[Haskell-beginners] error writing FilePath to text file

[Michael Snoyman]

On Wed, Jun 29, 2016 at 11:20 AM, Dennis Raddle <dennis.raddle at gmail.com>
wrote:

> Hello, I wrote a program that reads filenames using System.Directory
> "listDirectory", does some tests on them, and writes certain file names (as
> read into a FilePath variable by listDirectory) to a text file, which I
> later parse with Parsec.  I am getting an error on writing to the text file:
>
> commitBuffer: invalid argument (invalid character)
>
> What can I do about this? If I am reading some kind of unusual characters
> from the FilePath, I want to choose some way of writing them so that the
> resulting file can still be parsed by Text.Parsec.ByteString. I hope that I
> can still rely on the "space" parser to find CR and LF, and don't want any
> other surprises.
>
> D
>
>
I'd recommend being explicit about the character encoding you're using, and
using the bytestring API for the I/O itself. As an example:

import qualified Data.Text.Lazy as TL
import qualified Data.Text.Lazy.Encoding as TL
import qualified Data.ByteString.Lazy as L

writeFileUtf8 :: FilePath -> String -> IO ()
writeFileUtf8 fp str = L.writeFile fp (TL.encodeUtf8 (TL.pack str))

The default handling of character encodings is reliant on environment
variables, which IME makes the textual file writing functions notoriously
fragile.

Michael
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