entrytree_map_maybe :: Entry a => 
    (EntryTree a -> Maybe [EntryTree a] -> Loc -> Maybe [EntryTree a])
    -> [EntryTree a] -> Maybe [EntryTree a]
entrytree_map_maybe f et = entrytree_map_maybe_ f et [0]
entrytree_map_maybe :: Entry a => 
    (EntryTree a -> Maybe [EntryTree a] -> Loc -> Maybe [EntryTree a])
    -> [EntryTree a] -> Maybe [EntryTree a]
entrytree_map_maybe f et = entrytree_map_maybe_ f et [0]
entrytree_map_maybe f et = entrytree_map_maybe_ f et [0]