I've spent rather too many hours today trying to get this code to fail to build with a type error.

intersectSupportedOS debian freeBSD

Here's the final type error in all its glory!

    Couldn't match type ‘'CannotCombineOS’ with ‘'CanCombineOS’
    Expected type: 'CanCombineOS
      Actual type: CannotCombineOS '['OSDebian] '['OSFreeBSD] '[]
    In the expression: intersectSupportedOS debian freeBSD