[Haskell-cafe] Need help with learning Parsec

[Christian Maeder]

Am 19.07.2012 14:53, schrieb C K Kashyap:
> Dear gentle Haskellers,
>
> I was trying to whet my Haskell by trying out Parsec today to try and
> parse out XML. Here's the code I cam up with -
>
> I wanted some help with the "gettext" parser that I've written. I had to
> do a dummy "char '  ') in there just to satisfy the "many" used in the
> xml parser. I'd appreciate it very much if someone could give me some
> feedback.

You don't want empty bodies! So use many1 in gettext.

   gettext = fmap Body $ many1 $ letter <|> digit

If you have spaces in your bodies, skip them or allow them with
noneOf "<".

HTH Christian

>
>
> data XML =  Node String [XML]
>            | Body String deriving Show
>
> gettext = do
>               x <- many (letter <|> digit )
>               if (length x) > 0 then
>                  return (Body x)
>               else (char ' ' >> (return $ Body ""))
>
> xml :: Parser XML
> xml = do {
>            name <- openTag
>          ; innerXML <- many innerXML
>          ; endTag name
>          ; return (Node name innerXML)
>           }
>
> innerXML = do
>           x <- (try xml <|> gettext)
>           return x
>
> openTag :: Parser String
> openTag = do
>          char '<'
>          content <- many (noneOf ">")
>          char '>'
>          return content
>
> endTag :: String -> Parser String
> endTag str = do
>          char '<'
>          char '/'
>          string str
>          char '>'
>          return str
>
> h1 = parse xml "" "<a>A</a>"
> h2 = parse xml "" "<a><b>A</b></a>"
> h3 = parse xml "" "<a><b><c></c></b></a>"
> h4 = parse xml "" "<a><b></b><c></c></a>"
>
> Regards,
> Kashyap
>
>
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