[Haskell] Simple and Easy Persistence

[Donald Bruce Stewart]

I usually use the the Binary class, found in NewBinary for this task.
You derive Binary for each type you wish to serialise, which gives you a
get and put function on handles. A stripped down version suitable for
many tasks lives here:
    http://www.cse.unsw.edu.au/~dons/code/hmp3/Binary.hs

This is the same class GHC uses to read and write .hi files.
Some info on this at http://www.haskell.org/hawiki/BinaryIo, and 
ftp://ftp.cs.york.ac.uk/pub/malcolm/ismm98.html

Examples of a persistent database here:
    http://www.cse.unsw.edu.au/~dons/code/hmp3/Tree.hs
and here 
    http://www.cse.unsw.edu.au/~dons/code/lambdabot/Plugins/Seen.hs

I actually think a derivable class Binary is simple and solid enough it
should be in the standard libs..

-- Don

mmm92:
> Hi all,
> 
>   I have some program data that I'd like to persist.  I could just  
> use read and show and file I/O to store arrays as files. [1]  This  
> works and it is easy and simple (which I like) but it is also  
> inefficient and a little cumbersome.
> 
>   I imagine that this is a very common task, and I know of utilities  
> in other environments like object databases, embedded databases, XML  
> persistence, etc. that can make this kind of persistence simple *and*  
> relatively efficient and reliable.  E.g.) I have found the HSQLDB  
> embedded database [2] to be useful when writing Java applications.   
> What do you do for quick and easy persistence in Haskell?  Are there  
> any libraries or techniques that are especially useful for this?
> 
> [1]
> > type SimpleRecord = (Integer, Integer, Integer)
> > type SimpleIndex = Integer
> > type SimpleDB = (Array SimpleIndex SimpleRecord, FilePath)
> 
> > loadDB :: FilePath -> IO SimpleDB
> > loadDB f = do h <- openFile f ReadMode
> >               s <- hGetContents h
> >               hClose h
> >               return $ r s
> >  where r :: String -> SimpleDB
> >        r = read
> 
> > getRecord :: SimpleDB -> SimpleIndex -> SimpleRecord
> > getRecord (a, _) = (a !)
> 
> > updateRecord :: SimpleDB -> SimpleIndex -> SimpleRecord -> SimpleDB
> > updateRecord (a, f) i r = (a//[(i,r)],f)
> 
> > storeDB :: SimpleDB -> IO ()
> > storeDB sdb@(a,f) = do h <- openFile f WriteMode
> >                        hPutStr h (show sdb)
> >                        hClose h
> 
> > sampleDB = (array (0,10) [(x,(x+1,x*2,42)) | x <- [0..10]],"output/ 
> 1.db.txt")
> 
> [2] http://hsqldb.org/
> 
>   - Matt Munz
>     mmm92 at pantheon.yale.edu
> 
> 
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