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-rw-r--r--TreeZipperUtils.hs40
1 files changed, 40 insertions, 0 deletions
diff --git a/TreeZipperUtils.hs b/TreeZipperUtils.hs
index b6410a3..0c6dc00 100644
--- a/TreeZipperUtils.hs
+++ b/TreeZipperUtils.hs
@@ -1,5 +1,6 @@
module TreeZipperUtils where
+import Data.Maybe
import Data.Tree
import Data.Tree.Zipper
@@ -10,3 +11,42 @@ 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