Thanks Stephen, On Tue, Nov 9, 2010 at 2:53 PM, Stephen Tetley wrote:

I'd use a parser combinator library that has word8 word16, word32 combinators. The latter should really have big and little endian versions word16be, word16le, word32be, word32le.

Data.Binary should provide this and Attoparsec I think. Usually I roll my own, but only because I had my own libraries before these two existed.

The idiom of a tag byte telling you what comes next is very common in binary formats. It means parsers can avoid backtracking altogether.

I'll take a look at attoparsec I was also trying to understand how I could do it myself also - Basically I've been using the Get Monad for getting out the word/8/16 etc out of a ByteStream - but I dont want to write a separate parsing routine for each command. So instead of doing something like this - parseCommand1 byteStream = runGet $ do b1 <- getWord8 b2 <- getWord16be return (b1,b2) parseCommand2 byteStream = runGet $ do b1 <- getWord16be b2 <- getWord16be return (b1,b2) I'd like to do this parse byteStream command = runGet $ do map (commandFormat command) --- or something like this - not exactly sure about this. Regards, Kashyap

I think I can restate my problem like this --- If I have a list of actions as follows - import Data.Word import Data.Binary.Get data MyAction = A1 (Get Word8) | A2 (Get Word16) a = A1 getWord8 b = A2 getWord16be listOfActions = [a,b,a] How can I execute the "listOfActions" inside of a Get Monad and get the output as a list?

On Tue, Nov 9, 2010 at 8:10 AM, C K Kashyap wrote: ] I think I can restate my problem like this --- ] ] If I have a list of actions as follows - ] ] import Data.Word ] import Data.Binary.Get ] ] data MyAction = A1 (Get Word8) | A2 (Get Word16) ] ] a = A1 getWord8 ] b = A2 getWord16be ] ] listOfActions = [a,b,a] ] ] How can I execute the "listOfActions" inside of a Get Monad and get ] the output as a list? Do you mean, something like this?

import Control.Applicative ((<$>))

data MyAction m = A1 (m Word8) | A2 (m Word16)

a = A1 getWord8 b = A2 getWord16be

listOfActions = [a,b,a]

newtype Id a = Id a

getAction :: MyAction Get -> Get (MyAction Id) getAction (A1 act) = A1 . Id <$> act getAction (A2 act) = A2 . Id <$> act

getActions :: [MyAction Get] -> Get [MyAction Id] getActions = mapM getAction

-- Felipe.

Hi Felipe, On Tue, Nov 9, 2010 at 3:53 PM, Felipe Almeida Lessa wrote:

On Tue, Nov 9, 2010 at 8:10 AM, C K Kashyap wrote: ] I think I can restate my problem like this --- ] ] If I have a list of actions as follows - ] ] import Data.Word ] import Data.Binary.Get ] ] data MyAction = A1 (Get Word8) | A2 (Get Word16) ] ] a = A1 getWord8 ] b = A2 getWord16be ] ] listOfActions = [a,b,a] ] ] How can I execute the "listOfActions" inside of a Get Monad and get ] the output as a list?

Do you mean, something like this?

...

import Control.Applicative ((<$>))

data MyAction m = A1 (m Word8) | A2 (m Word16)

a = A1 getWord8 b = A2 getWord16be

listOfActions = [a,b,a]

newtype Id a = Id a

getAction :: MyAction Get -> Get (MyAction Id) getAction (A1 act) = A1 . Id <$> act getAction (A2 act) = A2 . Id <$> act

getActions :: [MyAction Get] -> Get [MyAction Id] getActions = mapM getAction

-- Felipe.

Could you please give a solution for Put as well ... I need to generate a series of put actions from a list of tuples as follows - [(100,1),(200,2),500,4)] -> [putWord8 100, putWord16be 200, putWord32be 500] -- Regards, Kashyap

2010/11/9 Ozgur Akgun :

If we change the code a bit,

data MyAction = A1 Word8 | A2 Word16

a,b :: Get MyAction

a = A1 <$> getWord8

b = A2 <$> getWord16be

listOfActions :: [Get MyAction] listOfActions = [a,b,a] Now, we know how to execute the list of actions, and get the output as list. Using the following guys: sequence :: Monad m => [m a] -> m [a] runGet :: Get a -> ByteString -> a

The original question was (I believe) how to drive the parsing with a list of Actions, not the result be a list of Actions. Cheers, Thu

Thanks Ozgur and Felipe, Could you also show how I could actually use it to parse a bytestring please? import qualified Data.ByteString.Lazy as BS import Control.Applicative ((<$>)) import Data.Word import Data.Binary.Get data MyAction = A1 Word8 | A2 Word16 a,b :: Get MyAction a = A1 <$> getWord8 b = A2 <$> getWord16be listOfActions :: [Get MyAction] listOfActions = [a,b,a] --sequence :: Monad m => [m a] -> m [a] --runGet :: Get a -> ByteString -> a bs = BS.pack [1,0,2] How exactly can I get back a list of integers from bs? -- Regards, Kashyap