struct RNode (NODE) 結構的使用方式可以從 node.h 定義的 macro 裡面猜一下，一組一組的應該對應到不同 node_type，只是沒註解也看不出直接規則。比較好猜的是 nd_lit，應該是 literal 存在 u1.value。

#define nd_head  u1.node
#define nd_alen  u2.argc
#define nd_next  u3.node

#define nd_cond  u1.node
#define nd_body  u2.node
#define nd_else  u3.node

#define nd_resq  u2.node
#define nd_ensr  u3.node

#define nd_1st   u1.node
#define nd_2nd   u2.node

#define nd_stts  u1.node

#define nd_entry u3.id
#define nd_vid   u1.id

#define nd_var   u1.node
#define nd_iter  u3.node

#define nd_value u2.node
#define nd_aid   u3.id

#define nd_lit   u1.value

#define nd_recv  u1.node
#define nd_mid   u2.id
#define nd_args  u3.node
#define nd_ainfo u3.args

#define nd_defn  u3.node

#define nd_cpath u1.node
#define nd_super u3.node

#define nd_beg   u1.node
#define nd_end   u2.node
#define nd_state u3.state

#define nd_nth   u2.argc

#define nd_alias  u1.id
#define nd_orig   u2.id
#define nd_undef  u2.node

#define nd_brace u2.argc

#define nd_pconst     u1.node
#define nd_pkwargs    u2.node
#define nd_pkwrestarg u3.node

#define nd_apinfo u3.apinfo

#define nd_fpinfo u3.fpinfo

// for NODE_SCOPE
#define nd_tbl   u1.tbl

// for NODE_ARGS_AUX
#define nd_pid   u1.id
#define nd_plen  u2.argc
#define nd_cflag u2.id

// for ripper
#define nd_cval  u3.value
#define nd_rval  u2.value
#define nd_tag   u1.id