aggstate_set_extra ElemType period_agg SKIPLIST_GROW skiplist_headval SKIPLIST_INITIAL_CAPACITY SKIPLIST_INITIAL_FREELIST skiplist_make SKIPLIST_MAXLEVEL skiplist_splice skiplist_values tagg_deserialize tagg_serialize timestamp_agg tinstant_tagg tsequence_tagg

skiplist_headval() void* skiplist_headval ( SkipList *  list ) Returns the value at the head of the skiplist.