feat(furc/parser): add pre- and post- conditions

furc/include/furc/front/ast.hpp

@@ -116,10 +116,16 @@ struct var_decl_node final : public decl_node {
 struct func_decl_node final : public decl_node {
     decl_type_e decl_type() const override { return Function; }
 
-    std::string                   name;
-    ast_type                      type;
-    std::vector<var_decl_node>    params;
-    std::optional<comp_stmt_node> body;
+    struct def_s {
+        comp_stmt_node          body;
+        std::vector<expr_node*> preConds;
+        std::vector<expr_node*> postConds;
+    };
+
+    std::string                name;
+    ast_type                   type;
+    std::vector<var_decl_node> params;
+    std::optional<def_s>       def;
 };
 
 class expr_node : public stmt_node {

furc/include/furc/front/token.hpp

@@ -76,6 +76,8 @@ struct token {
         While,   /**< `while` */
         Public,  /**< `public` */
         Private, /**< `private` */
+        Pre,     /**< `pre` */
+        Post,    /**< `post` */
 
         Pointerof, /**< `pointerof` */
         Sizeof,    /**< `sizeof` */
@@ -186,6 +188,8 @@ struct token {
         case token::While: return os << "while";
         case token::Public: return os << "public";
         case token::Private: return os << "private";
+        case token::Pre: return os << "pre";
+        case token::Post: return os << "post";
         case token::Pointerof: return os << "pointerof";
         case token::Sizeof: return os << "sizeof";
         case token::Lengthof: return os << "lengthof";