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Description | ||||||||||||
Version : $Id$ Pickler functions for converting between user defined data types and XmlTree data. Usefull for persistent storage and retreival of arbitray data as XML documents This module is an adaptation of the pickler combinators developed by Andrew Kennedy ( http://research.microsoft.com/~akenn/fun/picklercombinators.pdf ) The difference to Kennedys approach is that the target is not a list of Chars but a list of XmlTrees. The basic picklers will convert data into XML text nodes. New are the picklers for creating elements and attributes. One extension was neccessary: The unpickling may fail. Therefore the unpickler has a Maybe result type. Failure is used to unpickle optional elements (Maybe data) and lists of arbitray length There is an example program demonstrating the use of the picklers for a none trivial data structure. (see "examples/arrows/pickle" directory) | ||||||||||||
Synopsis | ||||||||||||
Documentation | ||||||||||||
xpickleDocument :: PU a -> Attributes -> String -> IOStateArrow s a XmlTree | ||||||||||||
store an arbitray value in a persistent XML document The pickler converts a value into an XML tree, this is written out with Text.XML.HXT.Arrow.writeDocument. The option list is passed to Text.XML.HXT.Arrow.writeDocument An options evaluated by this arrow is a_addDTD. If a_addDTD is set (v_1), the pickler DTD is added as an inline DTD into the document. | ||||||||||||
xunpickleDocument :: PU a -> Attributes -> String -> IOStateArrow s b a | ||||||||||||
read an arbitray value from an XML document The document is read with Text.XML.HXT.Arrow.readDocument. Options are passed to Text.XML.HXT.Arrow.readDocument. The conversion from XmlTree is done with the pickler. xpickleDocument xp al dest >>> xunpickleDocument xp al' dest is the identity arrow when applied with the appropriate options. When during pickling indentation is switched on, the whitespace must be removed during unpickling. | ||||||||||||
xpickleWriteDTD :: PU b -> Attributes -> String -> IOStateArrow s b XmlTree | ||||||||||||
Write out the DTD generated out of a pickler. Calls xpicklerDTD | ||||||||||||
xpickleDTD :: PU b -> IOStateArrow s b XmlTree | ||||||||||||
The arrow for generating the DTD out of a pickler A DTD is generated from a pickler and check for consistency. Errors concerning the DTD are issued. | ||||||||||||
checkPickler :: Eq a => PU a -> IOStateArrow s a a | ||||||||||||
An arrow for checking picklers A value is transformed into an XML document by a given pickler, the associated DTD is extracted from the pickler and checked, the document including the DTD is tranlated into a string, this string is read and validated against the included DTD, and unpickled. The last step is the equality with the input. If the check succeeds, the arrow works like this, else it fails. | ||||||||||||
xpickleVal :: ArrowXml a => PU b -> a b XmlTree | ||||||||||||
The arrow version of the pickler function | ||||||||||||
xunpickleVal :: ArrowXml a => PU b -> a XmlTree b | ||||||||||||
The arrow version of the unpickler function | ||||||||||||
thePicklerDTD :: PU b -> XmlTrees | ||||||||||||
Compute the associated DTD of a pickler | ||||||||||||
a_addDTD :: String | ||||||||||||
Option for generating and adding DTD when document is pickled | ||||||||||||
pickleDoc :: PU a -> a -> XmlTree | ||||||||||||
conversion of an arbitrary value into an XML document tree. The pickler, first parameter, controls the conversion process. Result is a complete document tree including a root node | ||||||||||||
unpickleDoc :: PU a -> XmlTree -> Maybe a | ||||||||||||
Conversion of an XML document tree into an arbitrary data type The inverse of pickleDoc. This law should hold for all picklers: unpickle px . pickle px $ v == Just v . Not every possible combination of picklers make sense. For reconverting a value from an XML tree, is becomes neccessary, to introduce "enough" markup for unpickling the value | ||||||||||||
data PU a | ||||||||||||
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class XmlPickler a where | ||||||||||||
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xp4Tuple :: PU a -> PU b -> PU c -> PU d -> PU (a, b, c, d) | ||||||||||||
Like xpPair and xpTriple but for 4-tuples | ||||||||||||
xp5Tuple :: PU a -> PU b -> PU c -> PU d -> PU e -> PU (a, b, c, d, e) | ||||||||||||
Like xpPair and xpTriple but for 5-tuples | ||||||||||||
xpAddFixedAttr :: String -> String -> PU a -> PU a | ||||||||||||
Add an attribute with a fixed value. Useful e.g. to declare namespaces. Is implemented by xpAttrFixed | ||||||||||||
xpAlt :: (a -> Int) -> [PU a] -> PU a | ||||||||||||
Pickler for sum data types. Every constructor is mapped to an index into the list of picklers. The index is used only during pickling, not during unpickling, there the 1. match is taken | ||||||||||||
xpAttr :: String -> PU a -> PU a | ||||||||||||
Pickler for storing/retreiving data into/from an attribute value The attribute is inserted in the surrounding element constructed by the xpElem pickler | ||||||||||||
xpAttrFixed :: String -> String -> PU () | ||||||||||||
xpAttrImplied :: String -> PU a -> PU (Maybe a) | ||||||||||||
Add an optional attribute for an optional value (Maybe a). | ||||||||||||
xpChoice :: PU b -> PU a -> (a -> PU b) -> PU b | ||||||||||||
combine tow picklers with a choice Run two picklers in sequence like with xpSeq. When during unpickling the first one fails, an alternative pickler (first argument) is applied. This pickler only is used as combinator for unpickling. | ||||||||||||
xpCondSeq :: PU b -> (b -> a) -> PU a -> (a -> PU b) -> PU b | ||||||||||||
pickle/unpickle combinator for sequence and choice. When the first unpickler fails, the second one is taken, else the third one configured with the result from the first is taken. This pickler is a generalisation for xpSeq and xpChoice . The schema must be attached later, e.g. in xpPair or other higher level combinators | ||||||||||||
xpElem :: String -> PU a -> PU a | ||||||||||||
Pickler for wrapping/unwrapping data into an XML element Extra parameter is the element name. THE pickler for constructing nested structures | ||||||||||||
xpickle :: XmlPickler a => PU a | ||||||||||||
xpLift :: a -> PU a | ||||||||||||
Lift a value to a pickler When pickling, nothing is encoded, when unpickling, the given value is inserted. This pickler always succeeds. | ||||||||||||
xpLiftMaybe :: Maybe a -> PU a | ||||||||||||
Lift a Maybe value to a pickler. Nothing is mapped to the zero pickler, Just x is pickled with xpLift x. | ||||||||||||
xpList :: PU a -> PU [a] | ||||||||||||
Encoding of list values by pickling all list elements sequentially. Unpickler relies on failure for detecting the end of the list. The standard pickler for lists. Can also be used in combination with xpWrap for constructing set and map picklers | ||||||||||||
xpList1 :: PU a -> PU [a] | ||||||||||||
Encoding of a none empty list of values Attention: when calling this pickler with an empty list, an internal error "head of empty list is raised". | ||||||||||||
xpOption :: PU a -> PU (Maybe a) | ||||||||||||
Encoding of optional data by ignoring the Nothing case during pickling and relying on failure during unpickling to recompute the Nothing case The default pickler for Maybe types | ||||||||||||
xpPair :: PU a -> PU b -> PU (a, b) | ||||||||||||
pickle a pair of values sequentially Used for pairs or together with wrap for pickling algebraic data types with two components | ||||||||||||
xpPrim :: (Read a, Show a) => PU a | ||||||||||||
Pickle an arbitrary value by applyling show during pickling and read during unpickling. Real pickling is then done with xpString. One of the most often used pimitive picklers. Applicable for all types which are instances of Read and Show | ||||||||||||
xpSeq :: (b -> a) -> PU a -> (a -> PU b) -> PU b | ||||||||||||
Combine two picklers sequentially. If the first fails during unpickling, the whole unpickler fails | ||||||||||||
xpText :: PU String | ||||||||||||
Pickle a string into an XML text node One of the most often used primitive picklers. Attention: For pickling empty strings use xpText0. If the text has a more specific datatype than xsd:string, use xpTextDT | ||||||||||||
xpText0 :: PU String | ||||||||||||
Pickle a possibly empty string into an XML node. Must be used in all places, where empty strings are legal values. If the content of an element can be an empty string, this string disapears during storing the DOM into a document and reparse the document. So the empty text node becomes nothing, and the pickler must deliver an empty string, if there is no text node in the document. | ||||||||||||
xpTextDT :: Schema -> PU String | ||||||||||||
Pickle a string into an XML text node Text pickler with a description of the structure of the text by a schema. A schema for a data type can be defined by scDT. In Text.XML.HXT.Arrow.Pickle.Schema there are some more functions for creating simple datatype descriptions. | ||||||||||||
xpText0DT :: Schema -> PU String | ||||||||||||
Pickle a possibly empty string with a datatype description into an XML node. Like xpText0 but with extra Parameter for datatype description as in xpTextDT. | ||||||||||||
xpTree :: PU XmlTree | ||||||||||||
Pickle an XmlTree by just adding it Usefull for components of type XmlTree in other data structures | ||||||||||||
xpTriple :: PU a -> PU b -> PU c -> PU (a, b, c) | ||||||||||||
Like xpPair but for triples | ||||||||||||
xpUnit :: PU () | ||||||||||||
xpWrap :: (a -> b, b -> a) -> PU a -> PU b | ||||||||||||
map value into another domain and apply pickler there One of the most often used picklers. | ||||||||||||
xpWrapMaybe :: (a -> Maybe b, b -> a) -> PU a -> PU b | ||||||||||||
like xpWrap, but if the inverse mapping is undefined, the unpickler fails Map a value into another domain. If the inverse mapping is undefined (Nothing), the unpickler fails | ||||||||||||
xpZero :: PU a | ||||||||||||
The zero pickler Encodes nothing, fails always during unpickling | ||||||||||||
data Schema | ||||||||||||
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type Schemas = [Schema] | ||||||||||||
data DataTypeDescr | ||||||||||||
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Produced by Haddock version 2.1.0 |