我希望能写一个Haskell程序来解析一个大约14GB的文本文件,但我不知道如何使其释放未使用的内存,也不知道如何避免在foldr期间出现堆栈溢出。下面是程序源代码:
import qualified Data.ByteString.Lazy.Char8 as LBS
import qualified Data.ByteString.Lex.Lazy.Double as BD
import System.Environment
data Vertex =
Vertex{
vertexX :: Double,
vertexY :: Double,
vertexZ :: Double}
deriving (Eq, Show, Read)
data Extent =
Extent{
extentMax :: Vertex,
extentMin :: Vertex}
deriving (Eq, Show, Read)
addToExtent :: Extent -> Vertex -> Extent
addToExtent ext vert = Extent vertMax vertMin where
(vertMin, vertMax) = (makeCmpVert max (extentMax ext) vert, makeCmpVert min (extentMin ext) vert) where
makeCmpVert f v1 v2 = Vertex(f (vertexX v1) (vertexX v2))
(f (vertexY v1) (vertexY v2))
(f (vertexZ v1) (vertexZ v2))
readCoord :: LBS.ByteString -> Double
readCoord l = case BD.readDouble l of
Nothing -> 0
Just (value, _) -> value
readCoords :: LBS.ByteString -> [Double]
readCoords l | LBS.length l == 0 = []
| otherwise = let coordWords = LBS.split ' ' l
in map readCoord coordWords
parseLine :: LBS.ByteString -> Vertex
parseLine line = Vertex (head coords) (coords!!1) (coords!!2) where
coords = readCoords line
processLines :: [LBS.ByteString] -> Extent -> Extent
processLines strs ext = foldr (\x y -> addToExtent y (parseLine x)) ext strs
processFile :: String -> IO()
processFile name = do
putStrLn name
content <- LBS.readFile name
let (countLine:recordsLines) = LBS.lines content
case LBS.readInt countLine of
Nothing -> putStrLn "Can't read records count"
Just (recordsCount, _) -> do
print recordsCount
let vert = parseLine (head recordsLines)
let ext = Extent vert vert
print $ processLines recordsLines ext
main :: IO()
main = do
args <- getArgs
case args of
[] -> do
putStrLn "Missing file path"
xs -> do
processFile (head xs)
return()
文本文件包含用空格字符分隔的三个浮点数的行。该程序总是试图占用计算机上的所有空闲内存,并因内存不足错误而崩溃。
addToExtent
中犯了一个错误,请查看我的答案中添加的注释。 - Daniel Fischer