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-- Modify foldTree to allow the caller to change the order of traversal of
-- entries in a directory.
{-- From examples/examples/ch09/FoldDir.hs modified according to the assignment
--
-- Added missing import of takeBaseName.
--}
import ControlledVisit (Info(..), getInfo, getUsefulContents, isDirectory)
import Control.Monad (liftM)
import Data.Char (toLower)
import System.FilePath ((</>), takeFileName, takeExtension, takeBaseName)
data Iterate seed = Done { unwrap :: seed }
| Skip { unwrap :: seed }
| Continue { unwrap :: seed }
deriving (Show)
type Iterator seed = seed -> Info -> Iterate seed
foldTree :: Iterator a -> a -> FilePath -> ([FilePath] -> IO [FilePath]) -> IO a
foldTree iter initSeed path order = do
endSeed <- fold initSeed path
return (unwrap endSeed)
where
fold seed subpath = getUsefulContents subpath >>= order >>= walk seed
walk seed (name:names) = do
let path' = path </> name
info <- getInfo path'
case iter seed info of
done@(Done _) -> return done
Skip seed' -> walk seed' names
Continue seed'
| isDirectory info -> do
next <- fold seed' path'
case next of
done@(Done _) -> return done
seed'' -> walk (unwrap seed'') names
| otherwise -> walk seed' names
walk seed _ = return (Continue seed)
{-- End of code from examples --}
orderId :: [FilePath] -> IO [FilePath]
orderId fs = return fs
orderReverse :: [FilePath] -> IO [FilePath]
orderReverse fs = return (reverse fs)
-- Helper iterator that returns the traversed files for easy observing of
-- effects of the order functions.
allPaths :: Iterator [FilePath]
allPaths paths info = Continue ((infoPath info) : paths)
-- ghci> :l 9_c_1.hs
-- [1 of 2] Compiling ControlledVisit ( ControlledVisit.hs, interpreted )
-- [2 of 2] Compiling Main ( 9_c_1.hs, interpreted )
-- Ok, two modules loaded.
-- ghci> foldTree allPaths [] "test-9_b_4/" orderId
-- ["test-9_b_4/C.c","test-9_b_4/E.hs","test-9_b_4/D.hs","test-9_b_4/B.c","test-9_b_4/A.c","test-9_b_4/F.hs"]
-- ghci> foldTree allPaths [] "test-9_b_4/" orderReverse
-- ["test-9_b_4/F.hs","test-9_b_4/A.c","test-9_b_4/B.c","test-9_b_4/D.hs","test-9_b_4/E.hs","test-9_b_4/C.c"]
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