L.S.,
After reading through 60 or 61 files (about 220 kB), Hugs fails with the message:
(1426170 reductions, 2976893 cells, 68 garbage collections)
ERROR - Garbage collection fails to reclaim sufficient space
This is done with the program below (ReadALot.lhs), which reads a series of files (these files are listed in dir.dat).
The program reads the first and the last (non-empty) line of each file and writes them, together with the filename in
the output file result.dat.
The program works fine when compiled with GHC, it then reads 2946 files without a problem.
More info.:
System: Windows 98
Hugs version: Nov 2002
Best regards,
Henk-Jan van Tuyl
======================================================================
ReadALot.lhs
Read a lot of files
2003-10-06
History:
031009 Added dummy parameter to "main"
======================================================================
import IO
import Monad
inputSet :: String
inputSet = "dir.dat"
outputFile :: String
outputFile = "result.dat"
======================================================================
main
======================================================================
main :: a -> IO ()
main _ = do hInputSet <- openFile inputSet ReadMode
hOutputFile <- openFile outputFile WriteMode
fileNames <- hGetContents hInputSet
allData <- collectAllData $ lines fileNames hPutStrLn hOutputFile $ unlines allData hClose hInputSet
hClose hOutputFile
======================================================================
collectAllData
Read a list of file names and return file name, first line and last
line of each file in a list
======================================================================
collectAllData :: [String] -> -- A list of filenames
IO [String] -- A list of results
collectAllData [] = return []
collectAllData (fileName : fileNames) = do
putStrLn $ "Reading: " ++ fileName
h <- openFile fileName ReadMode
contents <- hGetContents h
dataFromFile <- return $! parseFile $ filter (/= "") $ lines
contents let (firstLine, lastLine) = dataFromFile
To force reading of the file before closing, we add a "when" (from
the Monad library), with a boolean expression that uses lastLine
and will always be true:
when (length lastLine >= 0) $
hClose h
rest <- collectAllData fileNames
return $ fileName : firstLine : lastLine : "" : rest
======================================================================
parseFile
Returns the first and the last string of a list of strings, as a tuple
======================================================================
parseFile :: [String] -> (String, String)
parseFile [] = ("", "")
parseFile [x] = (x, "")
parseFile (x : xs) = (x, last xs)
--
