feat: introduce AST type class

Refs: #15

furc/include/furc/ast/declaration.hpp

@@ -5,10 +5,25 @@
 #include "furc/ast/statement.hpp"
 
 #include <string>
+#include <type_traits>
 
 namespace furc {
 namespace ast {
 
+/**
+ * @brief Type class for AST declarations.
+ */
+class type {
+public:
+    template <typename NameFwd, typename = std::enable_if_t<std::is_constructible_v<std::string, NameFwd>>>
+    type(NameFwd&& name)
+      : m_name(std::forward<NameFwd>(name)) {}
+public:
+    const std::string& name() const { return m_name; }
+private:
+    std::string m_name;
+};
+
 /**
  * @brief Declaration node type.
  */

furc/include/furc/ast/fwd.hpp

@@ -71,6 +71,10 @@ using expression_node_p = node_p<expression_node>; /**< Alias for a shared point
 
 using expression_node_r = node_r<expression_node>; /**< Alias for expression_node result */
 
+class type;
+
+using type_r = furlang::result<type, error>; /**< Alias for AST type result */
+
 class declaration_node;
 
 using declaration_node_p = node_p<declaration_node>; /**< Alias for a shared pointer to declaration_node. */