Given that using asdl_seq currently means casting from void*, we could maybe have a set of macros like asdl_seq_GET that are type specialized (there aren't many of them) and in debug mode they can check that the ->kind attribute is consistent with the specific type that the macro represents. For instance asdl_seq_GET_EXPR will check that the ->kind attribute is consistent with a valid EXPR. It will not catch all problems but it will catch almost all the typical ones in simple sequences.