[Haskell-cafe] Data.Binary.IncrementalGet remake

[Sergey Mironov]

Hello cafe.

Haskell wiki told me about continuation-based parser
Data.Binary.IncrementalGet [1] from binary-strict package. I found the
idea very useful and tried to use it. Original library by Lennart
Kolmodin raises some questions. The lib's main data structures are:

data IResult a = IFailed S String
               | IFinished S a
               | IPartial (B.ByteString -> IResult a)

newtype Get r a = Get { unGet :: S -> (a -> S -> IResult r) -> IResult r }

instance Monad (Get r) where
  return a = Get (\s -> \k -> k a s)
  m >>= k = Get (\s -> \cont -> unGet m s (\a -> \s' -> unGet (k a) s' cont))
  fail err = Get (\s -> const $ IFailed s err)

Here, "S" is parser's state. It works well, but currently doesn't
support lookAhead. I tried to add such function and gave up to do it
having current implementation, but write simpler one instead. Please
see IncrementalGet2.hs (link [2] below). Remake is briefly tested, has
no ghc-specific optimizations, but allows user to peek data from
stream.

What bothering me is the fact that I could actually miss idea (or part
of idea) of the original. If it is so, please let me know :) For
example, what is the point of using separate result type r in original
Get r a?

[1] - Original IncrementalGet lib.
    http://www.haskell.org/haskellwiki/DealingWithBinaryData#Incremental_parsing
[2] - Main file of remake
    https://github.com/ierton/binary-incremental-get2/blob/a9f9afaa0cbc0435a8acea338a31aafaef53fb6e/src/Data/Binary/IncrementalGet2.hs
[3] - whole github project
    https://github.com/ierton/binary-incremental-get2
--
Sergey

sorry for weak English