[Haskell-cafe] Polymorphic functions over string libraries

[gonzaw]

Hi.

I was wondering what would be the best way to create a polymorphic function
over any possible string library (Text, String, Bytestring, etc).

For instance, imagine I have to read a file with text, transform this text
in some way and output it to another file, or to the console.
If I wanted to use String, I'd just do this:
/
transform :: String -> String
main = readFile "input.txt" >>= writeFile "output.txt" . transform
/
But if I wanted to use Text instead, I'd have to use this:
/
import qualified Data.Text.IO as T

transform :: Text -> Text
main = T.readFile "input.txt" >>= T.writeFile "output.txt" . transform
/
Idem for ByteString.

I was wondering if there was a way to create these computations in a generic
way, for any kind of string library, something like this:
/
class StringLibrary s where:
sReadFile :: FilePath -> IO s
sWriteFile :: FilePath -> s -> IO ()
...
/
So then I'd just have this:
/
transform :: StringLibrary s => s -> s
main = sReadFile "input.txt" >>= sWriteFile "output.txt" . transform
/
Now I can perform the computation I want without being tied down to a
specific library. At times when I create some quick scripts, I find myself
using one library (for example using String to get it finished more quickly,
since I have less experience with the other ones), but find that it's too
slow or has some problem that is solved by using one of the other libraries.
Yet swapping from one to the other is more cumbersome than expected at
times.
In the example above, I could easily swap between them, just by forcing the
compiler to typecheck to a specific one (for instance by changing the type
of "transform"). Or if I wanted to, I could leave it as it is and export it
as a library of my own.

Is there a way to do something like this in Haskell, with existing
libraries?
In terms of using the string datatype as some sort of container of
characters, I think there are libraries like Lens and mono-traversable that
allow you to do stuff like this. But I'm not too familiar with them (at
least using them in this way).




--
View this message in context: http://haskell.1045720.n5.nabble.com/Polymorphic-functions-over-string-libraries-tp5758630.html
Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.