turning Strings into Text in Haskell

Question

Using the Haskell d3.js library I am trying to make a bar chart a bar chart.

 import Control.Monad
 import qualified Data.Text as T
 import D3JS

 test :: Int -> IO ()
 test n = T.writeFile "generated.js" $ reify (box "#div1" (300,300) >>= bars n 300 (Data1D [100,20,80,60,120]))

Even with this simple example I have a number of questions.

• import qualified seems to require namespaces. Then instead of Data.Text.writeFile we can write T.writeFile
• Data.Text.writeFile does not appear listed in hackage's entry on Data.Text but I did find it in relation to prelude.

Here is an example of a simple T.writeFile error:

> import qualified Data.Text.IO as T
> T.writeFile "helloWorld.txt" "Hello World!"

Couldn't match expected type ‘Text’ with actual type ‘String’

Hopefully all of this type-casting can be sorted out. Then I have big question about how reify works. For now... how do I even changed the String to a Text here?

Answer 1

Use Data.Text.pack to convert a String into Text:

pack :: String -> Text

Also, the Text version of writeFile appears in Data.Text.IO, e.g.:

import qualified Data.Text.IO as T

T.writeFile "helloWorld.txt" (T.pack "Hello World!")

It's ok to import both Data.Text and Data.Text.IO as T.

Answer 2

In addition to the conversion functions mentioned, you might want to use the {-# LANGUAGE OverloadedStrings #-} pragma at the top of your file to enable tho OverloadedStrings extension, which lets you write string literals, but automatically converting them to a compatible type (say Text).

Read more at https://ocharles.org.uk/blog/posts/2014-12-17-overloaded-strings.html.