I tried it, but it still goes and reads the whole list. Looking at the
`binary` package source code it seems that strict evaluation is hard-coded in
a few places, presumably for performance reasons. It also seems to necessarily
read the bytestring sequentially, so complex tree-like data structures would
presumably encounter problems even if it worked for a list.
Ah well. As long as I'm not duplicating someone else's work, I'm more than
happy to go at this from scratch.
On Wed, 13 Mar 2013, Jeff Shaw wrote:
On 3/13/2013 12:15 AM, Scott Lawrence wrote:
Hey all,
All the object serialization/deserialization libraries I could find (pretty
much just binary and cereal) seem to be strict with respect to the actual
data being serialized. In particular, if I've serialized a large [Int] to a
file, and I want to get the first element, it seems I have no choice but to
deserialize the entire data structure. This is obviously an issue for large
data sets.
There are obvious workarounds (explicitly fetch elements from the
"database" instead of relying on unsafeInterleaveIO to deal with it all
magically), but it seems like it should be possible to build a cereal-like
library that allows proper lazy deserialization. Does it exist, and I've
just missed it?
Thanks,
I haven't tested this, but I suspect something like this could give you lazy
binary serialization and deserialization. It's not tail recursive, though.
newtype LazyBinaryList a = LazyBinaryList [a]
instance Binary a => LazyBinaryList a where
put (LazyBinaryList []) = putWord8 0
put (LazyBinaryList (x:xs)) = putWord8 1 >> put x >> put (LazyBinaryList
xs)
get = do
t <- getWord8
case t of
0 -> return (LazyBinaryList [])
1 -> do
x <- get
(LazyBinaryList xs) <- get
return $ LazyBinaryList (x:xs)
--
Scott Lawrence
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