RefSerialize-0.2.4: Write to and read from Strings maintaining internal memory references



Read, Show and Data.Binary do not check for repeated references to the same address. As a result, the data is duplicated when seri<alized. This is a waste of space in the filesystem and also a waste of serialization time. but the worst consequence is that, when the serialized data is read, it allocates multiple copies for the same object when referenced multiple times. Because multiple referenced data is very typical in a pure language such is Haskell, this means that the resulting data loose the beatiful economy of space and processing time that referential transparency permits.

Here comes a brief tutorial:

runW applies showp, the serialization parser of the instance Int for the RefSerialize class

Data.RefSerialize>let x= 5 :: Int
    Data.RefSerialize>runW $ showp x

every instance of Read and Show is an instance of RefSerialize. for how to construct showp and readp parsers, see the demo.hs

rshowp is derived from showp, it labels the serialized data with a variable name

Data.RefSerialize>runW $ rshowp x
     v8 where {v8= 5; }

Data.RefSerialize>runW $ rshowp [2::Int,3::Int]
     v6 where {v6= [ v9,  v10]; v9= 2; v10= 3; }

while showp does a normal show serialization

Data.RefSerialize>runW $ showp [x,x]
    [5, 5]

rshowp variables are serialized memory references: no piece of data that point to the same addrees is serialized but one time

Data.RefSerialize>runW $ rshowp [x,x]
     v9 where {v6= 5; v9= [ v6, v6]; }

this happens recursively

Data.RefSerialize>let xs= [x,x] in str = runW $ rshowp [xs,xs]
     v8 where {v8= [ v10, v10]; v9= 5; v10= [ v9, v9]; }

the rshowp serialized data is read with rreadp. The showp serialized data is read by readp

Data.RefSerialize>let xss= runR rreadp str :: [[Int]]
    Data.RefSerialize>print xss

this is the deserialized data

the deserialized data keep the references!! pointers are restored! That is the whole point!

Data.RefSerialize>varName xss !! 0 == varName xss !! 1

rShow= runW rshowp
    rRead= runR rreadp

Data.RefSerialize>rShow x
     v11 where {v11= 5; }

In the definition of a referencing parser non referencing parsers can be used and viceversa. Use a referencing parser
    when the piece of data is being referenced many times inside the serialized data.

by default the referencing parser is constructed by:

rshowp= insertVar showp
    rreadp= readVar readp
    but this can be redefined. See for example the instance of [] in RefSerialize.hs

This is an example of a showp parser for a simple data structure.

data S= S Int Int deriving ( Show, Eq)

instance  Serialize S  where
        showp (S x y)= do
                        xs <- rshowp x  -- rshowp parsers can be inside showp parser
                        ys <- rshowp y
                        return $ S ++xs++ ++ys

readp =  do
                        symbol S     -- I included a (almost) complete Parsec for deserialization
                        x <- rreadp
                        y <- rreadp
                        return $ S x y

there is a mix between referencing and no referencing parser here:

Data.RefSerialize>putStrLn $ runW $ showp $ S x x
    S  v23 v23 where {v23= 5; }



class Serialize c whereSource




:: c 
-> ST String

shows the content of a expression, must be defined bu the user



:: ST c

read the content of a expression, must be user defined



:: c 
-> ST String

insert a reference (a variable in the where section). rshowp = insertVar showp -- default definition

rreadp :: ST cSource


rShow :: Serialize c => c -> StringSource

use the rshowp parser to serialize the object rShow c= runW $ rshowp c

rRead :: Serialize c => String -> cSource

deserialize trough the rreadp parser rRead str= runR rreadp $ str

insertVar :: (a -> ST String) -> a -> ST StringSource

insert a variable at this position. The expression value is inserted the where part if it is not already created. If the address of this object being parsed correspond with an address already parsed and it is in the where section, then the same variable name is used runW showp (1::Int) -> 1 runW (insertVar showp) (1::Int) -> v1 where { v1=1} runW (insertVar showp) [(1::Int) ,1] -> [v1.v1] where { v1=1} This is useful when the object is referenced many times

readVar :: Serialize c => ST c -> ST cSource

deserialize a variable serialized with insertVar. Memory references are restored

runR :: ST a -> String -> aSource

deserialize the string with the parser

runW :: ST String -> StringSource

serialize x with the parser

readHexp :: (Num a, Integral a) => ST aSource

showHexp :: (Num a, Integral a) => a -> ST StringSource