Dependent types do not support extension methods

[jackfoxy]

The DependentType type does not support extension methods. In lieu of this limitation, is it better to add all the desirable overloads to TryParse and Parse? Otherwise users will have to devise their own functions.

If extension methods were possible users could perform all sorts of customizations to dependent types.

[robkuz]

This should be possible with this PR:"[ WIP, F# 4.2 ] Extension members visible to trait constraints #3582" which is Release Candidate for 4.2. Let's hope it makes it into it