Neil Mitchell wrote:
In what way is the document() function not pure?
See [http://www.w3schools.com/xsl/func_document.asp]. In particular their example:
i.e. this function needs to load the file celsius.xml. Note that instead of celsius.xml there could be an arbitrary complex expression here, that builds up a filename.
That is, the static context is defined to include a mapping from URIs to document nodes, and document() returns those document nodes that it's argument nodes map to.
I think I understand what you are saying, but might have missed slightly. While you can consider it as a mapping from URI to document node, there are an infinite number of URI's, and therefore an infinite amount of context. A more practical implementation would be to retrieve the document nodes as they are requested, and then cache them - but this means having IO to do the initial retrieve.
A function you could have in Haskell that would make some of these things pure is getFileReader :: IO (FilePath -> String) which would return a (semantically pure) function that maps file names to file contents. -- Lennart