I've added a test case illustrating the fact that FilePath cannot easily be used in config types: Since it is an alias to [Char], the yaml parser expects a list of chars (which appear to have the same syntax as strings), with dashes and everything.

I have no idea how to make this work, and whether it should be considered a bug / missing feature in the first place. The work-around is simple: use text or bytestring or a newtype, and call conversion functions by hand after extracting the value from the config structure to get to the char list.