Add function evaluation

src/special.c

@@ -27,15 +27,7 @@ struct ucl_object *ucl_special_let(struct ucl_state *state, struct ucl_object *a
         ucl_state_put(let_state, sym->symbol, value);
     }
 
-    struct ucl_object *result = NULL;
-    FOREACH_LIST(expressions, iter, item) {
-        result = ucl_evaluate(let_state, item);
-        if (result->type == UCL_TYPE_ERROR) {
-            return result;
-        }
-    }
-
-
+    struct ucl_object *result = ucl_progn(state, expressions);
     ucl_state_delete(let_state);
     return result;
 }