#pragma once

#include <concepts>
#include <cstdint>
#include <cstring>
#include <iostream>

#include "arena.hpp"
#include "pod.hpp"
#include "utf8.hpp"

// Forward declarations

class Value;
class String;
class Nil;
class Int64;
class Float;
class Bool;
class String;
class Symbol;
class Syntax;
class Pair;
class Array;
class ByteArray;
class Writer;

short cmp_tag(Tag lhs, Tag rhs);

class Object {
 public:
  virtual Tag tag() = 0;
  virtual Result<Value> copy(Arena& arena) = 0;
  virtual PodObject* pod() = 0;
  virtual void move(Object*) = 0;
  virtual ~Object() = default;

  virtual Result<short> cmp(Arena&, Object&) = 0;
  virtual Result<short> cmp(Arena&, Nil&) { return cmp_tag(tag(), Tag::Nil); }
  virtual Result<short> cmp(Arena&, Int64&) {
    return cmp_tag(tag(), Tag::Int64);
  }
  virtual Result<short> cmp(Arena&, Float&) {
    return cmp_tag(tag(), Tag::Float);
  }
  virtual Result<short> cmp(Arena&, Bool&) { return cmp_tag(tag(), Tag::Bool); }
  virtual Result<short> cmp(Arena&, String&) {
    return cmp_tag(tag(), Tag::String);
  }
  virtual Result<short> cmp(Arena&, Symbol&) {
    return cmp_tag(tag(), Tag::Symbol);
  }
  virtual Result<short> cmp(Arena&, Syntax&) {
    return cmp_tag(tag(), Tag::Syntax);
  }
  virtual Result<short> cmp(Arena&, Pair&) { return cmp_tag(tag(), Tag::Pair); }
  virtual Result<short> cmp(Arena&, Array&) {
    return cmp_tag(tag(), Tag::Array);
  }
  virtual Result<short> cmp(Arena&, ByteArray&) {
    return cmp_tag(tag(), Tag::ByteArray);
  }

  Object() = default;
  Object(const Object&) = delete;
};

class Nil : public Object {
 public:
  Nil() {}
  Nil(Nil&& rhs) : _value(std::move(rhs._value)) {}
  Nil(GcRoot<PodNil>&& val) : _value(std::move(val)) {}

  virtual Tag tag() final { return Tag::Nil; }
  virtual PodObject* pod() final { return _value.get(); }

  virtual Result<short> cmp(Arena& arena, Object& rhs) final {
    return -TRY(rhs.cmp(arena, *this));
  }
  virtual Result<short> cmp(Arena&, Nil& rhs) final { return 0; }

  static Result<Nil> create(Arena& arena, PodNil* obj) {
    return Nil(TRY(MkGcRoot(obj, arena)));
  }

  static Result<Nil> create(Arena& arena) {
    auto pod = TRY(arena.alloc<PodNil>());
    pod->header.tag = Tag::Nil;

    return Nil(TRY(MkGcRoot(pod, arena)));
  }

  virtual Result<Value> copy(Arena& arena) final;

  virtual void move(Object* obj) final { new (obj) Nil(std::move(_value)); }

 private:
  GcRoot<PodNil> _value;
};

class Array : public Object {
 public:
  Array() {}
  Array(Array&& rhs) : _value(std::move(rhs._value)) {}
  Array(GcRoot<PodArray>&& val) : _value(std::move(val)) {}

  Array& operator=(Array&& rhs) {
    _value = std::move(rhs._value);
    return *this;
  }

  virtual Tag tag() final { return Tag::Array; }
  virtual PodObject* pod() final { return _value.get(); }
  virtual Result<short> cmp(Arena& arena, Object& rhs) final {
    return -TRY(rhs.cmp(arena, *this));
  }
  virtual Result<short> cmp(Arena&, Array& rhs) final { return 0; }

  virtual void move(Object* obj) final { new (obj) Array(std::move(_value)); }

  static Result<Array> create(Arena& arena, PodArray* obj) {
    return Array(TRY(MkGcRoot(obj, arena)));
  }

  static Result<Array> create(Arena& arena) {
    auto pod = TRY(arena.alloc<PodArray>());
    pod->header.tag = Tag::Array;

    pod->size = 0;

    return Array(TRY(MkGcRoot(pod, arena)));
  }

  uint64_t size() { return _value->size; }
  virtual Result<Value> copy(Arena& arena) final;

  Result<Value> get(Arena& arena, uint64_t idx);

  Result<Array> append(Arena& arena, Value& rhs);

  Result<Array> concat(Arena& arena, Array& rhs) {
    uint64_t rhs_size = rhs.size();
    uint64_t lhs_size = size();
    uint64_t res_size = lhs_size + rhs_size;

    auto pod = TRY(arena.alloc<PodArray>(res_size * sizeof(PodObject*)));
    pod->size = res_size;
    memcpy(pod->data, _value->data, sizeof(PodObject*) * lhs_size);
    memcpy(pod->data + lhs_size, rhs._value->data, sizeof(char) * rhs_size);

    return Array(TRY(MkGcRoot(pod, arena)));
  }

  Result<Array> sub(Arena& arena, uint64_t start, uint64_t end) {
    if (start > end) return ErrorCode::IndexOutOfRange;
    uint64_t res_size = end - start;
    auto pod = TRY(arena.alloc<PodArray>(res_size * sizeof(PodObject*)));
    pod->size = res_size;
    memcpy(pod->data, _value->data + start, sizeof(PodObject*) * res_size);

    return Array(TRY(MkGcRoot(pod, arena)));
  }

 private:
  GcRoot<PodArray> _value;
};

class ByteArray : public Object {
 public:
  ByteArray() {}
  ByteArray(ByteArray&& rhs) : _value(std::move(rhs._value)) {}
  ByteArray(GcRoot<PodByteArray>&& val) : _value(std::move(val)) {}

  ByteArray& operator=(ByteArray&& rhs) {
    _value = std::move(rhs._value);
    return *this;
  }

  virtual Tag tag() final { return Tag::ByteArray; }
  virtual PodObject* pod() final { return _value.get(); }
  virtual Result<short> cmp(Arena& arena, Object& rhs) final {
    return -TRY(rhs.cmp(arena, *this));
  }
  virtual Result<short> cmp(Arena&, ByteArray& rhs) final { return 0; }

  virtual void move(Object* obj) final {
    new (obj) ByteArray(std::move(_value));
  }

  static Result<ByteArray> create(Arena& arena, PodByteArray* obj) {
    return ByteArray(TRY(MkGcRoot(obj, arena)));
  }
  static Result<ByteArray> create(Arena& arena, 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;

    return ByteArray(TRY(MkGcRoot(pod, arena)));
  }

  static Result<ByteArray> create(Arena& arena, 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;

    return ByteArray(TRY(MkGcRoot(pod, arena)));
  }

  static Result<ByteArray> create(Arena& arena, String& str);

  uint64_t size() { return _value->size; }
  virtual Result<Value> copy(Arena& arena) final;

  Result<char> operator[](uint64_t idx) {
    if (idx >= _value->size) return ErrorCode::IndexOutOfRange;
    return _value->data[idx];
  }

  Result<ByteArray> concat(Arena& arena, const char* rhs) {
    uint64_t rhs_size = strlen(rhs);
    uint64_t lhs_size = size();
    uint64_t res_size = lhs_size + rhs_size;

    auto pod = TRY(arena.alloc<PodByteArray>(res_size * sizeof(char)));
    pod->size = res_size;
    memcpy(pod->data, _value->data, sizeof(char) * lhs_size);
    memcpy(pod->data, rhs + lhs_size, sizeof(char) * rhs_size);

    return ByteArray(TRY(MkGcRoot(pod, arena)));
  }

  Result<ByteArray> concat(Arena& arena, const char* rhs, uint64_t rhs_size) {
    uint64_t lhs_size = size();
    uint64_t res_size = lhs_size + rhs_size;

    auto pod = TRY(arena.alloc<PodByteArray>(res_size * sizeof(char)));
    pod->size = res_size;
    memcpy(pod->data, _value->data, sizeof(char) * lhs_size);
    memcpy(pod->data, rhs + lhs_size, sizeof(char) * rhs_size);

    return ByteArray(TRY(MkGcRoot(pod, arena)));
  }

  Result<ByteArray> concat(Arena& arena, ByteArray& rhs) {
    uint64_t rhs_size = rhs.size();
    uint64_t lhs_size = size();
    uint64_t res_size = lhs_size + rhs_size;

    auto pod = TRY(arena.alloc<PodByteArray>(res_size * sizeof(char)));
    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);

    return ByteArray(TRY(MkGcRoot(pod, arena)));
  }

  Result<ByteArray> sub(Arena& arena, uint64_t start, uint64_t end) {
    if (start > end) return ErrorCode::IndexOutOfRange;
    uint64_t res_size = end - start;
    auto pod = TRY(arena.alloc<PodByteArray>(res_size * sizeof(char)));
    pod->size = res_size;
    memcpy(pod->data, _value->data + start, sizeof(char) * res_size);

    return ByteArray(TRY(MkGcRoot(pod, arena)));
  }

 private:
  GcRoot<PodByteArray> _value;
};

class Dict : public Object {
 public:
  friend class Writer;
  Dict() {}
  Dict(Dict&& rhs) : _value(std::move(rhs._value)) {}
  Dict(GcRoot<PodDict>&& val) : _value(std::move(val)) {}

  Dict& operator=(Dict&& rhs) {
    _value = std::move(rhs._value);
    return *this;
  }

  virtual Tag tag() final { return Tag::Dict; }
  virtual PodObject* pod() final { return _value.get(); }
  virtual Result<short> cmp(Arena& arena, Object& rhs) final {
    return -TRY(rhs.cmp(arena, *this));
  }
  virtual Result<short> cmp(Arena&, Dict& rhs) final;

  virtual void move(Object* obj) final { new (obj) Dict(std::move(_value)); }

  static Result<Dict> create(Arena& arena, PodDict* obj) {
    return Dict(TRY(MkGcRoot(obj, arena)));
  }

  static Result<Dict> create(Arena& arena) {
    auto pod = TRY(arena.alloc<PodDict>());
    pod->header.tag = Tag::Dict;

    pod->size = 0;

    return Dict(TRY(MkGcRoot(pod, arena)));
  }

  virtual Result<Value> copy(Arena& arena) final;

  Result<Value> get(Arena& arena, Value& key);

  Result<Dict> insert(Arena& arena, Value& key, Value& value);

  template <class K, class V>
  Result<Dict> insert(Arena& arena, const K& key, const V& value);

  Result<Dict> concat(Arena& arena, Dict& rhs) {
    uint64_t rhs_size = rhs.size();
    uint64_t lhs_size = size();
    uint64_t res_size = lhs_size + rhs_size;

    auto pod = TRY(arena.alloc<PodDict>(res_size * sizeof(PodObject*)));
    pod->size = res_size;
    memcpy(pod->data, _value->data, sizeof(PodObject*) * lhs_size);
    memcpy(pod->data + lhs_size, rhs._value->data, sizeof(char) * rhs_size);

    return Dict(TRY(MkGcRoot(pod, arena)));
  }

 private:
  Result<uint64_t> find(Arena& arena, Value& key);

  uint64_t size() { return _value->size; }
  GcRoot<PodDict> _value;
};

class String : public Object {
 public:
  String() {}
  String(String&& rhs) : _value(std::move(rhs._value)) {}
  String(GcRoot<PodString>&& val) : _value(std::move(val)) {}

  String& operator=(String&& rhs) {
    _value = std::move(rhs._value);
    return *this;
  }

  virtual Tag tag() final { return Tag::String; }
  virtual PodObject* pod() final { return _value.get(); }
  virtual Result<short> cmp(Arena& arena, Object& rhs) final {
    return -TRY(rhs.cmp(arena, *this));
  }
  virtual Result<short> cmp(Arena&, String& rhs) final {
    auto lsize = size();
    auto rsize = rhs.size();
    uint64_t i = 0;
    uint64_t j = 0;
    while (1) {
      if (i == lsize && j == lsize) return 0;

      short cmp = short(i == lsize) - short(j == rsize);
      if (cmp != 0) return cmp;

      char32_t lc = _value->data[i];
      char32_t rc = rhs._value->data[j];
      cmp = (lc > rc) - (lc < rc);
      if (cmp != 0) return cmp;
      i++;
      j++;
    }
    return 0;
  }

  virtual void move(Object* obj) final { new (obj) String(std::move(_value)); }

  static Result<String> create(Arena& arena, PodString* obj) {
    return String(TRY(MkGcRoot(obj, arena)));
  }
  static Result<String> create(Arena& arena, 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;

    return String(TRY(MkGcRoot(pod, arena)));
  }

  static Result<String> create(Arena& arena, 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;

    return String(TRY(MkGcRoot(pod, arena)));
  }

  uint64_t size() { return _value->size; }
  virtual Result<Value> copy(Arena& arena) final;

  Result<char32_t> operator[](uint64_t idx) {
    if (idx >= _value->size) return ErrorCode::IndexOutOfRange;
    return _value->data[idx];
  }

  Result<String> concat(Arena& arena, const char* rhs) {
    uint64_t rhs_size = strlen(rhs);
    uint64_t lhs_size = size();
    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];

    return String(TRY(MkGcRoot(pod, arena)));
  }

  Result<String> concat(Arena& arena, const char32_t* rhs, uint64_t rhs_size) {
    uint64_t lhs_size = size();
    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];

    return String(TRY(MkGcRoot(pod, arena)));
  }

  Result<String> concat(Arena& arena, String& rhs) {
    uint64_t rhs_size = rhs.size();
    uint64_t lhs_size = size();
    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);

    return String(TRY(MkGcRoot(pod, arena)));
  }

  Result<String> sub(Arena& arena, uint64_t start, uint64_t end) {
    if (start > end) return ErrorCode::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);

    return String(TRY(MkGcRoot(pod, arena)));
  }

  friend class Symbol;

 private:
  GcRoot<PodString> _value;
};

class Symbol : public Object {
 public:
  Symbol() {}
  Symbol(Symbol&& rhs) : _value(std::move(rhs._value)) {}
  Symbol(GcRoot<PodSymbol>&& val) : _value(std::move(val)) {}
  virtual Tag tag() final { return Tag::Symbol; }
  virtual PodObject* pod() final { return _value.get(); }
  virtual Result<short> cmp(Arena& arena, Object& rhs) final {
    return -TRY(rhs.cmp(arena, *this));
  }
  virtual Result<short> cmp(Arena&, Symbol& rhs) final { return 0; }

  virtual void move(Object* obj) final { new (obj) Symbol(std::move(_value)); }

  static Result<Symbol> create(Arena& arena, PodSymbol* obj) {
    return Symbol(TRY(MkGcRoot(obj, arena)));
  }

  static Result<Symbol> create(Arena& arena, 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));

    return Symbol(TRY(MkGcRoot(pod, arena)));
  }

  static Result<Symbol> create(Arena& arena, String& rhs);
  virtual Result<Value> copy(Arena& arena) final;

  uint64_t size() { return _value->size; }

  Result<char32_t> operator[](uint64_t idx) {
    if (idx >= _value->size) return ErrorCode::IndexOutOfRange;
    return _value->data[idx];
  }

 private:
  GcRoot<PodSymbol> _value;
};

class Syntax : public Object {
 public:
  Syntax() {}
  Syntax(Syntax&& rhs) : _value(std::move(rhs._value)) {}
  Syntax(GcRoot<PodSyntax>&& val) : _value(std::move(val)) {}
  Syntax(String filename, String modulename, Value expression);
  virtual Tag tag() final { return Tag::Syntax; }
  virtual PodObject* pod() final { return _value.get(); }
  virtual Result<short> cmp(Arena& arena, Object& rhs) final {
    return -TRY(rhs.cmp(arena, *this));
  }
  virtual Result<short> cmp(Arena&, Syntax& rhs) final { return 0; }

  virtual void move(Object* obj) final { new (obj) Syntax(std::move(_value)); }

  static Result<Syntax> create(Arena& arena, PodSyntax* obj) {
    return Syntax(TRY(MkGcRoot(obj, arena)));
  }

  Result<Value> get_value(Arena& arena);

  virtual Result<Value> copy(Arena& arena) final;

 private:
  GcRoot<PodSyntax> _value;
};

class Pair : public Object {
 public:
  Pair() {}
  Pair(Pair&& rhs) : _value(std::move(rhs._value)) {}
  Pair(GcRoot<PodPair>&& val) : _value(std::move(val)) {}
  virtual Tag tag() final { return Tag::Pair; }
  virtual PodObject* pod() final { return _value.get(); }
  virtual Result<short> cmp(Arena& arena, Object& rhs) final {
    return -TRY(rhs.cmp(arena, *this));
  }
  virtual Result<short> cmp(Arena&, Pair& rhs) final { return 0; }

  virtual void move(Object* obj) final { new (obj) Pair(std::move(_value)); }

  static Result<Pair> create(Arena& arena, PodPair* obj) {
    return Pair(TRY(MkGcRoot(obj, arena)));
  }
  static Result<Pair> create(Arena& arena, Value& first, Value& rest);

  Result<Value> first(Arena& arena);
  Result<Value> rest(Arena& arena);

  virtual Result<Value> copy(Arena& arena) final;

 private:
  GcRoot<PodPair> _value;
};

class Int64 : public Object {
 public:
  friend class Float;

  Int64() {}
  Int64(Int64&& rhs) : _value(std::move(rhs._value)) {}
  Int64(GcRoot<PodInt64>&& val) : _value(std::move(val)) {}
  virtual Tag tag() final { return Tag::Int64; }
  virtual PodObject* pod() final { return _value.get(); }
  virtual Result<short> cmp(Arena& arena, Object& rhs) final {
    return -TRY(rhs.cmp(arena, *this));
  }
  virtual Result<short> cmp(Arena&, Int64& rhs) final {
    return (_value->value > rhs._value->value) -
           (_value->value < rhs._value->value);
  }
  virtual Result<short> cmp(Arena&, Float& rhs) final;

  virtual void move(Object* obj) final { new (obj) Int64(std::move(_value)); }

  static Result<Int64> create(Arena& arena, PodInt64* obj) {
    return Int64(TRY(MkGcRoot(obj, arena)));
  }

  static Result<Int64> create(Arena& arena, double val) {
    auto pod = TRY(arena.alloc<PodInt64>());
    pod->header.tag = Tag::Int64;
    pod->value = val;

    return Int64(TRY(MkGcRoot(pod, arena)));
  }

  int64_t value() { return _value->value; }

  virtual Result<Value> copy(Arena& arena) final;

 private:
  GcRoot<PodInt64> _value;
};

class Float : public Object {
 public:
  friend class Int64;

  Float() {}
  Float(Float&& rhs) : _value(std::move(rhs._value)) {}
  Float(GcRoot<PodFloat>&& val) : _value(std::move(val)) {}
  virtual Tag tag() final { return Tag::Float; }
  virtual PodObject* pod() final { return _value.get(); }
  virtual Result<short> cmp(Arena& arena, Object& rhs) final {
    return -TRY(rhs.cmp(arena, *this));
  }
  virtual Result<short> cmp(Arena&, Float& rhs) final {
    return (_value->value > rhs._value->value) -
           (_value->value < rhs._value->value);
  }
  virtual Result<short> cmp(Arena&, Int64& rhs) final;

  virtual void move(Object* obj) final { new (obj) Float(std::move(_value)); }

  static Result<Float> create(Arena& arena, PodFloat* obj) {
    return Float(TRY(MkGcRoot(obj, arena)));
  }

  static Result<Float> create(Arena& arena, double val) {
    auto pod = TRY(arena.alloc<PodFloat>());
    pod->header.tag = Tag::Float;
    pod->value = val;

    return Float(TRY(MkGcRoot(pod, arena)));
  }

  double value() { return _value->value; }

  virtual Result<Value> copy(Arena& arena) final;

 private:
  GcRoot<PodFloat> _value;
};

class Bool : public Object {
 public:
  Bool() {}
  Bool(Bool&& rhs) : _value(std::move(rhs._value)) {}
  Bool(GcRoot<PodBool>&& val) : _value(std::move(val)) {}

  virtual Tag tag() final { return Tag::Bool; }
  virtual PodObject* pod() final { return _value.get(); }
  virtual Result<short> cmp(Arena& arena, Object& rhs) final {
    return -TRY(rhs.cmp(arena, *this));
  }
  virtual Result<short> cmp(Arena&, Bool& rhs) final { return 0; }

  virtual void move(Object* obj) final { new (obj) Bool(std::move(_value)); }

  static Result<Bool> create(Arena& arena, PodBool* obj) {
    return Bool(TRY(MkGcRoot(obj, arena)));
  }

  static Result<Bool> create(Arena& arena, bool val) {
    auto pod = TRY(arena.alloc<PodBool>());
    pod->header.tag = Tag::Bool;
    pod->value = val;

    return Bool(TRY(MkGcRoot(pod, arena)));
  }

  bool value() { return _value->value; }

  virtual Result<Value> copy(Arena& arena) final;

 private:
  GcRoot<PodBool> _value;
};

// note: this class doesn't perform proper destruction of objects in some cases
class Value {
 public:
  Value() { new (buf) Nil(); }
  ~Value() { ((Object*)buf)->~Object(); }
  Value(Value&& val) {
    ((Object*)val.buf)->move((Object*)buf);
    new (val.buf) Nil();
  }
  Value(const Value&) = delete;

  template <class T>
  Value(T&& obj)
    requires std::derived_from<T, Object>
  {
    new (buf) T(std::move(obj));
  }

  Value& operator=(Value&& val) {
    ((Object*)buf)->~Object();
    ((Object*)val.buf)->move((Object*)buf);
    new (val.buf) Nil();
    return *this;
  }

  static Result<Value> create(Arena& arena, PodObject* obj);

  static Result<Value> create(Arena& arena, const int64_t& value) {
    return Value(TRY(Int64::create(arena, value)));
  }

  static Result<Value> create(Arena& arena, const char* value) {
    return Value(TRY(String::create(arena, value)));
  }

  template <class T>
  bool is() {
    return dynamic_cast<T*>((Object*)buf) != nullptr;
  }

  template <class T>
  T* to() {
    return dynamic_cast<T*>((Object*)buf);
  }

  PodObject* pod() { return ((Object*)buf)->pod(); }
  Tag tag() { return ((Object*)buf)->tag(); }

  Object& operator*() { return *(Object*)(buf); }
  Object* operator->() { return (Object*)(buf); }

  Result<short> cmp(Arena& arena, Value& rhs) {
    return ((Object*)buf)->cmp(arena, *(Object*)rhs.buf);
  }

  // TODO: cmp() probably doesn't need arena parameter
  // Result<bool> operator==(Value& rhs) { return TRY(cmp(rhs)) == 0; }
  // Result<bool> operator!=(Value& rhs) { return TRY(cmp(rhs)) != 0; }

  Result<Value> copy(Arena& arena) { return ((Object*)buf)->copy(arena); }

 private:
  uint8_t buf[24];
};

Result<Value> syntax_unwrap(Value& val);

Result<Value> reverse(Arena& arena, Value& val);

Result<void> debug_print(Arena& arena, String& val);
Result<void> debug_print(Arena& arena, Value& val);

template <class K, class V>
Result<Dict> Dict::insert(Arena& arena, const K& key, const V& value) {
  Value k = TRY(Value::create(arena, key));
  Value v = TRY(Value::create(arena, value));

  return insert(arena, k, v);
}