Reading POT files in Haskell using Attoparsec

Question

I have a set of POT files that I want to read in order to postprocess translations in Haskell. Due to the POT files being very large, I want to use attoparsec to get a good performance.

I tried using hgettext, but my task is not to read translations for translating my program but merely to parse the POT files. Basically, I want to get a list of (comment, msgid, msgstr) tuples

Answer 1

Assuming the POT file to read is stored in mypot.pot, you can use this code which you can directly run in runghc. I have tested this successfully using some Khan Academy PO files, but it currently only works with simple files (no plural etc), but it is easy to extend:

{-# LANGUAGE OverloadedStrings #-}

import Prelude hiding (takeWhile)
import Data.Attoparsec.ByteString
import Data.Attoparsec.ByteString.Char8 hiding (takeWhile, skipWhile)
import qualified Data.Text.Encoding as TE
import Data.Text(Text)
import Data.Word
import Data.ByteString (unsnoc, ByteString)
import qualified Data.ByteString.Char8 as B
import Control.Applicative
import Control.Monad
import Data.Maybe
import Data.Either
import qualified Data.Text as T

data PORecord = PORecord {
        poComment :: Text,
        poMsgid :: Text,
        poMsgstr :: Text
    } deriving (Show, Eq)

takeTillEOL :: Parser ByteString
takeTillEOL = takeWhile (not . isEndOfLine)

parseMsgidMsgstrLine :: ByteString -> Parser Text
parseMsgidMsgstrLine key = do
  void (string key) <?> "Line key"
  skipSpace
  char '"' <?> "Opening Qutotation mark"
  val <- takeTillEOL
  endOfLine <?> "EOL"
  return $ TE.decodeUtf8 $ fromMaybe "" $ (fst <$> unsnoc val)

msgidLine = parseMsgidMsgstrLine "msgid"
msgstrLine = parseMsgidMsgstrLine "msgstr"

escapedTextLine :: Parser Text
escapedTextLine = char '"' *> (TE.decodeUtf8 <$> takeTillEOL) <* endOfLine
--escapedTextLine = do
--    char '"'
--    val <- takeTillEOL
--    return $ (traceShow val ())

nameP :: String -> Parser a -> Parser a
nameP str p = p <?> str

commentLine :: Parser Text
commentLine = nameP "comment line" $ do
    char '#' <?> "Line start hash"
    -- Skip space but not newline
    void $ many (char ' ')
    txt <- TE.decodeUtf8 <$> takeTillEOL
    endOfLine <?> "EOF"
    return txt

emptyLine :: Parser ()
emptyLine = skipSpace <* endOfLine

poRecord :: Parser PORecord
poRecord = do
    comments <- many1 commentLine <?> "Comments"
    msgidPrimary <- msgidLine <?> "msgid"
    extraMsgid <- many escapedTextLine <?> "Extra msgid"
    msgstrPrimary <- msgstrLine <?> "msgstr"
    extraMsgstr <- many escapedTextLine <?> "Extra msgstr"
    endOfLine
    let comment = T.intercalate "\n" comments
    let msgid = T.intercalate "\n" $ msgidPrimary : extraMsgid
    let msgstr = T.intercalate "\n" $ msgstrPrimary : extraMsgstr
    return $ PORecord comment msgid msgstr

poFile :: Parser [PORecord]
poFile =
    --let options = choice [emptyLine *> pure Nothing, ]
    many1 poRecord <?> "PO results"

main :: IO ()
main = do
    f <- B.readFile "mypot.pot"
    print $ parseOnly poFile f