[Haskell-cafe] What other prelude to cleanly convert text-files into json

Bram Neijt bneijt at gmail.com
Sun Mar 1 16:47:22 UTC 2015

Thank you all for the responses.

Qualified imports for a script of less then a page make the code less
readable. That is why I want to specifically import subsets of
functions and not prefix everything with qualified imports.

I've taken the code from Travis (clean up some of the useless
pack/unpack), decided to use "NoImplicitPrelude" and then I had this:

{-# LANGUAGE NoImplicitPrelude, OverloadedStrings #-}
import Prelude (Show, IO, (++), print, String, filter)
import Data.List (isSuffixOf)
import Data.Text hiding (isSuffixOf, filter)
import Data.Text.IO
import Control.Monad (mapM_)

import qualified Data.ByteString.Lazy as BL
import System.Directory (getDirectoryContents)
import System.FilePath.Posix ((<.>), FilePath, takeBaseName)

import Data.Aeson

data Product = Product
    { image :: Text
    , description  :: Text
    } deriving Show

instance ToJSON Product where
    toJSON (Product image description) = object ["image" .= image,
"description" .= description]

encodeToJson :: FilePath -> IO()
encodeToJson srcName = do
    let jsonName = takeBaseName srcName <.> "json"
    contents <- readFile srcName
    let contentLines = lines contents
    case contentLines of  -- head is unsafe!  try your code on an empty file
      (firstLine : restLines) -> BL.writeFile jsonName (encode Product {
            image = firstLine,
            description = unlines restLines
      _ -> print ("error: invalid source file: " ++ srcName)

main = do
    names <- getDirectoryContents "."
    let srcNames = filter (isSuffixOf ".src") names
    mapM_ encodeToJson srcNames

What bugs me is that this is a really simple thing to do in any other
language, but here I seem to be stuck between Prelude and Text and as
a beginner Prelude is king.

I tried ClassyPrelude but got stuck at not being able to get the
result of getDirectoryContents into the ClassyPrelude version of
mapM_. Sorry but I gave up on that.

I think that given all this, the above code is as beautiful as Haskell
can pull this off at the moment.

If somebody can prove me wrong, I would love to still see it.



On Sun, Mar 1, 2015 at 1:42 AM, Travis Cardwell
<travis.cardwell at extellisys.com> wrote:
> On 2015年02月28日 20:23, Bram Neijt wrote:
>> It quickly became a collection of "import qualified" and "T.unpack,
>> T.pack" calls that made the whole thing look ugly [1].
> <SNIP>
>> [1] Source can be read here: https://gist.github.com/bneijt/9bdb4b1759790a8463c9
> File paths are of type `System.FilePath.Posix.FilePath`, a type alias for
> `String`.  Note that this convention is also followed in `ByteString` and
> `Text` libraries; they do not use `ByteString` or `Text` types for the
> file paths.
> In this code, file paths are packed only to have to unpack them again
> (twice!), which likely offsets any performance improvements of using the
> `Text` version of `isSuffixOf`.
> Here is a version using the same style but without packing file paths:
> https://gist.github.com/TravisCardwell/fd9981e4968e4af3751d
> I included a few other changes, which are commented in the code.
> By the way, I do not think that qualified imports are bad.  I like them
> because they provide an explicit reference to the source module of a function.
> Cheers,
> Travis
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe at haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe

More information about the Haskell-Cafe mailing list