Since i cannot comment on answers, i have to do this as an answer itself, which is simply an addition to Matt Elands solution.

In case you get the errors: "Undefined CLR namespace. The 'clr-namespace' URI refers to a namespace 'System' that could not be found." or "The name "Double" does not exist in the namespace "clr-namespace:System": You need to add the assembly mscorlib to the xmlns :

xlmns:sys="clr-namespace:System;assembly=mscorlib"