diff --git a/CMakeLists.txt b/CMakeLists.txt
index 242958f..6bb67df 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -23,6 +23,7 @@ target_sources(vm_lib
   src/fio.cpp
   src/stdlib.cpp
   src/lineedit.cpp
+  src/serialize.cpp
 
   PUBLIC
   FILE_SET HEADERS
@@ -43,6 +44,7 @@ target_sources(vm_lib
   src/fio.hpp
   src/stdlib.hpp
   src/lineedit.hpp
+  src/serialize.hpp
 )
 
 add_executable(valeri src/valeri.cpp)
@@ -67,6 +69,8 @@ set(LISP_TESTS
   dict
   function
   collections
+  continuations
+  serialize
 )
 
 
diff --git a/src/arena.cpp b/src/arena.cpp
index ab0853c..f027c09 100644
--- a/src/arena.cpp
+++ b/src/arena.cpp
@@ -265,6 +265,7 @@ Result<PodObject*> Arena::gc_stack(PodStackFrame* obj) {
   nobj->header.tag = Tag::StackFrame;
   nobj->parent = TRY(gc_pod(obj->parent.get()));
   nobj->fun = TRY(gc_pod(obj->fun.get()));
+  nobj->guard = obj->guard;
   nobj->pc = obj->pc;
   nobj->size = obj->size;
   for (uint64_t i = 0; i < obj->size; i++) {
diff --git a/src/arena.hpp b/src/arena.hpp
index fe012f3..f77d38e 100644
--- a/src/arena.hpp
+++ b/src/arena.hpp
@@ -16,6 +16,10 @@ class GcRootList;
 Arena& get_arena();
 void set_arena(Arena& arena);
 
+static uint64_t round_up(uint64_t number, uint64_t to) {
+  return ((number + to - 1) / to) * to;
+}
+
 class GcRootBase {
  public:
   friend class Arena;
@@ -131,11 +135,29 @@ class Arena {
     uint64_t objsize = sizeof(T) + extra;
     auto ptr = _first->alloc(objsize);
 
-    if (ptr.has_value()) return (T*)ptr.value();
+    if (ptr.has_value()) {
+      new (ptr.value()) T();
+      return (T*)ptr.value();
+    }
 
-    // TODO: trigger GC
+    TRY(gc());
 
-    return (T*)TRY(_first->alloc(objsize));
+    T* res = (T*)TRY(_first->alloc(objsize));
+    new (res) T();
+    return res;
+  }
+
+  template <class T>
+  Result<T*> alloc_bytes(uint64_t size = 0) {
+    auto ptr = _first->alloc(size);
+
+    if (ptr.has_value()) {
+      return (T*)ptr.value();
+    }
+
+    TRY(gc());
+
+    return (T*)TRY(_first->alloc(size));
   }
 
   Result<void> gc();
@@ -205,6 +227,11 @@ Result<T*> arena_alloc(uint64_t extra = 0) {
   return get_arena().alloc<T>(extra);
 }
 
+template <class T>
+Result<T*> arena_alloc_bytes(uint64_t size = 0) {
+  return get_arena().alloc_bytes<T>(size);
+}
+
 Result<void> arena_gc();
 
 template <class T>
diff --git a/src/common.cpp b/src/common.cpp
index 15c5425..b40fedf 100644
--- a/src/common.cpp
+++ b/src/common.cpp
@@ -61,7 +61,6 @@ Result<Symbol> Symbol::create(String& rhs) {
   uint64_t res_size = rhs_size;
 
   auto pod = TRY(arena_alloc<PodSymbol>(res_size * sizeof(char32_t)));
-  pod->header.tag = Tag::Symbol;
   pod->size = res_size;
   memcpy(pod->data, rhs._value->data, sizeof(char32_t) * rhs_size);
 
@@ -73,7 +72,6 @@ Result<String> String::create(const Symbol& rhs) {
   uint64_t res_size = rhs_size;
 
   auto pod = TRY(arena_alloc<PodString>(res_size * sizeof(char32_t)));
-  pod->header.tag = Tag::String;
   pod->size = res_size;
   memcpy(pod->data, rhs._value->data, sizeof(char32_t) * rhs_size);
 
@@ -87,7 +85,6 @@ Result<ByteArray> ByteArray::create(const String& str) {
     size += utf8_codepoint_size(TRY(str[i]));
   }
   auto pod = TRY(arena_alloc<PodByteArray>(size * sizeof(char)));
-  pod->header.tag = Tag::ByteArray;
   pod->size = size;
 
   char* res = pod->data;
@@ -100,9 +97,106 @@ Result<ByteArray> ByteArray::create(const String& str) {
   return ByteArray(TRY(MkGcRoot(pod)));
 }
 
+Result<String> ByteArray::hex() const {
+  auto size = _value->size * 2;
+  auto pod = TRY(arena_alloc<PodString>(size * sizeof(char32_t)));
+  pod->size = size;
+
+  const char* hexa = "0123456789ABCDEF";
+  for (uint64_t i = 0; i < _value->size; i++) {
+    auto b = (uint8_t)_value->data[i];
+    pod->data[i * 2] = hexa[(b >> 4) & 0xF];
+    pod->data[i * 2 + 1] = hexa[b & 0xF];
+  }
+
+  return String(TRY(MkGcRoot(pod)));
+}
+Result<ByteArray> ByteArray::to_rle() const {
+  auto size = _value->size;
+
+  auto compressed_size = 0;
+  for (uint64_t i = 0; i < size; ++i) {
+    auto b = _value->data[i];
+    if (b == 0) {
+      uint64_t rl = 0;
+      for (uint64_t j = 0; j < 255 && i + j < size && _value->data[i + j] == 0;
+           j++) {
+        rl++;
+      }
+      i += rl - 1;
+      compressed_size += 2;
+    } else {
+      ++compressed_size;
+    }
+  }
+
+  auto pod = TRY(arena_alloc<PodByteArray>(compressed_size));
+  pod->size = compressed_size;
+
+  auto pos = 0;
+  for (uint64_t i = 0; i < size; ++i) {
+    auto b = _value->data[i];
+    if (b == 0) {
+      uint64_t rl = 0;
+      for (uint64_t j = 0; j < 255 && i + j < size && _value->data[i + j] == 0;
+           j++) {
+        rl++;
+      }
+      i += rl - 1;
+      pod->data[pos] = 0;
+      pod->data[pos + 1] = rl;
+      pos += 2;
+    } else {
+      pod->data[pos] = _value->data[i];
+      ++pos;
+    }
+  }
+
+  return ByteArray(TRY(MkGcRoot(pod)));
+}
+
+Result<ByteArray> ByteArray::from_rle() const {
+  uint64_t size = _value->size;
+  uint64_t decompressed_size = 0;
+
+  for (uint64_t i = 0; i < size; ++i) {
+    auto b = _value->data[i];
+    if (b == 0) {
+      if (i + 1 >= size) {
+        return ERROR(KeyError);
+      }
+      decompressed_size += _value->data[i + 1];
+      i += 1;
+    } else {
+      ++decompressed_size;
+    }
+  }
+
+  auto pod = TRY(arena_alloc<PodByteArray>(decompressed_size));
+  pod->size = decompressed_size;
+
+  uint64_t pos = 0;
+  for (uint64_t i = 0; i < size; ++i) {
+    auto b = _value->data[i];
+    if (b == 0) {
+      uint64_t run_size = _value->data[i + 1];
+
+      for (uint64_t j = 0; j < run_size; j++) {
+        pod->data[pos + j] = 0;
+      }
+      i += 1;
+      pos += run_size;
+    } else {
+      pod->data[pos] = _value->data[i];
+      ++pos;
+    }
+  }
+
+  return ByteArray(TRY(MkGcRoot(pod)));
+}
+
 Result<SrcLoc> SrcLoc::create(const SourceRange& sourcerange) {
   auto pod = TRY(arena_alloc<PodSrcLoc>());
-  pod->header.tag = Tag::SrcLoc;
   pod->sourcerange = sourcerange;
 
   return SrcLoc(TRY(MkGcRoot(pod)));
@@ -134,7 +228,6 @@ Result<short> SrcLoc::cmp(const SrcLoc& rhs) const {
 Result<Syntax> Syntax::create(const String& filename, const SrcLoc& srcloc,
                               const Value& expression) {
   auto pod = TRY(arena_alloc<PodSyntax>());
-  pod->header.tag = Tag::Syntax;
   pod->filename = filename.pod();
   pod->srcloc = srcloc.pod();
   pod->expression = expression.pod();
@@ -342,12 +435,13 @@ Result<short> Module::cmp(const Module& rhs) const {
   return res;
 }
 
-Result<StackFrame> StackFrame::create(const Value& parent, const Value& fun) {
+Result<StackFrame> StackFrame::create(const Value& parent, const Value& fun,
+                                      bool guard) {
   auto pod = TRY(arena_alloc<PodStackFrame>());
-  pod->header.tag = Tag::StackFrame;
 
   pod->parent = parent.pod();
   pod->fun = fun.pod();
+  pod->guard = guard;
   pod->pc = 0;
   pod->size = 0;
 
@@ -371,11 +465,11 @@ Result<Value> StackFrame::get(uint64_t idx) const {
 Result<StackFrame> StackFrame::set(uint64_t idx, const Value& val) const {
   uint64_t size = std::max(_value->size, idx + 1);
   auto pod = TRY(arena_alloc<PodStackFrame>(sizeof(OffPtr<PodObject>) * size));
-  pod->header.tag = Tag::StackFrame;
 
   pod->parent = _value->parent;
   pod->fun = _value->fun;
   pod->pc = _value->pc;
+  pod->guard = _value->guard;
   pod->size = size;
 
   for (uint64_t i = 0; i < _value->size; i++) {
@@ -394,10 +488,10 @@ Result<StackFrame> StackFrame::set(uint64_t idx, const Value& val) const {
 
 Result<StackFrame> StackFrame::settop(uint64_t idx) const {
   auto pod = TRY(arena_alloc<PodStackFrame>(sizeof(OffPtr<PodObject>) * idx));
-  pod->header.tag = Tag::StackFrame;
 
   pod->parent = _value->parent;
   pod->fun = _value->fun;
+  pod->guard = _value->guard;
   pod->pc = _value->pc;
   pod->size = idx;
 
@@ -427,10 +521,10 @@ uint64_t StackFrame::pc() const { return _value->pc; }
 Result<StackFrame> StackFrame::setpc(uint64_t pc) {
   auto pod =
       TRY(arena_alloc<PodStackFrame>(sizeof(OffPtr<PodObject>) * _value->size));
-  pod->header.tag = Tag::StackFrame;
 
   pod->parent = _value->parent;
   pod->fun = _value->fun;
+  pod->guard = _value->guard;
   pod->pc = pc;
   pod->size = _value->size;
 
@@ -476,6 +570,105 @@ Result<StackFrame> StackFrame::ret(uint64_t regnum) const {
   return std::move(parent_stack);
 }
 
+Result<StackFrame> StackFrame::detach(uint64_t depth) const {
+  if (depth == 0) {
+    uint64_t size = _value->size;
+    auto pod =
+        TRY(arena_alloc<PodStackFrame>(sizeof(OffPtr<PodObject>) * size));
+
+    pod->parent = TRY(Nil::create()).pod();
+    pod->fun = _value->fun;
+    pod->guard = _value->guard;
+    pod->pc = _value->pc;
+    pod->size = size;
+
+    for (uint64_t i = 0; i < _value->size; i++) {
+      pod->data[i] = _value->data[i];
+    }
+
+    return StackFrame(TRY(MkGcRoot(pod)));
+  }
+
+  auto par = TRY(parent());
+  if (par.is<Nil>()) return ERROR(KeyError);
+
+  StackFrame& par_frame = *par.to<StackFrame>();
+
+  auto par_frame_new = TRY(par_frame.detach(depth - 1));
+
+  uint64_t size = _value->size;
+  auto pod = TRY(arena_alloc<PodStackFrame>(sizeof(OffPtr<PodObject>) * size));
+
+  pod->parent = par_frame_new.pod();
+  pod->fun = _value->fun;
+  pod->guard = _value->guard;
+  pod->pc = _value->pc;
+  pod->size = size;
+
+  for (uint64_t i = 0; i < _value->size; i++) {
+    pod->data[i] = _value->data[i];
+  }
+
+  return StackFrame(TRY(MkGcRoot(pod)));
+}
+
+Result<StackFrame> StackFrame::attach(const StackFrame& frame) const {
+  auto par = TRY(parent());
+  if (par.is<Nil>()) {
+    uint64_t size = _value->size;
+    auto pod =
+        TRY(arena_alloc<PodStackFrame>(sizeof(OffPtr<PodObject>) * size));
+
+    pod->parent = frame.pod();
+    pod->fun = _value->fun;
+    pod->guard = _value->guard;
+    pod->pc = _value->pc;
+    pod->size = size;
+
+    for (uint64_t i = 0; i < _value->size; i++) {
+      pod->data[i] = _value->data[i];
+    }
+
+    return StackFrame(TRY(MkGcRoot(pod)));
+  }
+
+  StackFrame& par_frame = *par.to<StackFrame>();
+
+  auto par_frame_new = TRY(par_frame.attach(frame));
+
+  uint64_t size = _value->size;
+  auto pod = TRY(arena_alloc<PodStackFrame>(sizeof(OffPtr<PodObject>) * size));
+
+  pod->parent = par_frame_new.pod();
+  pod->fun = _value->fun;
+  pod->guard = _value->guard;
+  pod->pc = _value->pc;
+  pod->size = size;
+
+  for (uint64_t i = 0; i < _value->size; i++) {
+    pod->data[i] = _value->data[i];
+  }
+
+  return StackFrame(TRY(MkGcRoot(pod)));
+}
+
+Result<StackFrame> StackFrame::set_guard(bool guard) const {
+  uint64_t size = _value->size;
+  auto pod = TRY(arena_alloc<PodStackFrame>(sizeof(OffPtr<PodObject>) * size));
+
+  pod->parent = _value->parent;
+  pod->fun = _value->fun;
+  pod->guard = guard;
+  pod->pc = _value->pc;
+  pod->size = size;
+
+  for (uint64_t i = 0; i < _value->size; i++) {
+    pod->data[i] = _value->data[i];
+  }
+
+  return StackFrame(TRY(MkGcRoot(pod)));
+}
+
 Result<String> StackFrame::backtrace(uint64_t indent) const {
   String res = TRY(String::create(""));
 
@@ -483,34 +676,36 @@ Result<String> StackFrame::backtrace(uint64_t indent) const {
 
   while (true) {
     Value par = TRY(cur.parent());
-    // If parent frame is empty - we are at the top-level. Top-level is always
-    // <unnamed>, so let's just skip it
-    if (par.is<Nil>()) break;
-
     auto fun = TRY(cur.fun());
 
     for (uint64_t i = 0; i < indent; i++) {
       res = TRY(res.concat(" "));
     }
 
-    res = TRY(res.concat("Function "));
-    if (fun.is<Function>()) {
-      Function& f = *fun.to<Function>();
-      auto name = TRY(f.name());
-      if (!name.is<Symbol>()) {
-        name = Value(TRY(String::create("<unnamed>")));
-      } else {
-        name = Value(TRY(String::create(*name.to<Symbol>())));
+    if (cur.guard()) {
+      res = TRY(res.concat("guard"));
+    } else {
+      res = TRY(res.concat("Function "));
+      if (fun.is<Function>()) {
+        Function& f = *fun.to<Function>();
+        auto name = TRY(f.name());
+        if (!name.is<Symbol>()) {
+          name = Value(TRY(String::create("<unnamed>")));
+        } else {
+          name = Value(TRY(String::create(*name.to<Symbol>())));
+        }
+        res = TRY(res.concat(*name.to<String>()));
+      } else if (fun.is<StdlibFunction>()) {
+        StdlibFunction& f = *fun.to<StdlibFunction>();
+        auto name = TRY(String::create(TRY(f.name())));
+        res = TRY(res.concat(name));
       }
-      res = TRY(res.concat(*name.to<String>()));
-    } else if (fun.is<StdlibFunction>()) {
-      StdlibFunction& f = *fun.to<StdlibFunction>();
-      auto name = TRY(String::create(TRY(f.name())));
-      res = TRY(res.concat(name));
     }
 
     res = TRY(res.concat("\n"));
 
+    if (par.is<Nil>()) break;
+
     cur = TRY(par.to<StackFrame>()->copy());
   }
   return res;
@@ -541,7 +736,6 @@ Result<short> Error::cmp(const Error& rhs) const {
 Result<Continuation> Continuation::create(const Value& value,
                                           const StackFrame& frame) {
   auto pod = TRY(arena_alloc<PodContinuation>());
-  pod->header.tag = Tag::Continuation;
 
   pod->value = value.pod();
   pod->frame = frame.pod();
@@ -577,7 +771,6 @@ Result<short> Continuation::cmp(const Continuation& rhs) const {
 
 Result<Task> Task::create(uint64_t task_id, const Array& params) {
   auto pod = TRY(arena_alloc<PodTask>());
-  pod->header.tag = Tag::Task;
 
   pod->task_id = task_id;
   pod->params = params.pod();
@@ -614,7 +807,6 @@ Result<short> Task::cmp(const Task& rhs) const {
 
 Result<TaskResult> TaskResult::create(const Value& result, const Value& error) {
   auto pod = TRY(arena_alloc<PodTaskResult>());
-  pod->header.tag = Tag::TaskResult;
 
   pod->result = result.pod();
   pod->error = error.pod();
@@ -650,7 +842,6 @@ Result<short> TaskResult::cmp(const TaskResult& rhs) const {
 
 Result<Pair> Pair::create(const Value& first, const Value& rest) {
   auto pod = TRY(arena_alloc<PodPair>());
-  pod->header.tag = Tag::Pair;
   pod->first = first.pod();
   pod->rest = rest.pod();
 
@@ -719,7 +910,6 @@ Result<Function> Function::create(const Value& name, uint64_t arity,
                                   const Array& constants, const Array& code,
                                   const Array& closure) {
   auto pod = TRY(arena_alloc<PodFunction>());
-  pod->header.tag = Tag::Function;
   pod->arity = arity;
   pod->name = name.pod();
   pod->constants = constants.pod();
@@ -732,7 +922,6 @@ Result<Function> Function::create(const Value& name, uint64_t arity,
 Result<Function> Function::create(const Function& prototype,
                                   const Array& closure) {
   auto pod = TRY(arena_alloc<PodFunction>());
-  pod->header.tag = Tag::Function;
   pod->arity = prototype._value->arity;
   pod->name = prototype._value->name;
   pod->constants = prototype._value->constants;
@@ -760,7 +949,6 @@ Result<Array> Function::closure() const {
 
 Result<StdlibFunction> StdlibFunction::create(StdlibFunctionId fun_id) {
   auto pod = TRY(arena_alloc<PodStdlibFunction>());
-  pod->header.tag = Tag::StdlibFunction;
   pod->fun_id = (uint64_t)fun_id;
 
   return StdlibFunction(TRY(MkGcRoot(pod)));
@@ -778,7 +966,6 @@ StdlibFunctionId StdlibFunction::fun_id() const {
 
 Result<Module> Module::create(const Value& name, const Function& fun) {
   auto pod = TRY(arena_alloc<PodModule>());
-  pod->header.tag = Tag::Module;
   pod->name = name.pod();
   pod->fun = fun.pod();
 
@@ -847,7 +1034,6 @@ Result<Array> Array::set(uint64_t idx, const Value& value) const {
   if (idx >= res_size) return ERROR(IndexOutOfRange);
 
   auto pod = TRY(arena_alloc<PodArray>(res_size * sizeof(OffPtr<PodObject>)));
-  pod->header.tag = Tag::Array;
   pod->size = res_size;
   for (uint64_t i = 0; i < res_size; i++) {
     pod->data[i] = _value->data[i].get();
@@ -872,7 +1058,6 @@ Result<Array> Array::append(const Value& rhs) const {
   auto size = TRY(this->size());
 
   auto pod = TRY(arena_alloc<PodArray>(res_size * sizeof(OffPtr<PodObject>)));
-  pod->header.tag = Tag::Array;
   pod->size = res_size;
   for (uint64_t i = 0; i < size; i++) {
     pod->data[i] = _value->data[i].get();
@@ -930,7 +1115,6 @@ Result<Dict> Dict::set(const Value& key, const Value& value) const {
   }
 
   auto pod = TRY(arena_alloc<PodDict>(2 * s * sizeof(OffPtr<PodObject>)));
-  pod->header.tag = Tag::Dict;
   pod->size = s;
 
   auto vpod = _value.get();
@@ -1092,7 +1276,7 @@ Result<short> Dict::cmp(const Dict& rhs) const {
   uint64_t i = 0;
   uint64_t j = 0;
   while (1) {
-    if (i == lsize && j == lsize) return 0;
+    if (i == lsize && j == rsize) return 0;
 
     short cmp = short(i == lsize) - short(j == rsize);
     if (cmp != 0) return cmp;
@@ -1113,7 +1297,7 @@ Result<short> Array::cmp(const Array& rhs) const {
   uint64_t i = 0;
   uint64_t j = 0;
   while (1) {
-    if (i == lsize && j == lsize) return 0;
+    if (i == lsize && j == rsize) return 0;
 
     short cmp = short(i == lsize) - short(j == rsize);
     if (cmp != 0) return cmp;
diff --git a/src/common.hpp b/src/common.hpp
index 422e70a..9923fbe 100644
--- a/src/common.hpp
+++ b/src/common.hpp
@@ -166,7 +166,6 @@ class Nil : public Object {
 
   static Result<Nil> create() {
     auto pod = TRY(arena_alloc<PodNil>());
-    pod->header.tag = Tag::Nil;
 
     return Nil(TRY(MkGcRoot(pod)));
   }
@@ -209,7 +208,6 @@ class Array : public Object {
 
   static Result<Array> create() {
     auto pod = TRY(arena_alloc<PodArray>());
-    pod->header.tag = Tag::Array;
 
     pod->size = 0;
 
@@ -237,7 +235,6 @@ class Array : public Object {
     uint64_t res_size = lhs_size + rhs_size;
 
     auto pod = TRY(arena_alloc<PodArray>(res_size * sizeof(PodObject*)));
-    pod->header.tag = Tag::Array;
     pod->size = res_size;
     for (uint64_t i = 0; i < lhs_size; i++) {
       pod->data[i] = _value->data[i].get();
@@ -253,7 +250,6 @@ class Array : public Object {
     if (start > end) return ERROR(IndexOutOfRange);
     uint64_t res_size = end - start;
     auto pod = TRY(arena_alloc<PodArray>(res_size * sizeof(PodObject*)));
-    pod->header.tag = Tag::Array;
     pod->size = res_size;
     for (uint64_t i = 0; i < end - start; i++) {
       pod->data[i] = _value->data[start + i];
@@ -293,7 +289,6 @@ class ByteArray : public Object {
   }
   static Result<ByteArray> create(char* chars, int64_t size) {
     auto pod = TRY(arena_alloc<PodByteArray>(size * sizeof(char)));
-    pod->header.tag = Tag::ByteArray;
 
     memcpy(pod->data, chars, size * sizeof(char32_t));
     pod->size = size;
@@ -304,7 +299,6 @@ class ByteArray : public Object {
   static Result<ByteArray> create(const char* str) {
     uint64_t size = strlen(str);
     auto pod = TRY(arena_alloc<PodByteArray>(size * sizeof(char32_t)));
-    pod->header.tag = Tag::ByteArray;
 
     memcpy(pod->data, str, size);
     pod->size = size;
@@ -331,7 +325,6 @@ class ByteArray : public Object {
     uint64_t res_size = lhs_size + rhs_size;
 
     auto pod = TRY(arena_alloc<PodByteArray>(res_size * sizeof(char)));
-    pod->header.tag = Tag::ByteArray;
     pod->size = res_size;
     memcpy(pod->data, _value->data, sizeof(char) * lhs_size);
     memcpy(pod->data, rhs + lhs_size, sizeof(char) * rhs_size);
@@ -344,10 +337,9 @@ class ByteArray : public Object {
     uint64_t res_size = lhs_size + rhs_size;
 
     auto pod = TRY(arena_alloc<PodByteArray>(res_size * sizeof(char)));
-    pod->header.tag = Tag::ByteArray;
     pod->size = res_size;
     memcpy(pod->data, _value->data, sizeof(char) * lhs_size);
-    memcpy(pod->data, rhs + lhs_size, sizeof(char) * rhs_size);
+    memcpy(pod->data + lhs_size, rhs, sizeof(char) * rhs_size);
 
     return ByteArray(TRY(MkGcRoot(pod)));
   }
@@ -358,7 +350,6 @@ class ByteArray : public Object {
     uint64_t res_size = lhs_size + rhs_size;
 
     auto pod = TRY(arena_alloc<PodByteArray>(res_size * sizeof(char)));
-    pod->header.tag = Tag::ByteArray;
     pod->size = res_size;
     memcpy(pod->data, _value->data, sizeof(char) * lhs_size);
     memcpy(pod->data + lhs_size, rhs._value->data, sizeof(char) * rhs_size);
@@ -370,13 +361,16 @@ class ByteArray : public Object {
     if (start > end) return ERROR(IndexOutOfRange);
     uint64_t res_size = end - start;
     auto pod = TRY(arena_alloc<PodByteArray>(res_size * sizeof(char)));
-    pod->header.tag = Tag::ByteArray;
     pod->size = res_size;
     memcpy(pod->data, _value->data + start, sizeof(char) * res_size);
 
     return ByteArray(TRY(MkGcRoot(pod)));
   }
 
+  Result<String> hex() const;
+  Result<ByteArray> to_rle() const;
+  Result<ByteArray> from_rle() const;
+
  private:
   GcRoot<PodByteArray> _value;
 };
@@ -410,7 +404,6 @@ class Dict : public Object {
 
   static Result<Dict> create() {
     auto pod = TRY(arena_alloc<PodDict>());
-    pod->header.tag = Tag::Dict;
 
     pod->size = 0;
 
@@ -476,7 +469,7 @@ class String : public Object {
     uint64_t i = 0;
     uint64_t j = 0;
     while (1) {
-      if (i == lsize && j == lsize) return 0;
+      if (i == lsize && j == rsize) return 0;
 
       short cmp = short(i == lsize) - short(j == rsize);
       if (cmp != 0) return cmp;
@@ -498,7 +491,6 @@ class String : public Object {
   }
   static Result<String> create(char32_t* chars, int64_t size) {
     auto pod = TRY(arena_alloc<PodString>(size * sizeof(char32_t)));
-    pod->header.tag = Tag::String;
 
     memcpy(pod->data, chars, size * sizeof(char32_t));
     pod->size = size;
@@ -510,7 +502,6 @@ class String : public Object {
     auto size = TRY(bytes.size());
 
     auto pod = TRY(arena_alloc<PodString>(size * sizeof(char32_t)));
-    pod->header.tag = Tag::String;
 
     for (uint64_t i = 0; i < size; i++) pod->data[i] = TRY(bytes[i]);
     pod->size = size;
@@ -523,7 +514,6 @@ class String : public Object {
   static Result<String> create(const char* str) {
     uint64_t size = strlen(str);
     auto pod = TRY(arena_alloc<PodString>(size * sizeof(char32_t)));
-    pod->header.tag = Tag::String;
 
     for (uint64_t i = 0; i < size; i++) pod->data[i] = str[i];
     pod->size = size;
@@ -548,7 +538,6 @@ class String : public Object {
     uint64_t res_size = lhs_size + rhs_size;
 
     auto pod = TRY(arena_alloc<PodString>(res_size * sizeof(char32_t)));
-    pod->header.tag = Tag::String;
     pod->size = res_size;
     memcpy(pod->data, _value->data, sizeof(char32_t) * lhs_size);
     for (uint64_t i = 0; i < rhs_size; i++) pod->data[lhs_size + i] = rhs[i];
@@ -563,7 +552,6 @@ class String : public Object {
     uint64_t res_size = lhs_size + rhs_size;
 
     auto pod = TRY(arena_alloc<PodString>(res_size * sizeof(char32_t)));
-    pod->header.tag = Tag::String;
     pod->size = res_size;
     memcpy(pod->data, _value->data, sizeof(char32_t) * lhs_size);
     for (uint64_t i = 0; i < rhs_size; i++) pod->data[lhs_size + i] = rhs[i];
@@ -577,7 +565,6 @@ class String : public Object {
     uint64_t res_size = lhs_size + rhs_size;
 
     auto pod = TRY(arena_alloc<PodString>(res_size * sizeof(char32_t)));
-    pod->header.tag = Tag::String;
     pod->size = res_size;
     memcpy(pod->data, _value->data, sizeof(char32_t) * lhs_size);
     memcpy(pod->data + lhs_size, rhs._value->data, sizeof(char32_t) * rhs_size);
@@ -589,7 +576,6 @@ class String : public Object {
     if (start > end) return ERROR(IndexOutOfRange);
     uint64_t res_size = end - start;
     auto pod = TRY(arena_alloc<PodString>(res_size * sizeof(char32_t)));
-    pod->header.tag = Tag::String;
     pod->size = res_size;
     memcpy(pod->data, _value->data + start, sizeof(char32_t) * res_size);
 
@@ -620,7 +606,7 @@ class Symbol : public Object {
     uint64_t i = 0;
     uint64_t j = 0;
     while (1) {
-      if (i == lsize && j == lsize) return 0;
+      if (i == lsize && j == rsize) return 0;
 
       short cmp = short(i == lsize) - short(j == rsize);
       if (cmp != 0) return cmp;
@@ -662,7 +648,6 @@ class Symbol : public Object {
 
   static Result<Symbol> create(char32_t* chars, int64_t size) {
     auto pod = TRY(arena_alloc<PodSymbol>(size * sizeof(char32_t)));
-    pod->header.tag = Tag::Symbol;
 
     memcpy(pod->data, chars, size * sizeof(char32_t));
 
@@ -672,7 +657,6 @@ class Symbol : public Object {
   static Result<Symbol> create(const char* str) {
     uint64_t size = strlen(str);
     auto pod = TRY(arena_alloc<PodSymbol>(size * sizeof(char32_t)));
-    pod->header.tag = Tag::Symbol;
 
     for (uint64_t i = 0; i < size; i++) pod->data[i] = str[i];
     pod->size = size;
@@ -717,7 +701,6 @@ class SrcLoc : public Object {
   static Result<SrcLoc> create(const SourcePosition& start,
                                const SourcePosition& end) {
     auto pod = TRY(arena_alloc<PodSrcLoc>());
-    pod->header.tag = Tag::SrcLoc;
 
     pod->sourcerange.start = start;
     pod->sourcerange.end = end;
@@ -849,9 +832,8 @@ class Int64 : public Object {
     return Int64(TRY(MkGcRoot(obj)));
   }
 
-  static Result<Int64> create(double val) {
+  static Result<Int64> create(int64_t val) {
     auto pod = TRY(arena_alloc<PodInt64>());
-    pod->header.tag = Tag::Int64;
     pod->value = val;
 
     return Int64(TRY(MkGcRoot(pod)));
@@ -908,7 +890,6 @@ class Float : public Object {
 
   static Result<Float> create(double val) {
     auto pod = TRY(arena_alloc<PodFloat>());
-    pod->header.tag = Tag::Float;
     pod->value = val;
 
     return Float(TRY(MkGcRoot(pod)));
@@ -945,7 +926,6 @@ class Bool : public Object {
 
   static Result<Bool> create(bool val) {
     auto pod = TRY(arena_alloc<PodBool>());
-    pod->header.tag = Tag::Bool;
     pod->value = val;
 
     return Bool(TRY(MkGcRoot(pod)));
@@ -983,7 +963,6 @@ class Opcode : public Object {
                                OpArg arg2 = {0, 0}, OpArg arg3 = {0, 0},
                                OpArg arg4 = {0, 0}) {
     auto pod = TRY(arena_alloc<PodOpcode>());
-    pod->header.tag = Tag::Opcode;
     pod->opcode = opcode;
     pod->arg1 = arg1;
     pod->arg2 = arg2;
@@ -1164,13 +1143,13 @@ class StackFrame : public Object {
   Result<StackFrame> incpc();
   Result<uint64_t> size() const { return _value->size; }
 
-  static Result<StackFrame> create(const Value& parent, const Value& fun);
+  static Result<StackFrame> create(const Value& parent, const Value& fun,
+                                   bool guard = false);
 
   Result<Array> slice(uint64_t start, uint64_t end) const {
     if (start > end || end > _value->size) return ERROR(IndexOutOfRange);
     uint64_t res_size = end - start;
     auto pod = TRY(arena_alloc<PodArray>(res_size * sizeof(PodObject*)));
-    pod->header.tag = Tag::Array;
     pod->size = res_size;
     for (uint64_t i = 0; i < end - start; i++) {
       pod->data[i] = _value->data[start + i];
@@ -1182,9 +1161,16 @@ class StackFrame : public Object {
   Result<StackFrame> call(const Value& fun, uint64_t start, uint64_t end) const;
   Result<StackFrame> ret(uint64_t regno) const;
 
+  Result<StackFrame> detach(uint64_t depth) const;
+  Result<StackFrame> attach(const StackFrame& frame) const;
+
+  Result<StackFrame> set_guard(bool guard = true) const;
+
   virtual Result<Value> copy_value() const final;
   Result<StackFrame> copy() const;
 
+  bool guard() const { return _value->guard; }
+
   Result<String> backtrace(uint64_t indent = 0) const;
 
  private:
@@ -1215,7 +1201,6 @@ class Error : public Object {
     auto message_str = TRY(String::create(message));
 
     auto pod = TRY(arena_alloc<PodError>());
-    pod->header.tag = Tag::Error;
 
     pod->name = name_str.pod();
     pod->message = message_str.pod();
@@ -1225,7 +1210,6 @@ class Error : public Object {
 
   static Result<Error> create(const Symbol& name, const String& message) {
     auto pod = TRY(arena_alloc<PodError>());
-    pod->header.tag = Tag::Error;
 
     pod->name = name.pod();
     pod->message = message.pod();
diff --git a/src/error.cpp b/src/error.cpp
index e3c8701..e2ae8c5 100644
--- a/src/error.cpp
+++ b/src/error.cpp
@@ -19,9 +19,58 @@ void reseterrobj() { errobj = Value(); }
 
 const char* errname(ErrorCode errcode) {
   switch (errcode) {
+    case ErrorCode::Success:
+      return "success";
+    case ErrorCode::Unknown:
+      return "unknown";
+    case ErrorCode::OutOfMemory:
+      return "out-of-memory";
+    case ErrorCode::IndexOutOfRange:
+      return "index-out-of-range";
+    case ErrorCode::TypeMismatch:
+      return "type-mismatch";
+    case ErrorCode::ReadError:
+      return "read-error";
+    case ErrorCode::UnterminatedStringLiteral:
+      return "unterminalted-string-literal";
+    case ErrorCode::InvalidNumericLiteral:
+      return "invalid-numeric-literal";
+    case ErrorCode::NotImplemented:
+      return "not-implemented";
+    case ErrorCode::InvalidSymbol:
+      return "invalid-symbol";
+    case ErrorCode::MalformedList:
+      return "malformed-list";
+    case ErrorCode::KeyError:
+      return "key-error";
+    case ErrorCode::EndOfProgram:
+      return "end-of-program";
+    case ErrorCode::CompilationError:
+      return "compilation-error";
+    case ErrorCode::ArgumentCountMismatch:
+      return "argument-count-mismatch";
+    case ErrorCode::IOError:
+      return "io-error";
+    case ErrorCode::Interrupt:
+      return "interrupt";
+    case ErrorCode::AssertionFailed:
+      return "assertion-failed";
+    case ErrorCode::DivisionByZero:
+      return "division-by-zero";
     case ErrorCode::SyntaxError:
       return "syntax-error";
-    default:
-      return "unknown";
+    case ErrorCode::RuntimeError:
+      return "runtime-error";
+    case ErrorCode::Raise:
+      return "raise";
+    case ErrorCode::TaskFailed:
+      return "task-failed";
   }
+  return "";
+}
+
+Result<Value> wrap_error(ErrorCode code) {
+  auto name = errname(code);
+  auto message = geterr();
+  return Value(TRY(Error::create(name, message)));
 }
diff --git a/src/error.hpp b/src/error.hpp
index 1d6d8c0..65d8b85 100644
--- a/src/error.hpp
+++ b/src/error.hpp
@@ -40,6 +40,8 @@ const Value& geterrobj(void);
 Result<void> seterrobj(const Value&);
 void reseterrobj();
 
+Result<Value> wrap_error(ErrorCode code);
+
 #define STRINGIZE_NESTED(A) #A
 #define STRINGIZE(A) STRINGIZE_NESTED(A)
 
diff --git a/src/fio.cpp b/src/fio.cpp
index 922f338..9204f07 100644
--- a/src/fio.cpp
+++ b/src/fio.cpp
@@ -63,7 +63,7 @@ Result<ByteArray> read_file(const char* filename) {
 }
 
 Result<ByteArray> read_file(const ByteArray& filename) {
-  auto filename_bytes = TRY(filename.concat("\0"));
+  auto filename_bytes = TRY(filename.concat("\0", 1));
   FILE* fh = fopen(filename_bytes.raw_bytes(), "r");
 
   if (!fh) {
@@ -78,7 +78,7 @@ Result<ByteArray> read_file(const ByteArray& filename) {
 Result<ByteArray> read_stdin() { return read_fh(stdin); }
 
 Result<void> write_file(const ByteArray& filename, const ByteArray& contents) {
-  auto filename_bytes = TRY(filename.concat("\0"));
+  auto filename_bytes = TRY(filename.concat("\0", 1));
   FILE* fh = fopen(filename_bytes.raw_bytes(), "w");
 
   if (!fh) {
diff --git a/src/pod.hpp b/src/pod.hpp
index 2953121..001229c 100644
--- a/src/pod.hpp
+++ b/src/pod.hpp
@@ -201,6 +201,7 @@ class PodStackFrame final : public PodObject {
 
   OffPtr<PodObject> parent;
   OffPtr<PodObject> fun;
+  bool guard;
   uint64_t pc;
   uint64_t size;
   OffPtr<PodObject> data[];
diff --git a/src/serialize.cpp b/src/serialize.cpp
new file mode 100644
index 0000000..49da110
--- /dev/null
+++ b/src/serialize.cpp
@@ -0,0 +1,395 @@
+#include "serialize.hpp"
+
+#include "arena.hpp"
+#include "common.hpp"
+#include "pod.hpp"
+
+class Serializer {
+ public:
+  Serializer(uint8_t* buf, bool dryrun)
+      : buf(buf), _offset(0), dryrun(dryrun) {}
+
+  PodObject* serialize_nil(PodNil* obj) {
+    PodNil* res = (PodNil*)(buf + _offset);
+    if (!dryrun) {
+      memcpy(res, obj, sizeof(PodNil));
+    }
+
+    _offset += round_up(sizeof(PodNil), 8);
+    return res;
+  }
+  PodObject* serialize_bool(PodBool* obj) {
+    PodBool* res = (PodBool*)(buf + _offset);
+    if (!dryrun) {
+      memcpy(res, obj, sizeof(PodBool));
+    }
+
+    _offset += round_up(sizeof(PodBool), 8);
+    return res;
+  }
+  PodObject* serialize_int64(PodInt64* obj) {
+    PodInt64* res = (PodInt64*)(buf + _offset);
+    if (!dryrun) {
+      memcpy(res, obj, sizeof(PodInt64));
+    }
+
+    _offset += sizeof(PodInt64);
+    return res;
+  }
+  PodObject* serialize_float(PodFloat* obj) {
+    PodFloat* res = (PodFloat*)(buf + _offset);
+    if (!dryrun) {
+      memcpy(res, obj, sizeof(PodFloat));
+    }
+
+    _offset += round_up(sizeof(PodFloat), 8);
+    return res;
+  }
+  PodObject* serialize_string(PodString* obj) {
+    PodString* res = (PodString*)(buf + _offset);
+    uint64_t size = sizeof(PodString) + sizeof(char32_t) * obj->size;
+    if (!dryrun) {
+      memcpy(res, obj, size);
+    }
+
+    _offset += round_up(size, 8);
+    return res;
+  }
+  PodObject* serialize_symbol(PodSymbol* obj) {
+    PodSymbol* res = (PodSymbol*)(buf + _offset);
+    uint64_t size = sizeof(PodSymbol) + sizeof(char32_t) * obj->size;
+    if (!dryrun) {
+      memcpy(res, obj, size);
+    }
+
+    _offset += round_up(size, 8);
+    return res;
+  }
+  PodObject* serialize_srcloc(PodSrcLoc* obj) {
+    PodSrcLoc* res = (PodSrcLoc*)(buf + _offset);
+    uint64_t size = sizeof(PodSrcLoc);
+    if (!dryrun) {
+      memcpy(res, obj, size);
+    }
+
+    _offset += round_up(size, 8);
+    return res;
+  }
+  PodObject* serialize_syntax(PodSyntax* obj) {
+    PodSyntax* res = (PodSyntax*)(buf + _offset);
+    uint64_t size = sizeof(PodSyntax);
+    _offset += round_up(size, 8);
+
+    auto filename = serialize_object(obj->filename.get());
+    auto srcloc = serialize_object(obj->srcloc.get());
+    auto expression = serialize_object(obj->expression.get());
+    if (!dryrun) {
+      res->header.tag = Tag::Syntax;
+      res->filename = filename;
+      res->srcloc = srcloc;
+      res->expression = expression;
+    }
+
+    return res;
+  }
+  PodObject* serialize_pair(PodPair* obj) {
+    PodPair* res = (PodPair*)(buf + _offset);
+    uint64_t size = sizeof(PodPair);
+    _offset += round_up(size, 8);
+
+    auto first = serialize_object(obj->first.get());
+    auto rest = serialize_object(obj->rest.get());
+    if (!dryrun) {
+      res->header.tag = Tag::Pair;
+      res->first = first;
+      res->rest = rest;
+    }
+
+    return res;
+  }
+  PodObject* serialize_array(PodArray* obj) {
+    PodArray* res = (PodArray*)(buf + _offset);
+    uint64_t size = sizeof(PodArray) + sizeof(OffPtr<PodObject>) * obj->size;
+    _offset += round_up(size, 8);
+
+    if (!dryrun) {
+      res->header.tag = Tag::Array;
+      res->size = obj->size;
+    }
+
+    for (uint64_t i = 0; i < obj->size; ++i) {
+      auto val = serialize_object(obj->data[i].get());
+      if (!dryrun) {
+        res->data[i] = val;
+      }
+    }
+
+    return res;
+  }
+  PodObject* serialize_bytearray(PodByteArray* obj) {
+    PodByteArray* res = (PodByteArray*)(buf + _offset);
+    uint64_t size = sizeof(PodArray) + obj->size;
+    _offset += round_up(size, 8);
+
+    if (!dryrun) {
+      res->header.tag = Tag::ByteArray;
+      memcpy(res, obj, size);
+    }
+
+    return res;
+  }
+  PodObject* serialize_dict(PodDict* obj) {
+    PodDict* res = (PodDict*)(buf + _offset);
+    uint64_t size = sizeof(PodDict) + sizeof(OffPtr<PodObject>) * obj->size * 2;
+    _offset += round_up(size, 8);
+
+    if (!dryrun) {
+      res->header.tag = Tag::Dict;
+      res->size = obj->size;
+    }
+
+    for (uint64_t i = 0; i < obj->size * 2; ++i) {
+      auto val = serialize_object(obj->data[i].get());
+      if (!dryrun) {
+        res->data[i] = val;
+      }
+    }
+
+    return res;
+  }
+
+  PodObject* serialize_opcode(PodOpcode* obj) {
+    PodOpcode* res = (PodOpcode*)(buf + _offset);
+    uint64_t size = sizeof(PodOpcode);
+    _offset += round_up(size, 8);
+
+    if (!dryrun) {
+      memcpy(res, obj, size);
+    }
+
+    return res;
+  }
+  PodObject* serialize_function(PodFunction* obj) {
+    PodFunction* res = (PodFunction*)(buf + _offset);
+    uint64_t size = sizeof(PodFunction);
+    _offset += round_up(size, 8);
+
+    auto closure = serialize_object(obj->closure.get());
+    auto code = serialize_object(obj->code.get());
+    auto constants = serialize_object(obj->constants.get());
+    auto name = serialize_object(obj->name.get());
+
+    if (!dryrun) {
+      res->header.tag = Tag::Function;
+      res->arity = obj->arity;
+      res->closure = closure;
+      res->code = code;
+      res->constants = constants;
+      res->name = name;
+    }
+
+    return res;
+  }
+  PodObject* serialize_stdlib_function(PodStdlibFunction* obj) {
+    PodStdlibFunction* res = (PodStdlibFunction*)(buf + _offset);
+    uint64_t size = sizeof(PodStdlibFunction);
+    _offset += round_up(size, 8);
+
+    if (!dryrun) {
+      memcpy(res, obj, size);
+    }
+
+    return res;
+  }
+  PodObject* serialize_module(PodModule* obj) {
+    PodModule* res = (PodModule*)(buf + _offset);
+    uint64_t size = sizeof(PodModule);
+    _offset += round_up(size, 8);
+
+    auto fun = serialize_object(obj->fun.get());
+    auto name = serialize_object(obj->name.get());
+
+    if (!dryrun) {
+      res->header.tag = Tag::Module;
+      res->fun = fun;
+      res->name = name;
+    }
+
+    return res;
+  }
+  PodObject* serialize_stack(PodStackFrame* obj) {
+    PodStackFrame* res = (PodStackFrame*)(buf + _offset);
+    uint64_t size =
+        sizeof(PodStackFrame) + sizeof(OffPtr<PodObject>) * obj->size;
+    _offset += round_up(size, 8);
+
+    auto fun = serialize_object(obj->fun.get());
+    auto parent = serialize_object(obj->parent.get());
+
+    if (!dryrun) {
+      res->header.tag = Tag::StackFrame;
+      res->fun = fun;
+      res->parent = parent;
+      res->pc = obj->pc;
+      res->size = obj->size;
+      res->guard = obj->guard;
+    }
+
+    for (uint64_t i = 0; i < obj->size; i++) {
+      auto val = serialize_object(obj->data[i].get());
+      if (!dryrun) {
+        res->data[i] = val;
+      }
+    }
+
+    return res;
+  }
+  PodObject* serialize_error(PodError* obj) {
+    PodError* res = (PodError*)(buf + _offset);
+    uint64_t size = sizeof(PodError);
+    _offset += round_up(size, 8);
+
+    auto name = serialize_object(obj->name.get());
+    auto message = serialize_object(obj->message.get());
+
+    if (!dryrun) {
+      res->header.tag = Tag::Error;
+      res->name = name;
+      res->message = message;
+    }
+
+    return res;
+  }
+
+  PodObject* serialize_continuation(PodContinuation* obj) {
+    PodContinuation* res = (PodContinuation*)(buf + _offset);
+    uint64_t size = sizeof(PodContinuation);
+    _offset += round_up(size, 8);
+
+    auto frame = serialize_object(obj->frame.get());
+    auto value = serialize_object(obj->value.get());
+
+    if (!dryrun) {
+      res->header.tag = Tag::Continuation;
+      res->frame = frame;
+      res->value = value;
+    }
+
+    return res;
+  }
+  PodObject* serialize_task(PodTask* obj) {
+    PodTask* res = (PodTask*)(buf + _offset);
+    uint64_t size = sizeof(PodTask);
+    _offset += round_up(size, 8);
+
+    auto params = serialize_object(obj->params.get());
+
+    if (!dryrun) {
+      res->header.tag = Tag::Task;
+      res->task_id = obj->task_id;
+      res->params = params;
+    }
+
+    return res;
+  }
+  PodObject* serialize_task_result(PodTaskResult* obj) {
+    PodTaskResult* res = (PodTaskResult*)(buf + _offset);
+    uint64_t size = sizeof(PodTaskResult);
+    _offset += round_up(size, 8);
+
+    auto result = serialize_object(obj->result.get());
+    auto error = serialize_object(obj->error.get());
+
+    if (!dryrun) {
+      res->header.tag = Tag::TaskResult;
+      res->result = result;
+      res->error = error;
+    }
+
+    return res;
+  }
+
+  PodObject* serialize_object(PodObject* obj) {
+    switch (obj->header.tag) {
+      case Tag::Nil:
+        return serialize_nil((PodNil*)obj);
+      case Tag::Bool:
+        return serialize_bool((PodBool*)obj);
+      case Tag::Int64:
+        return serialize_int64((PodInt64*)obj);
+      case Tag::Float:
+        return serialize_float((PodFloat*)obj);
+      case Tag::String:
+        return serialize_string((PodString*)obj);
+      case Tag::Symbol:
+        return serialize_symbol((PodSymbol*)obj);
+      case Tag::SrcLoc:
+        return serialize_srcloc((PodSrcLoc*)obj);
+      case Tag::Syntax:
+        return serialize_syntax((PodSyntax*)obj);
+      case Tag::Pair:
+        return serialize_pair((PodPair*)obj);
+      case Tag::Array:
+        return serialize_array((PodArray*)obj);
+      case Tag::ByteArray:
+        return serialize_bytearray((PodByteArray*)obj);
+      case Tag::Dict:
+        return serialize_dict((PodDict*)obj);
+      case Tag::Opcode:
+        return serialize_opcode((PodOpcode*)obj);
+      case Tag::Function:
+        return serialize_function((PodFunction*)obj);
+      case Tag::StdlibFunction:
+        return serialize_stdlib_function((PodStdlibFunction*)obj);
+      case Tag::Module:
+        return serialize_module((PodModule*)obj);
+      case Tag::StackFrame:
+        return serialize_stack((PodStackFrame*)obj);
+      case Tag::Error:
+        return serialize_error((PodError*)obj);
+      case Tag::Continuation:
+        return serialize_continuation((PodContinuation*)obj);
+      case Tag::Task:
+        return serialize_task((PodTask*)obj);
+      case Tag::TaskResult:
+        return serialize_task_result((PodTaskResult*)obj);
+    };
+
+    // Should never reach here
+    return 0;
+  }
+
+  uint64_t offset() { return _offset; }
+
+ private:
+  uint8_t* buf;
+  uint64_t _offset;
+  bool dryrun;
+};
+
+Result<ByteArray> serialize(const Value& val) {
+  Serializer s(0, true);
+  s.serialize_object(val.pod());
+  auto size = s.offset();
+
+  auto pod = TRY(arena_alloc<PodByteArray>(size * sizeof(char)));
+
+  pod->size = size;
+  Serializer ss((uint8_t*)pod->data, false);
+  ss.serialize_object(val.pod());
+
+  auto ba = ByteArray(TRY(MkGcRoot(pod)));
+  ba = TRY(ba.to_rle());
+
+  return ba;
+}
+
+Result<Value> deserialize(const ByteArray& val) {
+  auto decompressed = TRY(val.from_rle());
+
+  auto size = TRY(decompressed.size());
+  PodObject* obj = TRY(arena_alloc_bytes<PodObject>(size));
+  memcpy(obj, decompressed.raw_bytes(), size);
+
+  return TRY(Value::create(obj));
+}
diff --git a/src/serialize.hpp b/src/serialize.hpp
new file mode 100644
index 0000000..230eaac
--- /dev/null
+++ b/src/serialize.hpp
@@ -0,0 +1,9 @@
+#pragma once
+
+template <class T>
+class Result;
+class Value;
+class ByteArray;
+
+Result<ByteArray> serialize(const Value& val);
+Result<Value> deserialize(const ByteArray& val);
diff --git a/src/stdlib.cpp b/src/stdlib.cpp
index b5d1e10..b666074 100644
--- a/src/stdlib.cpp
+++ b/src/stdlib.cpp
@@ -4,6 +4,7 @@
 #include "error.hpp"
 #include "fio.hpp"
 #include "pod.hpp"
+#include "serialize.hpp"
 #include "sourcerange.hpp"
 #include "writer.hpp"
 
@@ -391,7 +392,7 @@ Result<StackFrame> stdlib_raise(const StackFrame& stack) {
   auto stack_size = TRY(stack.size());
 
   if (stack_size > 1) {
-    return task_return(stack, 1);
+    return TRY(stack.ret(1));
   }
 
   auto params = TRY(stack.get(0));
@@ -434,6 +435,103 @@ Result<StackFrame> stdlib_task(const StackFrame& stack) {
   return res;
 }
 
+Result<StackFrame> stdlib_guard(const StackFrame& stack) {
+  auto stack_size = TRY(stack.size());
+  auto params = TRY(stack.get(0));
+  Array& params_array = *params.to<Array>();
+
+  auto size = TRY(params.size());
+  if (size != 2) return ERROR(ArgumentCountMismatch);
+
+  if (stack_size == 1) {
+    // This is the first entry to "guard", so need to establish
+    // context and call the guarded function
+    Value fun = TRY(params_array.get(0));
+
+    auto new_frame = TRY(stack.set_guard(true));
+    // Set stack[1] to "0", meaning that we've entered the guarded
+    // function
+    new_frame = TRY(new_frame.set(1, Value(TRY(Int64::create((int64_t)0)))));
+    new_frame = TRY(new_frame.set(2, fun));
+
+    return new_frame.call(fun, 2, 3);
+  }
+
+  auto state = TRY(stack.get(1));
+  if (!state.is<Int64>()) return ERROR(TypeMismatch);
+  auto state_int = state.to<Int64>()->value();
+
+  if (state_int == 0) {
+    // We've just normally returned from the guarded function. Just return
+    // its results back to the caller.
+
+    return stack.ret(2);
+  }
+
+  if (state_int == 1) {
+    // Exception has occured, and continuation is on the stack. We should
+    // now call the exception handler.
+    Value handler = TRY(params_array.get(1));
+
+    // Set stack[1] to "2", meaning that we've entered the guarded
+    // function
+    auto new_frame = TRY(stack.set(1, Value(TRY(Int64::create((int64_t)2)))));
+    auto cont = TRY(new_frame.get(2));
+    if (!cont.is<Continuation>()) return ERROR(TypeMismatch);
+    auto val = TRY(cont.to<Continuation>()->value());
+    new_frame = TRY(new_frame.set(2, handler));
+    new_frame = TRY(new_frame.set(3, val));
+    new_frame = TRY(new_frame.set(4, cont));
+
+    return new_frame.call(handler, 2, 5);
+  }
+
+  if (state_int == 2) {
+    // We've returned from the exception handler. Propagate its result to
+    // the caller.
+
+    return stack.ret(2);
+  }
+
+  return ERROR(NotImplemented);
+}
+
+Result<StackFrame> stdlib_serialize(const StackFrame& stack) {
+  auto stack_size = TRY(stack.size());
+  auto params = TRY(stack.get(0));
+  Array& params_array = *params.to<Array>();
+
+  auto size = TRY(params.size());
+  if (size != 1) return ERROR(ArgumentCountMismatch);
+
+  auto val = TRY(params.get(0));
+  auto serialized = Value(TRY(serialize(val)));
+
+  auto res = TRY(stack.set(0, serialized));
+
+  res = TRY(res.ret(0));
+
+  return res;
+}
+
+Result<StackFrame> stdlib_deserialize(const StackFrame& stack) {
+  auto stack_size = TRY(stack.size());
+  auto params = TRY(stack.get(0));
+  Array& params_array = *params.to<Array>();
+
+  auto size = TRY(params.size());
+  if (size != 1) return ERROR(ArgumentCountMismatch);
+
+  auto val = TRY(params.get(0));
+  if (!val.is<ByteArray>()) return ERROR(TypeMismatch);
+  auto deserialized = TRY(deserialize(*val.to<ByteArray>()));
+
+  auto res = TRY(stack.set(0, deserialized));
+
+  res = TRY(res.ret(0));
+
+  return res;
+}
 #define STDLIB_FUNCTION(name, id)                                  \
   [(uint64_t)StdlibFunctionId::id] = {#name, StdlibFunctionId::id, \
                                       stdlib_##name}
@@ -457,6 +555,9 @@ static StdlibFunctionEntry function_entries[] = {
     STDLIB_FUNCTION(error, Error),
     STDLIB_FUNCTION(raise, Raise),
     STDLIB_FUNCTION(task, Task),
+    STDLIB_FUNCTION(guard, Guard),
+    STDLIB_FUNCTION(serialize, Serialize),
+    STDLIB_FUNCTION(deserialize, Deserialize),
     [(uint64_t)StdlibFunctionId::Max] = {0, StdlibFunctionId::Max,
                                          stdlib_unknown},
 };
diff --git a/src/stdlib.hpp b/src/stdlib.hpp
index 9b91129..d27c56c 100644
--- a/src/stdlib.hpp
+++ b/src/stdlib.hpp
@@ -23,6 +23,9 @@ enum class StdlibFunctionId : uint64_t {
   Error,
   Raise,
   Task,
+  Guard,
+  Serialize,
+  Deserialize,
   Max,
 };
 
diff --git a/src/valeri.cpp b/src/valeri.cpp
index 3391551..4b697f9 100644
--- a/src/valeri.cpp
+++ b/src/valeri.cpp
@@ -22,6 +22,16 @@ Result<void> print_error(const Result<Value>& res, const String& backtrace) {
       auto message = TRY(errobj.to<Error>()->message());
       print_string(*message.to<String>());
       std::cout << "\n";
+    } else if (errobj.is<Continuation>()) {
+      auto val = TRY(errobj.to<Continuation>()->value());
+      if (val.is<Error>()) {
+        auto message = TRY(val.to<Error>()->message());
+        print_string(*message.to<String>());
+        std::cout << "\n";
+      } else {
+        std::cout << "Continuation: ";
+        debug_print(val);
+      }
     } else {
       std::cout << "Uncaught error: ";
       debug_print(errobj);
@@ -61,6 +71,7 @@ Result<Value> run_string(const String& fname, const String& src) {
   if (maybe_res.has_error()) {
     auto backtrace = TRY(vm.backtrace(2));
     print_error(maybe_res, backtrace);
+    return maybe_res;
   }
 
   return maybe_res.release_value();
diff --git a/src/vm.cpp b/src/vm.cpp
index 0b321db..0fb83da 100644
--- a/src/vm.cpp
+++ b/src/vm.cpp
@@ -124,6 +124,23 @@ Result<void> VM::vm_call_stdlib(Opcode& oc, StdlibFunction& fun) {
   return Result<void>();
 }
 
+Result<void> VM::vm_call_cont(Opcode& oc, Continuation& fun) {
+  uint64_t reg_start = (uint64_t)oc.arg1().arg;
+  uint64_t reg_end = (uint64_t)oc.arg2().arg;
+
+  if (reg_end - reg_start != 2) return ERROR(ArgumentCountMismatch);
+
+  auto param = TRY(_stack.get(reg_start + 1));
+  _stack = TRY(_stack.settop(reg_start));
+
+  auto cont_stack = TRY(fun.frame());
+  _stack = TRY(_stack.incpc());
+  _stack = TRY(cont_stack.attach(_stack));
+  _stack = TRY(_stack.set(TRY(_stack.size()), param));
+
+  return Result<void>();
+}
+
 Result<void> VM::vm_call(Opcode& oc) {
   Value fun_value = TRY(get(oc.arg1().is_const, oc.arg1().arg));
   if (fun_value.is<Function>()) {
@@ -136,6 +153,11 @@ Result<void> VM::vm_call(Opcode& oc) {
     return vm_call_stdlib(oc, fun);
   }
 
+  if (fun_value.is<Continuation>()) {
+    Continuation& fun = *fun_value.to<Continuation>();
+    return vm_call_cont(oc, fun);
+  }
+
   return ERROR(TypeMismatch);
 }
 
@@ -280,18 +302,58 @@ Result<void> VM::step_bytecode() {
   return Result<void>();
 }
 
+Result<Value> VM::unwind(const Continuation& cont) {
+  StackFrame cur = TRY(cont.frame());
+
+  uint64_t depth = 0;
+  while (true) {
+    if (cur.guard()) {
+      auto state = TRY(cur.get(1));
+      if (!state.is<Int64>()) return ERROR(TypeMismatch);
+      auto state_int = state.to<Int64>()->value();
+
+      if (state_int <= 1) {
+        auto val = TRY(cont.value());
+        auto cont_stack = TRY(cont.frame());
+        cont_stack = TRY(cont_stack.detach(depth - 1));
+
+        auto new_cont = TRY(Continuation::create(val, cont_stack));
+
+        cur = TRY(cur.set(1, Value(TRY(Int64::create((int64_t)1)))));
+        cur = TRY(cur.set(2, Value(std::move(new_cont))));
+        return Value(std::move(cur));
+      }
+    }
+
+    auto parent = TRY(cur.parent());
+    if (parent.is<Nil>()) break;
+
+    cur = TRY(parent.to<StackFrame>()->copy());
+    ++depth;
+  }
+  return Value(TRY(Nil::create()));
+}
+
 Result<StackFrame> VM::handle_raise(const Continuation& cont) {
   // TODO: this should do proper stack unwinding
+
+  auto unwind_res = TRY(unwind(cont));
+
+  if (!unwind_res.is<Nil>()) {
+    auto new_stack = TRY(unwind_res.to<StackFrame>()->copy());
+    return new_stack;
+  }
+
   auto value = TRY(cont.value());
 
-  if (value.is<Error>()) {
+  if (!value.is<Task>()) {
     auto obj = TRY(cont.copy_value());
     return ERROR_OBJ(Raise, obj);
   }
 
-  Value tr;
-
   if (value.is<Task>()) {
+    Value tr;
+
     auto task_id = value.to<Task>()->task_id();
     auto params = TRY(value.to<Task>()->params());
 
@@ -301,7 +363,7 @@ Result<StackFrame> VM::handle_raise(const Continuation& cont) {
       const auto& err = geterrobj();
       Value errobj;
       if (err.is<Nil>()) {
-        errobj = Value(TRY(Error::create("unknown-error", "Unknown error")));
+        errobj = TRY(wrap_error(res.error()));
       } else {
         errobj = TRY(err.copy());
       }
@@ -317,6 +379,7 @@ Result<StackFrame> VM::handle_raise(const Continuation& cont) {
     auto new_frame = frame.set(TRY(frame.size()), tr);
     return new_frame;
   }
+
   return ERROR(TypeMismatch);
 }
 
@@ -341,8 +404,12 @@ Result<void> VM::step() {
   }
 
   if (res.has_error()) {
+    if (res.error() == ErrorCode::EndOfProgram) return res;
+
     auto obj = TRY(geterrobj().copy());
-    if (obj.is<Nil>()) return res;
+    if (obj.is<Nil>()) {
+      obj = TRY(wrap_error(res.error()));
+    }
 
     if (res.error() == ErrorCode::Raise) {
       if (obj.is<Continuation>()) {
diff --git a/src/vm.hpp b/src/vm.hpp
index 1b20728..fec214a 100644
--- a/src/vm.hpp
+++ b/src/vm.hpp
@@ -49,6 +49,7 @@ class VM {
   Result<void> vm_selfcall(Opcode& oc);
   Result<void> vm_call_lisp(Opcode& oc, Function& fun);
   Result<void> vm_call_stdlib(Opcode& oc, StdlibFunction& fun);
+  Result<void> vm_call_cont(Opcode& oc, Continuation& fun);
   Result<void> vm_ret(Opcode& oc);
 
   Result<void> vm_equal(Opcode& oc);
@@ -62,6 +63,7 @@ class VM {
   Result<void> vm_global_load(Opcode& oc);
   Result<void> vm_global_store(Opcode& oc);
 
+  Result<Value> unwind(const Continuation& cont);
   Result<StackFrame> handle_raise(const Continuation& cont);
 
   Result<Value> get(bool is_const, uint64_t idx);
diff --git a/src/writer.cpp b/src/writer.cpp
index 492f7c0..b591194 100644
--- a/src/writer.cpp
+++ b/src/writer.cpp
@@ -122,7 +122,12 @@ Result<String> Writer::write_bool(const Bool& val) {
 }
 
 Result<String> Writer::write_bytearray(const ByteArray& val) {
-  return ERROR(NotImplemented);
+  String res = TRY(String::create("#<bytearray "));
+
+  res = TRY(res.concat(TRY(val.hex())));
+  res = TRY(res.concat(">"));
+
+  return res;
 }
 
 Result<String> Writer::write_string(const String& val) {
@@ -427,11 +432,11 @@ Result<String> Writer::write_task_result(const TaskResult& val) {
   String res = TRY(String::create("#<task-result "));
 
   if (error.is<Nil>()) {
-    res = TRY(res.concat(" :result "));
+    res = TRY(res.concat(":result "));
     String s = TRY(write_one(result));
     res = TRY(res.concat(s));
   } else {
-    res = TRY(res.concat(" :error "));
+    res = TRY(res.concat(":error "));
     String s = TRY(write_one(error));
     res = TRY(res.concat(s));
   }
diff --git a/test/continuations.vli b/test/continuations.vli
new file mode 100644
index 0000000..3526feb
--- /dev/null
+++ b/test/continuations.vli
@@ -0,0 +1,4 @@
+(assert (= ((guard (fn () (+ 1 (raise 2)))
+                   (fn (e x) x))
+            2)
+           3))
diff --git a/test/serialize.vli b/test/serialize.vli
new file mode 100644
index 0000000..ebaf238
--- /dev/null
+++ b/test/serialize.vli
@@ -0,0 +1,2 @@
+(assert (= (deserialize (serialize ["foo" "bar" 1]))
+           ["foo" "bar" 1]))