val master = fn (EApp ((EVar "externalMaster", _), e), _) => Option.map ExternalMaster (ip e)
| (EApp ((EVar "internalMaster", _), e), _) => Option.map InternalMaster (Env.string e)
val master = fn (EApp ((EVar "externalMaster", _), e), _) => Option.map ExternalMaster (ip e)
| (EApp ((EVar "internalMaster", _), e), _) => Option.map InternalMaster (Env.string e)