ba_append
| '(' vargs ',' expr ')'{ $$ = ba_new(ba_append($2, $4), B_AT_TUPLE); }
| vargs ',' expr { $$ = ba_append($1, $3); }
| GVAR ',' expr { $$ = ba_append(bg_find($1), $3); }
return ba_new(ba_append(da0, da1), op);
struct bt_arg *ba_append(struct bt_arg *, struct bt_arg *);
extern struct bt_arg *ba_append(struct bt_arg *, struct bt_arg *);
bh = ba_append(bh, baeval(ba, dtev));