& name: names) {
+      option.names[i++] = name;
+      if (name.isLong) {
+        KJ_REQUIRE(
+            longOptions.insert(std::make_pair(StringPtr(name.longName).asArray(), &option)).second,
+            "duplicate option", name.longName);
+      } else {
+        KJ_REQUIRE(
+            shortOptions.insert(std::make_pair(name.shortName, &option)).second,
+            "duplicate option", name.shortName);
+      }
+    }
+    option.hasArg = hasArg;
+    option.helpText = helpText;
+    return option;
+  }
+
+  Validity printVersion() {
+    context.exitInfo(version);
+    return true;
+  }
+
+  Validity increaseVerbosity() {
+    context.increaseLoggingVerbosity();
+    return true;
+  }
+};
+
+MainBuilder::MainBuilder(ProcessContext& context, StringPtr version,
+                         StringPtr briefDescription, StringPtr extendedDescription)
+    : impl(heap<Impl>(context, version, briefDescription, extendedDescription)) {
+  addOption({"verbose"}, KJ_BIND_METHOD(*impl, increaseVerbosity),
+            "Log informational messages to stderr; useful for debugging.");
+  addOption({"version"}, KJ_BIND_METHOD(*impl, printVersion),
+            "Print version information and exit.");
+}
+
+MainBuilder::~MainBuilder() noexcept(false) {}
+
+MainBuilder& MainBuilder::addOption(std::initializer_list<OptionName> names,
+                                    Function<Validity()> callback,
+                                    StringPtr helpText) {
+  impl->addOption(names, false, helpText).func = &impl->arena.copy(kj::mv(callback));
+  return *this;
+}
+
+MainBuilder& MainBuilder::addOptionWithArg(std::initializer_list<OptionName> names,
+                                           Function<Validity(StringPtr)> callback,
+                                           StringPtr argumentTitle, StringPtr helpText) {
+  auto& opt = impl->addOption(names, true, helpText);
+  opt.funcWithArg = &impl->arena.copy(kj::mv(callback));
+  opt.argTitle = argumentTitle;
+  return *this;
+}
+
+MainBuilder& MainBuilder::addSubCommand(StringPtr name, Function<MainFunc()> getSubParser,
+                                        StringPtr helpText) {
+  KJ_REQUIRE(impl->args.size() == 0, "cannot have sub-commands when expecting arguments");
+  KJ_REQUIRE(impl->finalCallback == nullptr,
+             "cannot have a final callback when accepting sub-commands");
+  KJ_REQUIRE(
+      impl->subCommands.insert(std::make_pair(
+          name, Impl::SubCommand { kj::mv(getSubParser), helpText })).second,
+      "duplicate sub-command", name);
+  return *this;
+}
+
+MainBuilder& MainBuilder::expectArg(StringPtr title, Function<Validity(StringPtr)> callback) {
+  KJ_REQUIRE(impl->subCommands.empty(), "cannot have sub-commands when expecting arguments");
+  impl->args.add(Impl::Arg { title, kj::mv(callback), 1, 1 });
+  return *this;
+}
+MainBuilder& MainBuilder::expectOptionalArg(
+    StringPtr title, Function<Validity(StringPtr)> callback) {
+  KJ_REQUIRE(impl->subCommands.empty(), "cannot have sub-commands when expecting arguments");
+  impl->args.add(Impl::Arg { title, kj::mv(callback), 0, 1 });
+  return *this;
+}
+MainBuilder& MainBuilder::expectZeroOrMoreArgs(
+    StringPtr title, Function<Validity(StringPtr)> callback) {
+  KJ_REQUIRE(impl->subCommands.empty(), "cannot have sub-commands when expecting arguments");
+  impl->args.add(Impl::Arg { title, kj::mv(callback), 0, UINT_MAX });
+  return *this;
+}
+MainBuilder& MainBuilder::expectOneOrMoreArgs(
+    StringPtr title, Function<Validity(StringPtr)> callback) {
+  KJ_REQUIRE(impl->subCommands.empty(), "cannot have sub-commands when expecting arguments");
+  impl->args.add(Impl::Arg { title, kj::mv(callback), 1, UINT_MAX });
+  return *this;
+}
+
+MainBuilder& MainBuilder::callAfterParsing(Function<Validity()> callback) {
+  KJ_REQUIRE(impl->finalCallback == nullptr, "callAfterParsing() can only be called once");
+  KJ_REQUIRE(impl->subCommands.empty(), "cannot have a final callback when accepting sub-commands");
+  impl->finalCallback = kj::mv(callback);
+  return *this;
+}
+
+class MainBuilder::MainImpl {
+public:
+  MainImpl(Own<Impl>&& impl): impl(kj::mv(impl)) {}
+
+  void operator()(StringPtr programName, ArrayPtr<const StringPtr> params);
+
+private:
+  Own<Impl> impl;
+
+  void usageError(StringPtr programName, StringPtr message) KJ_NORETURN;
+  void printHelp(StringPtr programName) KJ_NORETURN;
+  void wrapText(Vector<char>& output, StringPtr indent, StringPtr text);
+};
+
+MainFunc MainBuilder::build() {
+  return MainImpl(kj::mv(impl));
+}
+
+void MainBuilder::MainImpl::operator()(StringPtr programName, ArrayPtr<const StringPtr> params) {
+  Vector<StringPtr> arguments;
+
+  for (size_t i = 0; i < params.size(); i++) {
+    StringPtr param = params[i];
+    if (param == "--") {
+      // "--" ends option parsing.
+      arguments.addAll(params.begin() + i + 1, params.end());
+      break;
+    } else if (param.startsWith("--")) {
+      // Long option.
+      ArrayPtr<const char> name;
+      Maybe<StringPtr> maybeArg;
+      KJ_IF_MAYBE(pos, param.findFirst('=')) {
+        name = param.slice(2, *pos);
+        maybeArg = param.slice(*pos + 1);
+      } else {
+        name = param.slice(2);
+      }
+      auto iter = impl->longOptions.find(name);
+      if (iter == impl->longOptions.end()) {
+        if (param == "--help") {
+          printHelp(programName);
+        } else {
+          usageError(programName, str("--", name, ": unrecognized option"));
+        }
+      } else {
+        const Impl::Option& option = *iter->second;
+        if (option.hasArg) {
+          // Argument expected.
+          KJ_IF_MAYBE(arg, maybeArg) {
+            // "--foo=blah": "blah" is the argument.
+            KJ_IF_MAYBE(error, (*option.funcWithArg)(*arg).releaseError()) {
+              usageError(programName, str(param, ": ", *error));
+            }
+          } else if (i + 1 < params.size() && !params[i + 1].startsWith("-")) {
+            // "--foo blah": "blah" is the argument.
+            ++i;
+            KJ_IF_MAYBE(error, (*option.funcWithArg)(params[i]).releaseError()) {
+              usageError(programName, str(param, "=", params[i], ": ", *error));
+            }
+          } else {
+            usageError(programName, str("--", name, ": missing argument"));
+          }
+        } else {
+          // No argument expected.
+          if (maybeArg == nullptr) {
+            KJ_IF_MAYBE(error, (*option.func)().releaseError()) {
+              usageError(programName, str(param, ": ", *error));
+            }
+          } else {
+            usageError(programName, str("--", name, ": option does not accept an argument"));
+          }
+        }
+      }
+    } else if (param.startsWith("-")) {
+      // Short option(s).
+      for (uint j = 1; j < param.size(); j++) {
+        char c = param[j];
+        auto iter = impl->shortOptions.find(c);
+        if (iter == impl->shortOptions.end()) {
+          usageError(programName, str("-", c, ": unrecognized option"));
+        } else {
+          const Impl::Option& option = *iter->second;
+          if (option.hasArg) {
+            // Argument expected.
+            if (j + 1 < params.size()) {
+              // Rest of flag is argument.
+              StringPtr arg = param.slice(j + 1);
+              KJ_IF_MAYBE(error, (*option.funcWithArg)(arg).releaseError()) {
+                usageError(programName, str("-", c, " ", arg, ": ", *error));
+              }
+              break;
+            } else if (i + 1 < params.size() && !params[i + 1].startsWith("-")) {
+              // Next parameter is argument.
+              ++i;
+              KJ_IF_MAYBE(error, (*option.funcWithArg)(params[i]).releaseError()) {
+                usageError(programName, str("-", c, " ", params[i], ": ", *error));
+              }
+              break;
+            } else {
+              usageError(programName, str("-", c, ": missing argument"));
+            }
+          } else {
+            // No argument expected.
+            KJ_IF_MAYBE(error, (*option.func)().releaseError()) {
+              usageError(programName, str("-", c, ": ", *error));
+            }
+          }
+        }
+      }
+    } else if (!impl->subCommands.empty()) {
+      // A sub-command name.
+      auto iter = impl->subCommands.find(param);
+      if (iter == impl->subCommands.end()) {
+        MainFunc subMain = iter->second.func();
+        subMain(str(programName, ' ', param), params.slice(i + 1, params.size()));
+        return;
+      } else if (param == "help") {
+        if (i + 1 < params.size()) {
+          iter = impl->subCommands.find(params[i + 1]);
+          if (iter == impl->subCommands.end()) {
+            usageError(programName, str(params[i + 1], ": unknown command"));
+          } else {
+            // Run the sub-command with "--help" as the argument.
+            MainFunc subMain = iter->second.func();
+            StringPtr dummyArg = "--help";
+            subMain(str(programName, ' ', params[i + 1]), arrayPtr(&dummyArg, 1));
+            return;
+          }
+        } else {
+          printHelp(programName);
+        }
+      } else {
+        // Arguments are not accepted, so this is an error.
+        usageError(programName, str(param, ": unknown command"));
+      }
+    } else {
+      // Just a regular argument.
+      arguments.add(param);
+    }
+  }
+
+  // ------------------------------------
+  // Handle arguments.
+  // ------------------------------------
+
+  // Count the number of required arguments, so that we know how to distribute the optional args.
+  uint requiredArgCount = 0;
+  for (auto& argSpec: impl->args) {
+    requiredArgCount += argSpec.minCount;
+  }
+
+  // Now go through each argument spec and consume arguments with it.
+  StringPtr* argPos = arguments.begin();
+  for (auto& argSpec: impl->args) {
+    uint i = 0;
+    for (; i < argSpec.minCount; i++) {
+      if (argPos == arguments.end()) {
+        usageError(programName, str("missing argument <", argSpec.title, '>'));
+      } else {
+        KJ_IF_MAYBE(error, argSpec.callback(*argPos).releaseError()) {
+          usageError(programName, str(*argPos, ": ", *error));
+        }
+        ++argPos;
+        --requiredArgCount;
+      }
+    }
+
+    // If we have more arguments than we need, and this argument spec will accept extras, give
+    // them to it.
+    for (; i < argSpec.maxCount && arguments.end() - argPos > requiredArgCount; ++i) {
+      KJ_IF_MAYBE(error, argSpec.callback(*argPos).releaseError()) {
+        usageError(programName, str(*argPos, ": ", *error));
+      }
+      ++argPos;
+    }
+  }
+
+  // Did we consume all the arguments?
+  while (argPos < arguments.end()) {
+    usageError(programName, str(*argPos++, ": too many arguments"));
+  }
+
+  // Run the final callback, if any.
+  KJ_IF_MAYBE(f, impl->finalCallback) {
+    KJ_IF_MAYBE(error, (*f)().releaseError()) {
+      usageError(programName, *error);
+    }
+  }
+}
+
+void MainBuilder::MainImpl::usageError(StringPtr programName, StringPtr message) {
+  impl->context.exitError(kj::str(
+      programName, ": ", message,
+      "\nTry '", programName, " --help' for more information."));
+}
+
+class MainBuilder::Impl::OptionDisplayOrder {
+public:
+  bool operator()(const Option* a, const Option* b) {
+    if (a == b) return false;
+
+    char aShort = '\0';
+    char bShort = '\0';
+
+    for (auto& name: a->names) {
+      if (name.isLong) {
+        if (aShort == '\0') {
+          aShort = name.longName[0];
+        }
+      } else {
+        aShort = name.shortName;
+        break;
+      }
+    }
+    for (auto& name: b->names) {
+      if (name.isLong) {
+        if (bShort == '\0') {
+          bShort = name.longName[0];
+        }
+      } else {
+        bShort = name.shortName;
+        break;
+      }
+    }
+
+    if (aShort < bShort) return true;
+    if (aShort > bShort) return false;
+
+    StringPtr aLong;
+    StringPtr bLong;
+
+    for (auto& name: a->names) {
+      if (name.isLong) {
+        aLong = name.longName;
+        break;
+      }
+    }
+    for (auto& name: b->names) {
+      if (name.isLong) {
+        bLong = name.longName;
+        break;
+      }
+    }
+
+    return aLong < bLong;
+  }
+};
+
+void MainBuilder::MainImpl::printHelp(StringPtr programName) {
+  Vector<char> text(1024);
+
+  std::set<const Impl::Option*, Impl::OptionDisplayOrder> sortedOptions;
+
+  for (auto& entry: impl->shortOptions) {
+    sortedOptions.insert(entry.second);
+  }
+  for (auto& entry: impl->longOptions) {
+    sortedOptions.insert(entry.second);
+  }
+
+  text.addAll(str("Usage: ", programName, sortedOptions.empty() ? "" : " [<option>...]"));
+
+  if (impl->subCommands.empty()) {
+    for (auto& arg: impl->args) {
+      text.add(' ');
+      if (arg.minCount == 0) {
+        text.addAll(str("[<", arg.title, arg.maxCount > 1 ? ">...]" : ">]"));
+      } else {
+        text.addAll(str('<', arg.title, arg.maxCount > 1 ? ">..." : ">"));
+      }
+    }
+  } else {
+    text.addAll(StringPtr(" <command> [<arg>...]"));
+  }
+  text.addAll(StringPtr("\n\n"));
+
+  wrapText(text, "", impl->briefDescription);
+
+  if (!impl->subCommands.empty()) {
+    text.addAll(StringPtr("\nCommands:\n"));
+    size_t maxLen = 0;
+    for (auto& command: impl->subCommands) {
+      maxLen = kj::max(maxLen, command.first.size());
+    }
+    for (auto& command: impl->subCommands) {
+      text.addAll(StringPtr("  "));
+      text.addAll(command.first);
+      for (size_t i = command.first.size(); i < maxLen; i++) {
+        text.add(' ');
+      }
+      text.addAll(StringPtr("  "));
+      text.addAll(command.second.helpText);
+      text.add('\n');
+    }
+    text.addAll(str(
+        "\nSee '", programName, " help <command>' for more information on a specific command.\n"));
+  }
+
+  if (!sortedOptions.empty()) {
+    text.addAll(StringPtr("\nOptions:\n"));
+
+    for (auto opt: sortedOptions) {
+      text.addAll(StringPtr("    "));
+      bool isFirst = true;
+      for (auto& name: opt->names) {
+        if (isFirst) {
+          isFirst = false;
+        } else {
+          text.addAll(StringPtr(", "));
+        }
+        if (name.isLong) {
+          text.addAll(str("--", name.longName));
+          if (opt->hasArg) {
+            text.addAll(str("=<", opt->argTitle, '>'));
+          }
+        } else {
+          text.addAll(str("-", name.shortName));
+          if (opt->hasArg) {
+            text.addAll(str('<', opt->argTitle, '>'));
+          }
+        }
+      }
+      text.add('\n');
+      wrapText(text, "        ", opt->helpText);
+    }
+
+    text.addAll(StringPtr("    --help\n        Display this help text and exit.\n"));
+  }
+
+  if (impl->extendedDescription.size() > 0) {
+    text.add('\n');
+    wrapText(text, "", impl->extendedDescription);
+  }
+
+  text.add('\0');
+  impl->context.exitInfo(String(text.releaseAsArray()));
+}
+
+void MainBuilder::MainImpl::wrapText(Vector<char>& output, StringPtr indent, StringPtr text) {
+  uint width = 80 - indent.size();
+
+  while (text.size() > 0) {
+    output.addAll(indent);
+
+    KJ_IF_MAYBE(lineEnd, text.findFirst('\n')) {
+      if (*lineEnd <= width) {
+        output.addAll(text.slice(0, *lineEnd + 1));
+        text = text.slice(*lineEnd + 1);
+        continue;
+      }
+    }
+
+    if (text.size() <= width) {
+      output.addAll(text);
+      output.add('\n');
+      break;
+    }
+
+    uint wrapPos = width;
+    for (;; wrapPos--) {
+      if (wrapPos == 0) {
+        // Hmm, no good place to break words.  Just break in the middle.
+        wrapPos = width;
+        break;
+      } else if (text[wrapPos] == ' ' && text[wrapPos - 1] != ' ') {
+        // This position is a space and is preceded by a non-space.  Wrap here.
+        break;
+      }
+    }
+
+    output.addAll(text.slice(0, wrapPos));
+    output.add('\n');
+
+    // Skip spaces after the text that was printed.
+    while (text[wrapPos] == ' ') {
+      ++wrapPos;
+    }
+    if (text[wrapPos] == '\n') {
+      // Huh, apparently there were a whole bunch of spaces at the end of the line followed by a
+      // newline.  Skip the newline as well so we don't print a blank line.
+      ++wrapPos;
+    }
+    text = text.slice(wrapPos);
+  }
+}
+
+}  // namespace kj
diff --git a/c++/src/kj/main.h b/c++/src/kj/main.h
new file mode 100644
index 0000000..2702b14
--- /dev/null
+++ b/c++/src/kj/main.h
@@ -0,0 +1,346 @@
+// Copyright (c) 2013, Kenton Varda <temporal@gmail.com>
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this
+//    list of conditions and the following disclaimer.
+// 2. Redistributions in binary form must reproduce the above copyright notice,
+//    this list of conditions and the following disclaimer in the documentation
+//    and/or other materials provided with the distribution.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+// ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+// (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+// LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+// ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef KJ_MAIN_H_
+#define KJ_MAIN_H_
+
+#include "array.h"
+#include "string.h"
+#include "vector.h"
+#include "function.h"
+
+namespace kj {
+
+class ProcessContext {
+  // Context for command-line programs.
+
+public:
+  virtual StringPtr getProgramName() = 0;
+  // Get argv[0] as passed to main().
+
+  virtual void exit() KJ_NORETURN = 0;
+  // Indicates program completion.  The program is considered successful unless `error()` was
+  // called.  Typically this exits with quick_exit(), meaning that the stack is not unwound, buffers
+  // are not flushed, etc. -- it is the responsibility of the caller to flush any buffers that
+  // matter.  However, an alternate context implementation e.g. for unit testing purposes could
+  // choose to throw an exception instead.
+
+  virtual void warning(StringPtr message) = 0;
+  // Print the given message to standard error.  A newline is printed after the message if it
+  // doesn't already have one.
+
+  virtual void error(StringPtr message) = 0;
+  // Like `warning()`, but also sets a flag indicating that the process has failed, and that when
+  // it eventually exits it should indicate an error status.
+
+  virtual void exitError(StringPtr message) KJ_NORETURN = 0;
+  // Equivalent to `error(message)` followed by `exit()`.
+
+  virtual void exitInfo(StringPtr message) KJ_NORETURN = 0;
+  // Displays the given non-error message to the user and then calls `exit()`.  This is used to
+  // implement things like --help.
+
+  virtual void increaseLoggingVerbosity() = 0;
+  // Increase the level of detail produced by the debug logging system.  `MainBuilder` invokes
+  // this if the caller uses the -v flag.
+
+  // TODO(someday):  Add interfaces representing standard OS resources like the filesystem, so that
+  //   these things can be mocked out.
+};
+
+class TopLevelProcessContext final: public ProcessContext {
+  // A ProcessContext implementation appropriate for use at the actual entry point of a process
+  // (as opposed to when you are trying to call a program's main function from within some other
+  // program).  This implementation writes errors to stderr, and its `exit()` method actually
+  // calls the C `quick_exit()` function.
+
+public:
+  explicit TopLevelProcessContext(StringPtr programName);
+
+  struct CleanShutdownException { int exitCode; };
+  // If the environment variable KJ_CLEAN_SHUTDOWN is set, then exit() will actually throw this
+  // exception rather than exiting.  `kj::runMain()` catches this exception and returns normally.
+  // This is useful primarily for testing purposes, to assist tools like memory leak checkers that
+  // are easily confused by quick_exit().
+
+  StringPtr getProgramName() override;
+  void exit() KJ_NORETURN override;
+  void warning(StringPtr message) override;
+  void error(StringPtr message) override;
+  void exitError(StringPtr message) KJ_NORETURN override;
+  void exitInfo(StringPtr message) KJ_NORETURN override;
+  void increaseLoggingVerbosity() override;
+
+private:
+  StringPtr programName;
+  bool cleanShutdown;
+  bool hadErrors = false;
+};
+
+typedef Function<void(StringPtr programName, ArrayPtr<const StringPtr> params)> MainFunc;
+
+int runMainAndExit(ProcessContext& context, MainFunc&& func, int argc, char* argv[]);
+// Runs the given main function and then exits using the given context.  If an exception is thrown,
+// this will catch it, report it via the context and exit with an error code.
+//
+// Normally this function does not return, because returning would probably lead to wasting time
+// on cleanup when the process is just going to exit anyway.  However, to facilitate memory leak
+// checkers and other tools that require a clean shutdown to do their job, if the environment
+// variable KJ_CLEAN_SHUTDOWN is set, the function will in fact return an exit code, which should
+// then be returned from main().
+//
+// Most users will use the KJ_MAIN() macro rather than call this function directly.
+
+#define KJ_MAIN(MainClass) \
+  int main(int argc, char* argv[]) { \
+    ::kj::TopLevelProcessContext context(argv[0]); \
+    MainClass mainObject(context); \
+    return ::kj::runMainAndExit(context, mainObject.getMain(), argc, argv); \
+  }
+// Convenience macro for declaring a main function based on the given class.  The class must have
+// a constructor that accepts a ProcessContext& and a method getMain() which returns
+// kj::MainFunc (probably building it using a MainBuilder).
+
+class MainBuilder {
+  // Builds a main() function with nice argument parsing.  As options and arguments are parsed,
+  // corresponding callbacks are called, so that you never have to write a massive switch()
+  // statement to interpret arguments.  Additionally, this approach encourages you to write
+  // main classes that have a reasonable API that can be used as an alternative to their
+  // command-line interface.
+  //
+  // All StringPtrs passed to MainBuilder must remain valid until option parsing completes.  The
+  // assumption is that these strings will all be literals, making this an easy requirement.  If
+  // not, consider allocating them in an Arena.
+  //
+  // Some flags are automatically recognized by the main functions built by this class:
+  //     --help:  Prints help text and exits.  The help text is constructed based on the
+  //       information you provide to the builder as you define each flag.
+  //     --verbose:  Increase logging verbosity.
+  //     --version:  Print version information and exit.
+  //
+  // Example usage:
+  //
+  //     class FooMain {
+  //     public:
+  //       FooMain(kj::ProcessContext& context): context(context) {}
+  //
+  //       bool setAll() { all = true; return true; }
+  //       // Enable the --all flag.
+  //
+  //       kj::MainBuilder::Validity setOutput(kj::StringPtr name) {
+  //         // Set the output file.
+  //
+  //         if (name.endsWith(".foo")) {
+  //           outputFile = name;
+  //           return true;
+  //         } else {
+  //           return "Output file must have extension .foo.";
+  //         }
+  //       }
+  //
+  //       kj::MainBuilder::Validity processInput(kj::StringPtr name) {
+  //         // Process an input file.
+  //
+  //         if (!exists(name)) {
+  //           return kj::str(name, ": file not found");
+  //         }
+  //         // ... process the input file ...
+  //         return true;
+  //       }
+  //
+  //       kj::MainFunc getMain() {
+  //         return MainBuilder(context, "Foo Builder v1.5", "Reads <source>s and builds a Foo.")
+  //             .addOption({'a', "all"}, KJ_BIND_METHOD(*this, setAll),
+  //                 "Frob all the widgets.  Otherwise, only some widgets are frobbed.")
+  //             .addOptionWithArg({'o', "output"}, KJ_BIND_METHOD(*this, setOutput),
+  //                 "filename", "Output to <filename>.  Must be a .foo file.")
+  //             .expectOneOrMoreArgs("source", KJ_BIND_METHOD(*this, processInput))
+  //             .build();
+  //       }
+  //
+  //     private:
+  //       bool all = false;
+  //       kj::StringPtr outputFile;
+  //       kj::ProcessContext& context;
+  //     };
+
+public:
+  MainBuilder(ProcessContext& context, StringPtr version,
+              StringPtr briefDescription, StringPtr extendedDescription = nullptr);
+  ~MainBuilder() noexcept(false);
+
+  class OptionName {
+  public:
+    OptionName() = default;
+    inline constexpr OptionName(char shortName): isLong(false), shortName(shortName) {}
+    inline constexpr OptionName(const char* longName): isLong(true), longName(longName) {}
+
+  private:
+    bool isLong;
+    union {
+      char shortName;
+      const char* longName;
+    };
+    friend class MainBuilder;
+  };
+
+  class Validity {
+  public:
+    inline Validity(bool valid) {
+      if (!valid) errorMessage = heapString("invalid argument");
+    }
+    inline Validity(const char* errorMessage)
+        : errorMessage(heapString(errorMessage)) {}
+    inline Validity(String&& errorMessage)
+        : errorMessage(kj::mv(errorMessage)) {}
+
+    inline const Maybe<String>& getError() const { return errorMessage; }
+    inline Maybe<String> releaseError() { return kj::mv(errorMessage); }
+
+  private:
+    Maybe<String> errorMessage;
+    friend class MainBuilder;
+  };
+
+  MainBuilder& addOption(std::initializer_list<OptionName> names, Function<Validity()> callback,
+                         StringPtr helpText);
+  // Defines a new option (flag).  `names` is a list of characters and strings that can be used to
+  // specify the option on the command line.  Single-character names are used with "-" while string
+  // names are used with "--".  `helpText` is a natural-language description of the flag.
+  //
+  // `callback` is called when the option is seen.  Its return value indicates whether the option
+  // was accepted.  If not, further option processing stops, and error is written, and the process
+  // exits.
+  //
+  // Example:
+  //
+  //     builder.addOption({'a', "all"}, KJ_BIND_METHOD(*this, showAll), "Show all files.");
+  //
+  // This option could be specified in the following ways:
+  //
+  //     -a
+  //     --all
+  //
+  // Note that single-character option names can be combined into a single argument.  For example,
+  // `-abcd` is equivalent to `-a -b -c -d`.
+  //
+  // The help text for this option would look like:
+  //
+  //     -a, --all
+  //         Show all files.
+  //
+  // Note that help text is automatically word-wrapped.
+
+  MainBuilder& addOptionWithArg(std::initializer_list<OptionName> names,
+                                Function<Validity(StringPtr)> callback,
+                                StringPtr argumentTitle, StringPtr helpText);
+  // Like `addOption()`, but adds an option which accepts an argument.  `argumentTitle` is used in
+  // the help text.  The argument text is passed to the callback.
+  //
+  // Example:
+  //
+  //     builder.addOptionWithArg({'o', "output"}, KJ_BIND_METHOD(*this, setOutput),
+  //                              "filename", "Output to <filename>.");
+  //
+  // This option could be specified with an argument of "foo" in the following ways:
+  //
+  //     -ofoo
+  //     -o foo
+  //     --output=foo
+  //     --output foo
+  //
+  // Note that single-character option names can be combined, but only the last option can have an
+  // argument, since the characters after the option letter are interpreted as the argument.  E.g.
+  // `-abofoo` would be equivalent to `-a -b -o foo`.
+  //
+  // The help text for this option would look like:
+  //
+  //     -o FILENAME, --output=FILENAME
+  //         Output to FILENAME.
+
+  MainBuilder& addSubCommand(StringPtr name, Function<MainFunc()> getSubParser,
+                             StringPtr briefHelpText);
+  // If exactly the given name is seen as an argument, invoke getSubParser() and then pass all
+  // remaining arguments to the parser it returns.  This is useful for implementing commands which
+  // have lots of sub-commands, like "git" (which has sub-commands "checkout", "branch", "pull",
+  // etc.).
+  //
+  // `getSubParser` is only called if the command is seen.  This avoids building main functions
+  // for commands that aren't used.
+  //
+  // `briefHelpText` should be brief enough to show immediately after the command name on a single
+  // line.  It will not be wrapped.  Users can use the built-in "help" command to get extended
+  // help on a particular command.
+
+  MainBuilder& expectArg(StringPtr title, Function<Validity(StringPtr)> callback);
+  MainBuilder& expectOptionalArg(StringPtr title, Function<Validity(StringPtr)> callback);
+  MainBuilder& expectZeroOrMoreArgs(StringPtr title, Function<Validity(StringPtr)> callback);
+  MainBuilder& expectOneOrMoreArgs(StringPtr title, Function<Validity(StringPtr)> callback);
+  // Set callbacks to handle arguments.  `expectArg()` and `expectOptionalArg()` specify positional
+  // arguments with special handling, while `expect{Zero,One}OrMoreArgs()` specifies a handler for
+  // an argument list (the handler is called once for each argument in the list).  `title`
+  // specifies how the argument should be represented in the usage text.
+  //
+  // All options callbacks are called before argument callbacks, regardless of their ordering on
+  // the command line.  This matches GNU getopt's behavior of permuting non-flag arguments to the
+  // end of the argument list.  Also matching getopt, the special option "--" indicates that the
+  // rest of the command line is all arguments, not options, even if they start with '-'.
+  //
+  // The interpretation of positional arguments is fairly flexible.  The non-optional arguments can
+  // be expected at the beginning, end, or in the middle.  If more arguments are specified than
+  // the number of non-optional args, they are assigned to the optional argument handlers in the
+  // order of registration.
+  //
+  // For example, say you called:
+  //     builder.expectArg("foo", ...);
+  //     builder.expectOptionalArg("bar", ...);
+  //     builder.expectArg("baz", ...);
+  //     builder.expectZeroOrMoreArgs("qux", ...);
+  //     builder.expectArg("corge", ...);
+  //
+  // This command requires at least three arguments: foo, baz, and corge.  If four arguments are
+  // given, the second is assigned to bar.  If five or more arguments are specified, then the
+  // arguments between the third and last are assigned to qux.  Note that it never makes sense
+  // to call `expect*OrMoreArgs()` more than once since only the first call would ever be used.
+  //
+  // In practice, you probably shouldn't create such complicated commands as in the above example.
+  // But, this flexibility seems necessary to support commands where the first argument is special
+  // as well as commands (like `cp`) where the last argument is special.
+
+  MainBuilder& callAfterParsing(Function<Validity()> callback);
+  // Call the given function after all arguments have been parsed.
+
+  MainFunc build();
+  // Build the "main" function, which simply parses the arguments.  Once this returns, the
+  // `MainBuilder` is no longer valid.
+
+private:
+  struct Impl;
+  Own<Impl> impl;
+
+  class MainImpl;
+};
+
+}  // namespace kj
+
+#endif  // KJ_MAIN_H_
diff --git a/c++/src/kj/string.h b/c++/src/kj/string.h
index 33b8f40..baf7502 100644
--- a/c++/src/kj/string.h
+++ b/c++/src/kj/string.h
@@ -84,6 +84,8 @@
   inline bool startsWith(const StringPtr& other) const;
   inline bool endsWith(const StringPtr& other) const;
 
+  inline Maybe<size_t> findFirst(char c) const;
+
 private:
   inline StringPtr(ArrayPtr<const char> content): content(content) {}
 
@@ -109,6 +111,8 @@
   inline String(decltype(nullptr)): content(nullptr) {}
   inline String(char* value, size_t size, const ArrayDisposer& disposer);
   // Does not copy.  `size` does not include NUL terminator, but `value` must be NUL-terminated.
+  inline explicit String(Array<char> buffer);
+  // Does not copy.  Requires `buffer` ends with `\0`.
 
   inline operator ArrayPtr<char>();
   inline operator ArrayPtr<const char>() const;
@@ -373,6 +377,15 @@
       memcmp(end() - other.size(), other.content.begin(), other.size()) == 0;
 }
 
+inline Maybe<size_t> StringPtr::findFirst(char c) const {
+  const char* pos = reinterpret_cast<const char*>(memchr(content.begin(), c, size()));
+  if (pos == nullptr) {
+    return nullptr;
+  } else {
+    return pos - content.begin();
+  }
+}
+
 inline String::operator ArrayPtr<char>() {
   return content == nullptr ? ArrayPtr<char>(nullptr) : content.slice(0, content.size() - 1);
 }
@@ -404,6 +417,10 @@
   KJ_IREQUIRE(value[size] == '\0', "String must be NUL-terminated.");
 }
 
+inline String::String(Array<char> buffer): content(kj::mv(buffer)) {
+  KJ_IREQUIRE(content.size() > 0 && content.back() == '\0', "String must be NUL-terminated.");
+}
+
 inline String heapString(const char* value) {
   return heapString(value, strlen(value));
 }
diff --git a/c++/src/kj/vector.h b/c++/src/kj/vector.h
index 76549a9..3f7db56 100644
--- a/c++/src/kj/vector.h
+++ b/c++/src/kj/vector.h
@@ -82,6 +82,11 @@
     builder.addAll(begin, end);
   }
 
+  template <typename Container>
+  inline void addAll(Container&& container) {
+    addAll(container.begin(), container.end());
+  }
+
 private:
   ArrayBuilder<T> builder;