Overloaded functions in XPath 1.0?

An application I’m working on needs to be able to evaluate XPath 1.0 expressions.  In addition to the standard XPath core functions, we need to introduce an application-specific function that retrieves a value from a data structure internal to the app.  Lets call it ‘getvalue()’.  This value could be a String, Boolean or Number.  Would it be a violation of XPath practices for this ‘getvalue()’ function to be an overloaded function, returning String, Number and Boolean (e.g. three functions: string getvalue(), boolean getvalue(), number getvalue())?  My alternative would be to use unique function names such as getstring(), getboolean() and getnumber()...