module THInstanceReification
(
reifyProperInstances,
isProperInstance,
typesSatisfyDecConstraints,
)
where
import THInstanceReification.Prelude.Basic
import THInstanceReification.Prelude.TH
import qualified Data.Map as Map
reifyProperInstances :: Name -> [Type] -> Q [InstanceDec]
reifyProperInstances n tl =
reifyInstances n tl >>= filterM (typesSatisfyDecConstraints tl)
isProperInstance :: Name -> [Type] -> Q Bool
isProperInstance n tl =
not . null <$> reifyProperInstances n tl
typesSatisfyDecConstraints :: [Type] -> InstanceDec -> Q Bool
typesSatisfyDecConstraints tl = \case
InstanceD context instanceType _ -> do
let ([ConT n], htl) = splitAt 1 $ reverse $ unapplyType instanceType
expandedTypes <- mapM expandSyns tl
expendedInstanceTypes <- mapM expandSyns htl
maybe
(fail $ "Unmatching amounts of types: " <> show expandedTypes <> ", " <>
show expendedInstanceTypes)
(analyze context)
(pair expandedTypes expendedInstanceTypes)
d -> fail $ "Not an instance dec: " <> show d
where
analyze :: Cxt -> [(Type, Type)] -> Q Bool
analyze context typeAssocs = and <$> mapM analyzePredicate context
where
actualTypeByVarName :: Name -> Type
actualTypeByVarName = \n ->
Map.lookup n m ?:
($bug $ "Unexpected key: " <> show n <> ", in a map: " <> show m)
where
m = Map.fromList $ concat $ map accRecords $ typeAssocs
where
accRecords = \case
(AppT al ar, AppT hl hr) -> accRecords (al, hl) ++ accRecords (ar, hr)
(a, VarT n) -> [(n, a)]
(a, h) | a /= h -> $bug $ "Unmatching types: " <> show a <> ", " <> show h
_ -> []
analyzePredicate :: Pred -> Q Bool
analyzePredicate = \case
EqualP _ _ -> return True
ClassP n tl -> do
let tl' = map (replaceTypeVars actualTypeByVarName) tl
isProperInstance n tl'
unapplyType :: Type -> [Type]
unapplyType = \case
AppT l r -> r : unapplyType l
t -> [t]
replaceTypeVars :: (Name -> Type) -> Type -> Type
replaceTypeVars f = \case
AppT l r -> AppT (replaceTypeVars f l) (replaceTypeVars f r)
VarT n -> f n
t -> t