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 5 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] Data.RefSerialize>str 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 [[5,5],[5,5]] 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 True 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; }
- module Data.Parser
- class Serialize c where
- showSR :: Show a => a -> ST String
- readSR :: Read a => ST a
- rShow :: Serialize c => c -> String
- rRead :: Serialize c => String -> c
- insertVar :: (a -> ST String) -> a -> ST String
- readVar :: Serialize c => ST c -> ST c
- varName :: a -> String
- runR :: ST a -> String -> a
- runW :: ST String -> String
- readHexp :: (Num a, Integral a) => ST a
- showHexp :: (Num a, Integral a) => a -> ST String
Documentation
module Data.Parser
:: ST c | read the content of a expression, must be user defined |
Serialize Bool | |
Serialize Char | |
Serialize Double | |
Serialize Float | |
Serialize Int | |
Serialize Integer | |
Serialize Ordering | |
Serialize String | |
Serialize () | |
Serialize a => Serialize [a] | |
Serialize a => Serialize (Maybe a) | |
(Serialize a, Serialize b) => Serialize (Either a b) | |
(Serialize a, Serialize b) => Serialize (a, b) | |
(Serialize a, Ord a, Serialize b) => Serialize (Map a b) |
showSR :: Show a => a -> ST StringSource
if a is an instance of Show, showSR can be used as the showp method the drawback is that the data inside is not inspected for common references so it is recommended to create your own readp method for your complex data structures
readSR :: Read a => ST aSource
if a is an instance of Read, readSR can be used as the readp method the drawback is that the data inside is not inspected for common references so it is recommended to create your own readp method for your complex data structures
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 in the where section 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