Module XCuery

with :: Data a => [a] -> [a]   

The operation with evaluates to all lists containing the elements in the argument in the same order. For instance,

> with [1,2]
1:2:_a
1:_a:2:_b
1:_a:_b:2:_c
...

This operation can be used in a pattern to match XML structures having at least the given elements as children, as in

getNamePhone
  (xml "entry"
       (with [xml "name"  [xtxt name],
              xml "phone" [xtxt phone]])) = name ++ ": " ++ phone

xml' :: String -> [XmlExp] -> XmlExp   

The operation xml' can be used to match an XML structure with a given tag and children independent of the attributes. For instance,

getName (xml’ "entry" (with [xml’ "name" [xtxt n]])) = n

matches an XML element with tag entry and some child element with tag name, independent of the possible attributes attached to these elements.

anyorder :: [a] -> [a]   

The operation anyorder returns all permutations of the input list. It can be used in a pattern to match XML structures with the given elements in arbitrary order, as in

getNamePhone
  (xml "entry"
    (with (anyorder [xml "name"  [xtxt name],
                     xml "phone" [xtxt phone]]))) = name ++ ": " ++ phone

Further infos:

• solution complete, i.e., able to compute all solutions

deepXml :: String -> [XmlExp] -> XmlExp   

The operation deepXml evaluates to any XML structure containing an XML structure with the given tag and children at an abritrarily deep position. For instance,

getNamePhone
  (deepXml "entry"
           (with [xml "name"  [xtxt name],
                  xml "phone" [xtxt phone]])) = name ++ ": " ++ phone

allows to query an XML structure having a structure with tag entry and children structures with tags name and phone.

deepXml' :: String -> [XmlExp] -> XmlExp   

This operation is similar to deepXml but matches the XML structures independent of their attributes.

deepXElem :: String -> [(String,String)] -> [XmlExp] -> XmlExp   

This operation is similar to deepXml but allows to provide a list of attributes to the matched XML structures. For instance,

getMaleFirstNames
  (deepXElem "first" (with [("sex","male")]) [xtxt f]) = f

matches an XML structure containing an XML structure with tag first and some attribute sex with value male.

noTagOf :: String -> [XmlExp] -> Bool   

The predicate noTagOf returns True if the given tag is not a tag of all argument XML structures.

withOthers :: Data a => [a] -> [a] -> [a]   

The operation withOthers is similar to with but has a second argument that contains the child nodes that are present but not part of the first argument. One can use this operation to denote the unmatched part of an XML structure in order to put conditions on it. For instance, if one wants to get the name and phone number of an entry that has no email address, one can use the following definition:

getNamePhoneWithoutEmail
  (deepXml "entry"
     (withOthers [xml "name" [xtxt name], xml "phone" [xtxt phone]]
                 others))
  | "email" `noTagOf` others
  = name ++ ": " ++ phone

optXml :: String -> [XmlExp] -> [XmlExp] -> XmlExp   

The operation optXml can be used in transformations of XML elements to insert a structure with a given tag depending on the presence of this tag in a list of XML strucutres. For this purpose, optXml t xs ys evaluates to xml t xs if there is no element with tag t in ys, otherwise the first element of ys with tag t is returned.

The following definition shows a usage of optXml:

transNickPhone
  (deepXml "entry"
           (withOthers [xml "name"  [xtxt n],
                        xml "first" [xtxt f],
                        xml "phone" phone]
                       others)) =
  xml "nickphone" [optXml "nickname" [xtxt (f++n)] others,
                   xml "phone" phone]