feat(furc): introduce native and import functions

Closes: #19

furc/include/furc/ast/declaration.hpp

@@ -79,6 +79,12 @@ struct function_declaration_param {
     type        type;
 };
 
+enum class function_declaration_node_t {
+    Normal = 0,
+    Import,
+    Native,
+};
+
 /**
  * @brief Function declaration AST node.
  */
@@ -92,11 +98,16 @@ public:
      * @param type Return type of the function.
      */
     template <typename T, typename ParamsFwd>
-    function_declaration_node(struct location location, T&& name, std::optional<type>&& returnType, ParamsFwd&& params)
+    function_declaration_node(struct location location,
+        T&&                                   name,
+        std::optional<type>&&                 returnType,
+        ParamsFwd&&                           params,
+        function_declaration_node_t           type = function_declaration_node_t::Normal)
       : declaration_node(location),
         p_name(std::forward<T>(name)),
         p_returnType(std::move(returnType)),
-        p_params(std::forward<ParamsFwd>(params)) {}
+        p_params(std::forward<ParamsFwd>(params)),
+        p_type(type) {}
 public:
     /**
      * @brief Returns this node's declaration type.
@@ -125,6 +136,13 @@ public:
      * @return Function's parameters.
      */
     const std::vector<function_declaration_param>& params() const { return p_params; }
+
+    /**
+     * @brief Returns function's type.
+     *
+     * @return Function's type.
+     */
+    function_declaration_node_t type() const { return p_type; }
 public:
     void accept(visitor& visitor) const override;
 
@@ -140,12 +158,17 @@ protected:
     /**
      * @brief Return type of the function.
      */
-    std::optional<type> p_returnType;
+    std::optional<class type> p_returnType;
 
     /**
      * @brief Parameters of the function.
      */
     std::vector<function_declaration_param> p_params;
+
+    /**
+     * @brief Type of the function declaration.
+     */
+    function_declaration_node_t p_type;
 };
 
 /**
@@ -164,7 +187,7 @@ public:
     template <typename T, typename ParamsFwd>
     function_definition_node(struct location location,
         T&&                                  name,
-        std::optional<type>&&                type,
+        std::optional<class type>&&          type,
         ParamsFwd&&                          params,
         body&&                               body)
       : function_declaration_node(location, std::forward<T>(name), std::move(type), std::forward<ParamsFwd>(params)),

furc/include/furc/front/token.hpp

@@ -153,6 +153,8 @@ enum class keyword_token {
     If,     /**< `if` */
     Else,   /**< `else` */
     While,  /**< `while` */
+    Import, /**< `import` */
+    Native, /**< `native` */
 
     Int32, /**< `int32` */
 };
@@ -165,6 +167,8 @@ static inline std::ostream& operator<<(std::ostream& os, keyword_token keyword)
     case keyword_token::If: return os << "if";
     case keyword_token::Else: return os << "else";
     case keyword_token::While: return os << "while";
+    case keyword_token::Import: return os << "import";
+    case keyword_token::Native: return os << "native";
     case keyword_token::Int32: return os << "int32";
     }
     return os;
@@ -178,6 +182,8 @@ static inline std::string operator+(const std::string& str, keyword_token keywor
     case keyword_token::If: return str + "if";
     case keyword_token::Else: return str + "else";
     case keyword_token::While: return str + "while";
+    case keyword_token::Import: return str + "import";
+    case keyword_token::Native: return str + "native";
     case keyword_token::Int32: return str + "int32";
     }
     return str;