At 13:48 12/04/05 +0100, Malcolm Wallace wrote:
Henning Thielemann <[EMAIL PROTECTED]> writes:
> >> predicates a -> Bool > >> selectors, transformators a -> a > >> list-valued functions a -> [a] > > What about providing combinators for the most common cases and provide > lifting functions for the uncommon cases, such as > > liftPred :: (a -> Bool) -> (a -> [a]) > liftPred p x = if p x then [x] else [] > > liftTrans :: (a -> b) -> (a -> [b]) > liftTrans f x = [f x]
Looks good. If you want to come up with a concrete design for an fuller set of alternative combinators, I'd be happy to include it into HaXml as a further choice of facility.
Obliquely related to this thread:
When I added namespace support and other stuff to HaXml, I added (a) and "infoset" type parameter to the XML document type [1], and (b) a new transformation type [2] so that I could create new document types with additional information in the Haskell data to support features like XML namesspaces and xml:base.
I think your proposals could also be added into this framework, with the additional wrinkle that using a 'newtype' in the "infoset" value type, one could maybe achieve a degree of type safety, but at the cost of losing some of the algebraic properties of a 'CFilter'.
My version is on my web site (sorry I'm offline and can't find the actual URI right now).
#g --
[1] From my version of Text.XML.HaXml.Types: [[ data DocumentI i = Document Prolog (SymTab EntityDef) (ElementI i)
data ElementI i = Elem QName i [Attribute] [ContentI i]
data ElemTag = ElemTag Name [Attribute] -- ^ intermediate for parsing
type Attribute = (QName, AttValue)
data ContentI i = CElem (ElementI i)
| CString Bool CharData -- Bool flags whitespace significance
| CRef Reference
| CMisc Misc
| CErr String -- Fudge to get error diagnostics
-- from a filterdata ElementInfoset = EI
{ eiNamespaces :: [Namespace]
, eiBase :: String
-- Non-infoset values
-- (in xml namespace: http://www.w3.org/XML/1998/namespace)
, eiLang :: String
, eiSpace :: Bool -- True=preserve, False=default
-- ? , eiIdent :: String -- xml:id, or other ID value?
} deriving Show
]]
So that:[[ type Document = DocumentI () type Element = ElementI () type Content = ContentI () ]]
Provide compatibility with existing HaXml, but I can use [[ DocumentI ElementInfoset ElementI ElementInfoset ContentI ElementInfoset ]]
...
[2] From my version of Text.XML.HaXml.Combinators: [[ type CTransform i1 i2 = ContentI i1 -> [ContentI i2] type CFilterI i = CTransform i i type CFilter = CFilterI () ]]
------------ Graham Klyne For email: http://www.ninebynine.org/#Contact
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