Reading multiple files fails

[Henk-Jan.van.Tuyl]

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)


--
   

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