HaXmlSource codeContentsIndex
Text.XML.HaXml.Combinators
Contents
The content filter type.
Simple filters.
Selection filters.
Predicate filters.
Search filters.
Filter combinators
Basic combinators.
Recursive search.
Interior editing.
Constructive filters.
C-like conditionals.
Filters with labelled results.
Using and combining labelled filters.
Some label-generating filters.
Description

This module defines the notion of filters and filter combinators for processing XML documents.

These XML transformation combinators are described in the paper ``Haskell and XML: Generic Combinators or Type-Based Translation?'' Malcolm Wallace and Colin Runciman, Proceedings ICFP'99.

Synopsis
type CFilter = Content -> [Content]
keep :: a -> [a]
none :: a -> [a]
children :: CFilter
position :: Int -> CFilter -> CFilter
elm :: CFilter
txt :: CFilter
tag :: String -> CFilter
attr :: Name -> CFilter
attrval :: Attribute -> CFilter
tagWith :: (String -> Bool) -> CFilter
find :: String -> (String -> CFilter) -> CFilter
iffind :: String -> (String -> CFilter) -> CFilter -> CFilter
ifTxt :: (String -> CFilter) -> CFilter -> CFilter
o :: CFilter -> CFilter -> CFilter
union :: (a -> [b]) -> (a -> [b]) -> a -> [b]
cat :: [a -> [b]] -> a -> [b]
andThen :: (a -> c) -> (c -> a -> b) -> a -> b
(|>|) :: (a -> [b]) -> (a -> [b]) -> a -> [b]
with :: CFilter -> CFilter -> CFilter
without :: CFilter -> CFilter -> CFilter
(/>) :: CFilter -> CFilter -> CFilter
(</) :: CFilter -> CFilter -> CFilter
et :: (String -> CFilter) -> CFilter -> CFilter
path :: [CFilter] -> CFilter
deep :: CFilter -> CFilter
deepest :: CFilter -> CFilter
multi :: CFilter -> CFilter
when :: CFilter -> CFilter -> CFilter
guards :: CFilter -> CFilter -> CFilter
chip :: CFilter -> CFilter
foldXml :: CFilter -> CFilter
mkElem :: String -> [CFilter] -> CFilter
mkElemAttr :: String -> [(String, CFilter)] -> [CFilter] -> CFilter
literal :: String -> CFilter
cdata :: String -> CFilter
replaceTag :: String -> CFilter
replaceAttrs :: [(String, String)] -> CFilter
data ThenElse a = a :> a
(?>) :: (a -> [b]) -> ThenElse (a -> [b]) -> a -> [b]
type LabelFilter a = Content -> [(a, Content)]
oo :: (a -> CFilter) -> LabelFilter a -> CFilter
x :: (CFilter -> LabelFilter a) -> (CFilter -> LabelFilter b) -> CFilter -> LabelFilter (a, b)
numbered :: CFilter -> LabelFilter String
interspersed :: String -> CFilter -> String -> LabelFilter String
tagged :: CFilter -> LabelFilter String
attributed :: String -> CFilter -> LabelFilter String
textlabelled :: CFilter -> LabelFilter (Maybe String)
extracted :: (Content -> a) -> CFilter -> LabelFilter a
The content filter type.
type CFilter = Content -> [Content]Source
All document transformations are content filters. A filter takes a single XML Content value and returns a sequence of Content values, possibly empty.
Simple filters.
Selection filters.
In the algebra of combinators, none is the zero, and keep the identity. (They have a more general type than just CFilter.)
keep :: a -> [a]Source
none :: a -> [a]Source
children :: CFilterSource
Throw away current node, keep just the (unprocessed) children.
position :: Int -> CFilter -> CFilterSource
Select the n'th positional result of a filter.
Predicate filters.
These filters either keep or throw away some content based on a simple test. For instance, elm keeps only a tagged element, txt keeps only non-element text, tag keeps only an element with the named tag, attr keeps only an element with the named attribute, attrval keeps only an element with the given attribute value, tagWith keeps only an element whose tag name satisfies the given predicate.
elm :: CFilterSource
txt :: CFilterSource
tag :: String -> CFilterSource
attr :: Name -> CFilterSource
attrval :: Attribute -> CFilterSource
tagWith :: (String -> Bool) -> CFilterSource
Search filters.
find :: String -> (String -> CFilter) -> CFilterSource
For a mandatory attribute field, find key cont looks up the value of the attribute name key, and applies the continuation cont to the value.
iffind :: String -> (String -> CFilter) -> CFilter -> CFilterSource
When an attribute field may be absent, use iffind key yes no to lookup its value. If the attribute is absent, it acts as the no filter, otherwise it applies the yes filter.
ifTxt :: (String -> CFilter) -> CFilter -> CFilterSource
ifTxt yes no processes any textual content with the yes filter, but otherwise is the same as the no filter.
Filter combinators
Basic combinators.
o :: CFilter -> CFilter -> CFilterSource
Sequential (Irish,backwards) composition
union :: (a -> [b]) -> (a -> [b]) -> a -> [b]Source
Binary parallel composition. Each filter uses a copy of the input, rather than one filter using the result of the other. (Has a more general type than just CFilter.)
cat :: [a -> [b]] -> a -> [b]Source
Glue a list of filters together. (A list version of union; also has a more general type than just CFilter.)
andThen :: (a -> c) -> (c -> a -> b) -> a -> bSource
A special form of filter composition where the second filter works over the same data as the first, but also uses the first's result.
(|>|) :: (a -> [b]) -> (a -> [b]) -> a -> [b]Source
Directional choice: in f |>| g give g-productions only if no f-productions
with :: CFilter -> CFilter -> CFilterSource
Pruning: in f with g, keep only those f-productions which have at least one g-production
without :: CFilter -> CFilter -> CFilterSource
Pruning: in f without g, keep only those f-productions which have no g-productions
(/>) :: CFilter -> CFilter -> CFilterSource
Pronounced slash, f /> g means g inside f
(</) :: CFilter -> CFilter -> CFilterSource
Pronounced outside, f </ g means f containing g
et :: (String -> CFilter) -> CFilter -> CFilterSource
Join an element-matching filter with a text-only filter
path :: [CFilter] -> CFilterSource
Express a list of filters like an XPath query, e.g. path [children, tag "name1", attr "attr1", children, tag "name2"] is like the XPath query /name1[@attr1]/name2.
Recursive search.
Recursive search has three variants: deep does a breadth-first search of the tree, deepest does a depth-first search, multi returns content at all tree-levels, even those strictly contained within results that have already been returned.
deep :: CFilter -> CFilterSource
deepest :: CFilter -> CFilterSource
multi :: CFilter -> CFilterSource
Interior editing.
when :: CFilter -> CFilter -> CFilterSource
Interior editing: f when g applies f only when the predicate g succeeds, otherwise the content is unchanged.
guards :: CFilter -> CFilter -> CFilterSource
Interior editing: g guards f applies f only when the predicate g succeeds, otherwise the content is discarded.
chip :: CFilter -> CFilterSource
Process CHildren In Place. The filter is applied to any children of an element content, and the element rebuilt around the results.
foldXml :: CFilter -> CFilterSource
Recursive application of filters: a fold-like operator. Defined as f o chip (foldXml f).
Constructive filters.
mkElem :: String -> [CFilter] -> CFilterSource
Build an element with the given tag name - its content is the results of the given list of filters.
mkElemAttr :: String -> [(String, CFilter)] -> [CFilter] -> CFilterSource
Build an element with the given name, attributes, and content.
literal :: String -> CFilterSource
Build some textual content.
cdata :: String -> CFilterSource
Build some CDATA content.
replaceTag :: String -> CFilterSource
Rename an element tag.
replaceAttrs :: [(String, String)] -> CFilterSource
Replace the attributes of an element.
C-like conditionals.

These definitions provide C-like conditionals, lifted to the filter level.

The (cond ? yes : no) style in C becomes (cond ?> yes :> no) in Haskell.

data ThenElse a Source
Conjoin the two branches of a conditional.
Constructors
a :> a
(?>) :: (a -> [b]) -> ThenElse (a -> [b]) -> a -> [b]Source
Select between the two branches of a joined conditional.
Filters with labelled results.
type LabelFilter a = Content -> [(a, Content)]Source
A LabelFilter is like a CFilter except that it pairs up a polymorphic value (label) with each of its results.
Using and combining labelled filters.
oo :: (a -> CFilter) -> LabelFilter a -> CFilterSource
Compose a label-processing filter with a label-generating filter.
x :: (CFilter -> LabelFilter a) -> (CFilter -> LabelFilter b) -> CFilter -> LabelFilter (a, b)Source
Combine labels. Think of this as a pair-wise zip on labels.
Some label-generating filters.
numbered :: CFilter -> LabelFilter StringSource
Number the results from 1 upwards.
interspersed :: String -> CFilter -> String -> LabelFilter StringSource
In interspersed a f b, label each result of f with the string a, except for the last one which is labelled with the string b.
tagged :: CFilter -> LabelFilter StringSource
Label each element in the result with its tag name. Non-element results get an empty string label.
attributed :: String -> CFilter -> LabelFilter StringSource
Label each element in the result with the value of the named attribute. Elements without the attribute, and non-element results, get an empty string label.
textlabelled :: CFilter -> LabelFilter (Maybe String)Source
Label each textual part of the result with its text. Element results get an empty string label.
extracted :: (Content -> a) -> CFilter -> LabelFilter aSource
Label each content with some information extracted from itself.
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