cyclic struct definitions

ast.c

typedef struct _ast_binop_t {
  ast_node_t *left;
  ast_node_t *right;
} ast_binop_t;

typedef union _ast_data_t {
  int integer;
  ast_node_t node;
  char *id;
  ast_binop_t binop;
} ast_data_t;

typedef struct _ast_node_t {
  int type;
  ast_data_t data;
} ast_node_t;

Does this work? Nope

typedef struct _ast_binop_t {
  struct ast_node_t *left;
  struct ast_node_t *right;
} ast_binop_t;

typedef union _ast_data_t {
  int integer;
  struct ast_node_t node;
  char *id;
  struct ast_binop_t binop;
} ast_data_t;

typedef struct _ast_node_t {
  int type;
  struct ast_data_t data;
} ast_node_t;