hxt-7.5: A collection of tools for processing XML with Haskell.ContentsIndex
Control.Arrow.ArrowTree
Portabilityportable
Stabilityexperimental
MaintainerUwe Schmidt (uwe\@fh-wedel.de)
Description

Version : $Id: ArrowTree.hs,v 1.12 20061130 16:05:24 hxml Exp $

List arrows for tree processing.

Trees that implement the Data.Tree.Class interface, can be processed with these arrows.

Synopsis
class (ArrowPlus a, ArrowIf a) => ArrowTree a where
getChildren :: Tree t => a (t b) (t b)
getNode :: Tree t => a (t b) b
setChildren :: Tree t => [t b] -> a (t b) (t b)
setNode :: Tree t => b -> a (t b) (t b)
changeChildren :: Tree t => ([t b] -> [t b]) -> a (t b) (t b)
changeNode :: Tree t => (b -> b) -> a (t b) (t b)
processChildren :: Tree t => a (t b) (t b) -> a (t b) (t b)
replaceChildren :: Tree t => a (t b) (t b) -> a (t b) (t b)
(/>) :: Tree t => a (t b) (t b) -> a (t b) (t b) -> a (t b) (t b)
(</) :: Tree t => a (t b) (t b) -> a (t b) (t b) -> a (t b) (t b)
deep :: Tree t => a (t b) (t b) -> a (t b) (t b)
deepest :: Tree t => a (t b) (t b) -> a (t b) (t b)
multi :: Tree t => a (t b) c -> a (t b) c
processBottomUp :: Tree t => a (t b) (t b) -> a (t b) (t b)
processTopDown :: Tree t => a (t b) (t b) -> a (t b) (t b)
processBottomUpWhenNot :: Tree t => a (t b) (t b) -> a (t b) (t b) -> a (t b) (t b)
processTopDownUntil :: Tree t => a (t b) (t b) -> a (t b) (t b)
insertChildrenAt :: Tree t => Int -> a (t b) (t b) -> a (t b) (t b)
insertChildrenAfter :: Tree t => a (t b) (t b) -> a (t b) (t b) -> a (t b) (t b)
insertTreeTemplate :: Tree t => a (t b) (t b) -> [IfThen (a (t b) c) (a (t b) (t b))] -> a (t b) (t b)
class Tree t
Documentation
class (ArrowPlus a, ArrowIf a) => ArrowTree a where

The interface for tree arrows

all functions have default implementations

Methods
getChildren :: Tree t => a (t b) (t b)
select the children of the root of a tree
getNode :: Tree t => a (t b) b
select the attribute of the root of a tree
setChildren :: Tree t => [t b] -> a (t b) (t b)
substitute the children of the root of a tree
setNode :: Tree t => b -> a (t b) (t b)
substitute the attribute of the root of a tree
changeChildren :: Tree t => ([t b] -> [t b]) -> a (t b) (t b)
edit the children of the root of a tree
changeNode :: Tree t => (b -> b) -> a (t b) (t b)
edit the attribute of the root of a tree
processChildren :: Tree t => a (t b) (t b) -> a (t b) (t b)

apply an arrow element wise to all children of the root of a tree collect these results and substitute the children with this result

example: processChildren isText deletes all subtrees, for which isText does not hold

example: processChildren (none `when` isCmt) removes all children, for which isCmt holds

replaceChildren :: Tree t => a (t b) (t b) -> a (t b) (t b)

similar to processChildren, but the new children are computed by processing the whole input tree

example: replaceChildren (deep isText) selects all subtrees for which isText holds and substitutes the children component of the root node with this list

(/>) :: Tree t => a (t b) (t b) -> a (t b) (t b) -> a (t b) (t b)

pronounced "slash", meaning g inside f

defined as f /> g = f >>> getChildren >>> g

example: hasName "html" /> hasName "body" /> hasName "h1"

This expression selects all "h1" elements in the "body" element of an "html" element, an expression, that corresponds 1-1 to the XPath selection path "html/body/h1"

(</) :: Tree t => a (t b) (t b) -> a (t b) (t b) -> a (t b) (t b)

pronounced "outside" meaning f containing g

defined as f </ g = f `containing` (getChildren >>> g)

deep :: Tree t => a (t b) (t b) -> a (t b) (t b)

recursively searches a whole tree for subtrees, for which a predicate holds. The search is performed top down. When a tree is found, this becomes an element of the result list. The tree found is not further examined for any subtress, for which the predicate also could hold. See multi for this kind of search.

example: deep isHtmlTable selects all top level table elements in a document (with an appropriate definition for isHtmlTable) but no tables occuring within a table cell.

deepest :: Tree t => a (t b) (t b) -> a (t b) (t b)

recursively searches a whole tree for subrees, for which a predicate holds. The search is performed bottom up.

example: deepest isHtmlTable selects all innermost table elements in a document but no table elements containing tables. See deep and multi for other search strategies.

multi :: Tree t => a (t b) c -> a (t b) c

recursively searches a whole tree for subtrees, for which a predicate holds. The search is performed top down. All nodes of the tree are searched, even within the subtrees of trees for which the predicate holds.

example: multy isHtmlTable selects all table elements, even nested ones.

processBottomUp :: Tree t => a (t b) (t b) -> a (t b) (t b)

recursively transforms a whole tree by applying an arrow to all subtrees, this is done bottom up depth first, leaves first, root as last tree

example: processBottomUp (getChildren `when` isHtmlFont) removes all font tags in a HTML document, even nested ones (with an appropriate definition of isHtmlFont)

processTopDown :: Tree t => a (t b) (t b) -> a (t b) (t b)
similar to processBottomUp, but recursively transforms a whole tree by applying an arrow to all subtrees with a top down depth first traversal strategie. In many cases processBottomUp and processTopDown give same results.
processBottomUpWhenNot :: Tree t => a (t b) (t b) -> a (t b) (t b) -> a (t b) (t b)
recursively transforms a whole tree by applying an arrow to all subtrees, but transformation stops when a predicte does not hold for a subtree, leaves are transformed first
processTopDownUntil :: Tree t => a (t b) (t b) -> a (t b) (t b)

recursively transforms a whole tree by applying an arrow to all subtrees, but transformation stops when a tree is successfully transformed. the transformation is done top down

example: processTopDownUntil (isHtmlTable `guards` tranformTable) transforms all top level table elements into something else, but inner tables remain unchanged

insertChildrenAt :: Tree t => Int -> a (t b) (t b) -> a (t b) (t b)

computes a list of trees by applying an arrow to the input and inserts this list in front of index i in the list of children

example: insertChildrenAt 0 (deep isCmt) selects all subtrees for which isCmt holds and copies theses in front of the existing children

insertChildrenAfter :: Tree t => a (t b) (t b) -> a (t b) (t b) -> a (t b) (t b)
similar to insertChildrenAt, but the insertion position is searched with a predicate
insertTreeTemplate :: Tree t => a (t b) (t b) -> [IfThen (a (t b) c) (a (t b) (t b))] -> a (t b) (t b)

an arrow for inserting a whole subtree with some holes in it (a template) into a document. The holes can be filled with contents from the input.

Example

 insertTreeTemplateTest	:: ArrowXml a => a b XmlTree
 insertTreeTemplateTest
     = doc
       >>>
       insertTemplate template pattern
     where
     doc								-- the input data
 	= constA "<x><y>The Title</y><z>The content</z></x>"
 	  >>> xread
     template								-- the output template with 2 holes: xxx and yyy
 	= constA "<html><head><title>xxx</title></head><body><h1>yyy</h1></body></html>"
 	  >>> xread
     pattern
 	= [ hasText (== "xxx")						-- fill the xxx hole with the input contents from element "x/y"
 	    :-> ( getChildren >>> hasName "y" >>> deep isText )
 
 	  , hasText (== "yyy")						-- fill the yyy hole with the input contents from element "x/z"
 	    :-> ( getChildren >>> hasName "z" >>> getChildren )
 	  ]

computes the XML tree for the following document

 "<html><head><title>The Title</title></head><body><h1>The content</h1></body></html>"
show/hide Instances
class Tree t
The interface for trees
show/hide Instances
Produced by Haddock version 2.1.0