feat(furvm): add step function to executor

furvm/include/furvm/executor.hpp

@@ -9,6 +9,7 @@ namespace furvm {
 
 enum class executor_flags : std::uint32_t {
     Suspended = (1 << 0), /**< Execution suspended. */
+    Done      = (1 << 1), /**< Execution is finished. */
 };
 
 static inline executor_flags operator|(executor_flags lhs, executor_flags rhs) {
@@ -132,6 +133,11 @@ public:
      * @return The thing.
      */
     thing_p thing() const;
+public:
+    /**
+     * @brief Executes next instruction.
+     */
+    void step();
 private:
     executor_handle m_id;
     executor_flags  m_flags{}; // NOLINT(bugprone-invalid-enum-default-initialization)

furvm/include/furvm/fwd.hpp

@@ -75,6 +75,12 @@ using module_handle = std::uint32_t;
  */
 enum class thing_t : std::uint8_t;
 
+/**
+ * @class bad_thing_access
+ * @brief Bad thing access exception.
+ */
+class bad_thing_access;
+
 /**
  * @class thing
  * @brief Furvm thing.

furvm/include/furvm/module.hpp

@@ -42,6 +42,14 @@ public:
      * @return The id.
      */
     constexpr module_handle id() const { return m_id; }
+
+    /**
+     * @brief Returns a byte from bytecode of this module.
+     *
+     * @param offset An offset of the byte.
+     * @return The byte.
+     */
+    constexpr byte byte(std::size_t offset) const { return m_bytecode.at(offset); }
 private:
     module_handle m_id;
     bytecode_t    m_bytecode;

furvm/include/furvm/thing.hpp

@@ -6,7 +6,7 @@
 namespace furvm {
 
 enum class thing_t : std::uint8_t {
-    Int,
+    Int32,
 };
 
 /**
@@ -17,6 +17,39 @@ enum class thing_t : std::uint8_t {
  */
 std::size_t thing_type_size(thing_t type);
 
+class bad_thing_access : public std::exception {
+public:
+    bad_thing_access()           = default;
+    ~bad_thing_access() override = default;
+
+    /**
+     * @brief Move constructor.
+     */
+    bad_thing_access(bad_thing_access&&) noexcept = default;
+
+    /**
+     * @brief Move constructor.
+     */
+    bad_thing_access& operator=(bad_thing_access&&) noexcept = default;
+
+    /**
+     * @brief Copy constructor.
+     */
+    bad_thing_access(const bad_thing_access&) = default;
+
+    /**
+     * @brief Copy constructor.
+     */
+    bad_thing_access& operator=(const bad_thing_access&) = default;
+public:
+    /**
+     * @brief Returns a C-style string describing the cause of the error.
+     *
+     * @return The cause of the error.
+     */
+    const char* what() const noexcept override { return "bad thing access"; }
+};
+
 class thing {
     friend class executor;
 private:
@@ -61,6 +94,20 @@ public:
      * @return Shared pointer to the new thing.
      */
     static thing_p create(const context_p& context, thing_t type);
+public:
+    /**
+     * @brief Returns an int32 value from this thing.
+     *
+     * @return The value.
+     */
+    std::int32_t& int32();
+
+    /**
+     * @brief Returns an int32 value from this thing.
+     *
+     * @return The value.
+     */
+    const std::int32_t& int32() const;
 private:
     thing_handle m_id;
     thing_t      m_type;