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Haskell Quiz/GEDCOM/Solution Abhinav

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-- A GEDCOM to XML converter written using Parsec as a
-- solution for rubyquiz 6 (http://rubyquiz.com/quiz6.html).
-- Example GEDCOM document at
-- http://cpansearch.perl.org/src/PJCJ/Gedcom-1.16/royal.ged
 
{-# LANGUAGE NoMonomorphismRestriction, RecordWildCards #-}
 
module GedcomParser where
 
import Text.Parsec hiding (spaces, Line)
import System.IO
 
-- a line in a GEDCOM document
data Line = Line {
                lineLevel :: Int,
                lineTag :: String,
                lineValue :: Maybe String,
                lineId :: Maybe String
            } deriving (Show)
 
-- an element in a GEDCOM document
data Elem = Elem {
                elemTag :: String,
                elemValue :: Maybe String,
                elemId :: Maybe String,
                elemChildren :: [Elem]
            } deriving (Show)
 
indent n = concat . (replicate n) $ "  "
 
trimValue value = case value of
    Nothing -> Nothing
    Just v
        | v == "" -> Nothing
        | otherwise -> Just v
 
normalizeValue = maybe "" id
 
spaces = many (char ' ' <|> tab)
whitespaces = many (char ' ' <|> tab <|> newline)
 
-- parses a line
line level = do
    string (show level)
    spaces
    id <- optionMaybe $ between (char '@') (char '@') (many1 alphaNum)
    spaces
    tag <- many1 upper
    spaces
    value <- fmap trimValue $ optionMaybe $ manyTill (anyChar) newline
    return $ Line level tag value id
 
-- parses an element
element level = do
    ml <- optionMaybe $ line level
    case ml of
        Nothing -> fail ("invalid level " ++ show level)
        Just Line{..} -> do
            children <- many (element $ level + 1)
            return $ Elem lineTag lineValue lineId children
 
-- parses a document
document = (element 0) `endBy` whitespaces
 
-- normalizes an element by merging values of CONC and CONT
-- elements with parent element value
normalizeElem element =
    let
        conChildren = filter concOrCont $ elemChildren element
        text = foldl (\t el -> t
                        ++ (if elemTag el == "CONC" then "\n" else " ")
                        ++ normalizeValue (elemValue el))
                    "" conChildren
        nonConChildren = filter (not . concOrCont) $ elemChildren element
    in
        element { elemValue = trimValue $
                        Just (normalizeValue (elemValue element) ++ text),
                  elemChildren = map normalizeElem nonConChildren }
    where
        concOrCont el = elemTag el `elem` ["CONC", "CONT"]
 
-- normalizes a document
normalizeDoc = map normalizeElem
 
-- converts an element to XML
elemToXml indentation Elem{..} =
    indent indentation
    ++ "<" ++ elemTag
    ++ maybe "" (\i -> " id=\"@" ++ i ++ "@\"") elemId
    ++ case elemChildren of
        [] -> ">" ++ normalizeValue elemValue ++ "</" ++ elemTag ++ ">"
        _ -> maybe "" (\v -> " value=\"" ++ v ++ "\"") elemValue ++ ">\n"
            ++ unlines (map (elemToXml (indentation + 1)) elemChildren)
            ++ indent indentation ++ "</" ++ elemTag ++ ">"
 
-- converts a document to XML
documentToXml doc = "<DOCUMENT>\n"
    ++ (unlines . map (elemToXml 1) $ doc)
    ++ "</DOCUMENT>"
 
-- converts a GEDCOM document supplied through STDIN into XML
-- and prints to STDOUT
main = do
    text <- getContents
    case parse document "GEDCOM Parser" text of
        Right []  -> return ()
        Right doc -> putStrLn $ documentToXml (normalizeDoc doc)
        Left e    -> print e

Description: This solution uses Parsec to parse a GEDCOM file and then converts the parsed data to XML.

Source: https://github.com/abhin4v/rubyquiz/blob/master/GedcomParser.hs