XPath selection for simple XPath expressions with list arrows instead of navigatable trees.

It is recomended, that this module is imported qualified, e.g like Text.XML.HXT.Arrow.XPathSimple as XS.

The arrows defined in this module have the same functionality as the functions in Text.XML.HXT.Arrow.XPath.

The computation modell in XPath is a navigatable tree, that means a tree wicht can be traveresed in arbitrary directions, not only from the root to the leafs. Sometimes this modell leads to inefficent XPath processing for simple queries, which only need a top down tree traversal.

When evaluating an XPath expression with these functions, first an attempt is made to map the XPath expression to a pure arrow. If this is possible due to the siplicity of the XPath expressions, the result is computed directly, else the query is processed by the corresponding function in Text.XML.HXT.Arrow.XPath.

The simple evaluation is possible, when in the XPath expression only the top down axis (self, child, descendant, descendant or self are used, when no builtin functions concerning the position of a node are used, and no comparison of nodes e.g. in node set union is required.

The xpath interpreter for simple xpath expressions.

In case of a too complicated or illegal xpath expression an error node is returned, else the list of selected XML trees