utf8 (haskell-utf8)

Get your UTF-8 IO right on the first try.

Reading files in Haskell is trickier than it could be due to the non-obvious interactions between file encodings and system locale. This library is meant to make it easy once and for all by providing “defaults” that make more sense in the modern world.

See this blog post for more details on why this library need to exists and an explanation of some of the opinionated decisions it is based on.

Use

Step 1: Get it

The library is on Hackage, just add it to the dependencies of your project.

Step 2: Wrap your main

Import withUtf8StdHandles from System.IO.Utf8 and wrap it around your main:

main :: IO ()
main = withUtf8StdHandles $ {- ... your main function ... -}

This will make sure that if your program reads something from stdin or outputs something to stdout/stderr, it will not fail with a runtime error due to encoding issues.

Step 3: Read files using UTF-8

If you are going to read a text file (to be precise, if you are going to open a file in text mode), you’ll probably use withFile, openFile, or readFile. Grab the first two from System.IO.Utf8 or the latter from Data.Text.IO.Utf8.

Note: it is best to import these functions qualified.

Note: there is no System.IO.Utf8.readFile because it’s 2020 and you should not read Strings from files.

All these functions will make sure that the content will be treated as if it was encoded in UTF-8 (it is 2020, what else can it be encoded in?).

If, for some reason, you really need to use withFile/openFile from base, just call hSetEncoding h, where h is your handle and hSetEncoding comes from System.IO.Utf8 for your convenience:

import qualified System.IO as IO
import qualified System.IO.Utf8 as Utf8

doSomethingWithAFile :: IO ()
doSomethingWithAFile = IO.withFile "file.txt" IO.ReadMode $ \h -> do
  Utf8.hSetEncoding h
  {- ... work with the file ... -}

Step 4: Write files using UTF-8

When writing a file either open it using withFile/openFile from System.IO.Utf8 or write to it directly with writeFile from Data.Text.IO.Utf8.

Note: it is best to import these functions qualified.

Note that there is no System.IO.Utf8.writeFile.

If, for some reason, you really need to use withFile/openFile from base, do the same as in the previous step.

Contributing

If you encounter any issues when using this library or have improvement ideas, please open report in issue on GitHub. You are also very welcome to submit pull request, if you feel like doing so.

License

MPL-2.0 © Serokell