[Haskell-cafe] Data.Binary.IncrementalGet remake

[Antoine Latter]

On Wed, Apr 20, 2011 at 1:03 PM, Sergey Mironov <ierton at gmail.com> wrote:
> 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:
>

Lennart Kolmodin has a branch of Binary with incremental get which
supports lookAhead:

https://github.com/kolmodin/binary/tree/cps

I don't have performance measurements, but if you look-ahead too far
it obviously isn't good for memory consumption.

Antoine

> 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
>
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