I was bored so I ran it through ghci and fixed the small errors I
found, here's the "working" version, I don't really have much of test
data to play with, but it seems to be working with the small examples
I copy-n-pasted from the wiki and the bittorrent website:
import qualified Data.Map as Map
import Data.Map(Map)
import Text.ParserCombinators.Parsec
data Bencode = BEInteger Integer
| BEString String
| BEList [Bencode]
| BEDictionary (Map String Bencode)
deriving (Show, Eq)
number :: Parser Integer
number =
do n_str <- many1 digit
let n = read n_str
return n
beString :: Parser Bencode
beString =
do n <- number
char ':'
str <- count (fromInteger n) anyChar
return (BEString str)
beInt :: Parser Bencode
beInt =
do char 'i'
n <- number
char 'e'
return (BEInteger n)
-- parse any Bencoded value
beParse :: Parser Bencode
beParse = beInt <|> beString <|> beDictionary <|> beList
beList :: Parser Bencode
beList =
do char 'l'
xs <- many beParse -- parse many bencoded values
char 'e'
return (BEList xs)
beDictionary :: Parser Bencode
beDictionary =
do char 'd'
(BEString key) <- beString
val <- beParse
(BEDictionary m) <- beDictionary
<|> do char 'e'
return (BEDictionary Map.empty)
return (BEDictionary (Map.insert key val m))
-- main parser function
parseBencoded :: String -> Maybe [Bencode]
parseBencoded str = case parse (many beParse) "" str of
Left err -> Nothing
Right val -> Just val
/S
On 4/20/05, Sebastian Sylvan <[EMAIL PROTECTED]> wrote:
> Yeah, you probably want the main parser to be "many beParser" and not
> just beParser:
>
> -- main parser function
> parseBencoded :: String -> Maybe [Bencode]
> parseBencode str = case parse (many beParse) "" str of
> Left err -> Nothing
> Right val -> Just val
>
> On 4/20/05, Sebastian Sylvan <[EMAIL PROTECTED]> wrote:
> > On 4/20/05, Tommi Airikka <[EMAIL PROTECTED]> wrote:
> > > Hi!
> > >
> > > I was just wondering if there are any good ways to represent a bencoded
> > > (http://en.wikipedia.org/wiki/Bencoding) message in Haskell? Any
> > > suggestions?
> > >
> >
> > Not that I know of, but it should be very easy to write a parser using
> > the parser library Parsec.
> >
> > You'll need a datatype, something like this:
> >
> > data Bencode = BEInteger Integer |
> > BEString String |
> > BEList [Bencode] |
> > BEDictionary (Data.Map String Bencode)
> > deriving (Show, Eq)
> >
> > Which should be sufficient to represent any Bencoded message (if I
> > didn't make a misstake).
> > Then you could probably use the standard char-parser in parsec to
> > parse it quite easily. Read the docs, they're quite straightforward.
> >
> > I'm a bit rusty but something like this:
> >
> > -- just parse an integer, parsec might have one of these already
> > number :: Parser Integer
> > number =
> > do n_str <- many1 digit -- parse a number
> > let n = read n_str -- convert to an Int
> > return n -- return the number
> >
> > beString :: Parser Bencode
> > beString =
> > do n <- number -- the length prefix
> > char ':' -- now a ':'
> > str <- count n anyChar -- and now n number of letters
> > return (BEString str) -- return the string wrapped up as a
> > BEString
> >
> > beInt :: Parser Bencode
> > beInt =
> > do char 'i'
> > n <- number
> > char 'e'
> > return n
> >
> > -- parse any Bencoded value
> > beParse :: Parser Bencode
> > beParse =
> > do beInt <|> beString <|> beDictionary <|> beList
> >
> > beList :: Parser Bencode
> > beList =
> > do char 'l'
> > xs <- many beParse -- parse many bencoded values
> > char 'e'
> > return (BEList xs)
> >
> > beDictionary :: Parser Bencode
> > beDictionary =
> > do char 'd'
> > key <- beString
> > val <- beParse
> > m <- beDictionary <|> char 'e' >> return Data.Map.empty
> > return (Data.Map.insert key val m)
> >
> > -- main parser function
> > parseBencoded :: String -> Maybe Bencode
> > parseBencode str = case parse beParse "" str of
> > Left err -> Nothing
> > Right val -> Just val
> >
> > Note: This is all untested code that I just scribbled down real quick.
> > There's probably tons of misstakes, but you should get the picture.
> > Read the Parsec docs and then write your own.
> >
> > /S
> > --
> > Sebastian Sylvan
> > +46(0)736-818655
> > UIN: 44640862
> >
>
> --
> Sebastian Sylvan
> +46(0)736-818655
> UIN: 44640862
>
--
Sebastian Sylvan
+46(0)736-818655
UIN: 44640862
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