[[!comment format=mdwn
 username="joey"
 subject="""comment 5"""
 date="2016-03-08T21:56:26Z"
 content="""
I got it to throw a nice type error when intersection of two OS lists
yields an empty list:

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

I think the next step would be actually adding the OSList to Property
and making combining properties combine their OS lists at the type level.
"""]]
