> The following code runs out of file handles, so I am seeking
> enlightenment as to why.
>
> > -- | add data from a file to the histogram
> > addFile :: FiniteMap String Int -> String -> IO (FiniteMap
> String Int)
> > addFile fm name = do
> > x <- readFile name
> > return (addHist fm x)
> >
> > -- | add data from all files in a directory to the histogram
> > addDir :: FiniteMap String Int -> String -> IO (FiniteMap
> String Int)
> > addDir fm dir = do
> > dc <- getDirectoryContents dir
> > fs <- filterM doesFileExist (map ((dir++"/")++) dc)
> > foldM addFile fm fs
>
> Running addDir on a directory with few hundred files trigs it.
> Shouldn't all of each file's contents be consumed by each addFile, and
> thus the handle be released?
It's not possible to tell from this code whether the readFiles will be
fully evaluated or not: it depends on how much evaluation addHist does,
and to what extend the result FiniteMap is demanded, amongst other
things.
These things are always tricky to understand, which is why I recommend
not using lazy I/O. File reading is not a pure operation: running out
of file descriptors is a good counter-example.
Cheers,
Simon
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