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+module Much.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