I'm getting the following error:

sheet.rb:35:in `values': stack level too deep (SystemStackError)
        from sheet.rb:35:in `values'
        from sheet.rb:53:in `to_s'
        from sheet.rb:52:in `to_s'
        from sheet.rb:52:in `map'
        from sheet.rb:52:in `to_s'
        from sheet.rb:52:in `to_s'
        from sheet.rb:52:in `map'
        from sheet.rb:52:in `to_s'
        from sheet.rb:52:in `to_s'
        from sheet.rb:52:in `map'
        from sheet.rb:52:in `to_s'
        from sheet.rb:92

The output above is given _in full_. Is Ruby truncating the call stack 
in this output? If  so, how I can I see a larger snapshot of the stack, 
so I can trace down where the infinite recursion is really happening? If 
not, why am I getting this error?

Thanks,
Ken