Optimize list appends O(n^2)->O(n)

src/evaluate.c

@@ -12,11 +12,12 @@
 struct ucl_object *ucl_evaluate_builtin_form(struct ucl_scope *scope, struct ucl_object *list) {
     // TODO: Reasonably split builtin and non-builtin evaluation
     struct ucl_object *evaluated_list = ucl_nil_create();
+    struct ucl_object *evaluated_list_tail = evaluated_list;
 
     FOREACH_LIST(list, iter, item) {
         struct ucl_object *obj = ucl_evaluate(scope, item);
         UCL_RET_IF_ERROR(obj);
-        ucl_list_append(evaluated_list, obj);
+        evaluated_list_tail = ucl_list_append(evaluated_list_tail, obj);
     };
 
     struct ucl_object *fun = ucl_car(evaluated_list);

src/parse.c

@@ -95,11 +95,12 @@ struct ucl_object *ucl_token_next(const char **curr_src) {
 
 struct ucl_object *ucl_tokenize(const char *source) {
     struct ucl_object *tokens = ucl_nil_create();
+    struct ucl_object *tokens_tail = tokens;
     struct ucl_object *curr_token = NULL;
     const char *curr_src = source;
 
     while ((curr_token = ucl_token_next(&curr_src)) != NULL) {
-        ucl_list_append(tokens, curr_token);
+        tokens_tail = ucl_list_append(tokens_tail, curr_token);
     }
 
     return tokens;
@@ -209,7 +210,7 @@ struct ucl_object *ucl_parse_tokens(struct ucl_object *tokens) {
             return new_sexp;
         }
 
-        ucl_list_append(result_tail, new_sexp);
+        result_tail = ucl_list_append(result_tail, new_sexp);
     }
 
     return result;

src/utility.c

@@ -116,7 +116,7 @@ struct ucl_object *ucl_list_append(struct ucl_object *list, struct ucl_object *o
 
     if (list->cell.car == NULL) {
         list->cell.car = obj;
-        return NULL;
+        return list;
     }
 
     while (iter->cell.cdr != NULL) {