[Haskell-beginners] error writing FilePath to text file

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