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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 String
s 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
,
or you got your file handle from somewhere else, wrap the code that works
with it in a call to hWithEncoding
from System.IO.Utf8
:
import qualified System.IO as IO
import qualified System.IO.Utf8 as Utf8
doSomethingWithAFile :: IO.Handle -> IO ()
doSomethingWithAFile h = Utf8.hWithEncoding h $ do
{- ... 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.