diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/Propellor/Types/OS/Typelevel.hs | 15 |
1 files changed, 11 insertions, 4 deletions
diff --git a/src/Propellor/Types/OS/Typelevel.hs b/src/Propellor/Types/OS/Typelevel.hs index 82f3a426..879259df 100644 --- a/src/Propellor/Types/OS/Typelevel.hs +++ b/src/Propellor/Types/OS/Typelevel.hs @@ -43,9 +43,8 @@ freeBSD = typeOS OSFreeBSD typeOS :: SupportedOS -> OSList os typeOS o = OSList [o] --- FIXME, should type check --- foo :: OSList '[OSDebian, OSFreeBSD] --- foo = (debian `combineSupportedOS` freeBSD ) `intersectSupportedOS` unixlike +foo :: OSList '[OSDebian, OSFreeBSD] +foo = (debian `combineSupportedOS` freeBSD ) `intersectSupportedOS` unixlike -- | Combines two lists of supported OS's, yielding a list with the -- contents of both. @@ -63,12 +62,20 @@ type instance ConcatOSList (a ': rest) list2 = a ': ConcatOSList rest list2 -- | The intersection between two lists of supported OS's. intersectSupportedOS - :: (r ~ IntersectOSList l1 l2) + :: (r ~ IntersectOSList l1 l2, CannotCombineOS l1 l2 r ~ CanCombineOS) => OSList l1 -> OSList l2 -> OSList r intersectSupportedOS (OSList l1) (OSList l2) = OSList (filter (`elem` l2) l1) +-- | Detect intersection of two lists that don't have any common OS. +-- +-- The name of this was chosen to make type errors a more understandable. +type family CannotCombineOS (list1 :: [a]) (list2 :: [a]) (listr :: [a]) :: CheckIntersection +type instance CannotCombineOS l1 l2 '[] = 'CannotCombineOS +type instance CannotCombineOS l1 l2 (a ': rest) = 'CanCombineOS +data CheckIntersection = CannotCombineOS | CanCombineOS + -- | Type level intersection for OSList type family IntersectOSList (list1 :: [a]) (list2 :: [a]) :: [a] type instance IntersectOSList '[] list2 = '[] |