Custom functions not visible/available in let expressions

[mikaelforslund]

Looks like custom functions kept in the functionTable are lost when a new scope is created in TreeInterpreter.ts.

I can create a PR for a fix if nobody is working on that at the moment?

[springcomp]

Hi @mikaelforslund thanks for your feedback.
If you have a test that exhibits this issue then a PR would be greatly appreciated.