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module TreeZipperUtils where
import Data.Maybe
import Data.Tree
import Data.Tree.Zipper
-- Return loc (as parent-like structure) and parents.
path :: TreePos Full a -> [(Forest a, a, Forest a)]
path loc = toParent loc : parents loc
-- Return parent stack compatible form of loc.
toParent :: TreePos Full a -> (Forest a, a, Forest a)
toParent loc = (before loc, label loc, after loc)
modifyFirstParentLabelWhere
:: (a -> Bool)
-> (a -> a)
-> TreePos Full a
-> TreePos Full a
modifyFirstParentLabelWhere p f loc0 =
case parent loc0 of
Nothing -> loc0
Just loc0' -> go (byChildIndex loc0) loc0'
where
go rewind loc =
if p (label loc)
then
rewind (modifyLabel f loc)
else
case parent loc of
Nothing -> rewind loc
Just loc' ->
go (rewind . byChildIndex loc) loc'
-- generator for a rewind step
byChildIndex :: TreePos Full a -> (TreePos Full a -> TreePos Full a)
byChildIndex loc =
-- The use of fromJust is safe here because we're only modifying
-- labels and not the tree structure and thus the index is valid.
fromJust . childAt (childIndex loc)
-- XXX This could be named more general, like countPrevSiblings?
-- XXX Can we kill the recursion?
childIndex :: TreePos Full a -> Int
childIndex =
go 0
where
go index =
maybe index (go $ index + 1) . prev
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