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27 lines
728 B
Haskell
27 lines
728 B
Haskell
module Hledger.Utils.Tree
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( FastTree(..)
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, treeFromPaths
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) where
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-- import Data.Char
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import Data.List (foldl')
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import qualified Data.Map as M
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-- | An efficient-to-build tree suggested by Cale Gibbard, probably
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-- better than accountNameTreeFrom.
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newtype FastTree a = T (M.Map a (FastTree a))
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deriving (Show, Eq, Ord)
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emptyTree :: FastTree a
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emptyTree = T M.empty
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mergeTrees :: (Ord a) => FastTree a -> FastTree a -> FastTree a
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mergeTrees (T m) (T m') = T (M.unionWith mergeTrees m m')
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treeFromPath :: [a] -> FastTree a
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treeFromPath [] = T M.empty
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treeFromPath (x:xs) = T (M.singleton x (treeFromPath xs))
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treeFromPaths :: (Ord a) => [[a]] -> FastTree a
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treeFromPaths = foldl' mergeTrees emptyTree . map treeFromPath
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