Calling XPath-function from XSLT Element handler

Hello!

I've registered external module (test), external element (test:foo)
and external XPath-function (test:bar). I need to call test:bar from
test:foo C++ handler so that test:bar will "see" all current XSLT
entities (stylesheet variables, etc).

Please look at this short code example. I've created XML that contains
one empty root node and XSL that contains one variable ($var) and one
test:foo element. When I perform XSL transformation, I need to
evaluate XPath-expression from test:foo handler, that contains
test:bar($var) call:

http://www.everfall.com/paste/id.php?wlyu7lb528hy

I didn't find how can I evaluate XPath-expression with registred
external XPath function, and how can I make current XSLT-environment
visible for this XPath-expression. The point isn't in making visible
one single variable either one single function. The point is in making
all external functions and XSLT-environment visible from this
XPath-expression. Any suggestions?

Thanks!

Denis.