module Language.PureScript.TypeChecker.Subsumption (
subsumes
) where
import Data.List (sortBy)
import Data.Ord (comparing)
#if __GLASGOW_HASKELL__ < 710
import Control.Applicative
#endif
import Control.Monad.Error.Class (MonadError(..))
import Control.Monad.State.Class (MonadState(..))
import Language.PureScript.Crash
import Language.PureScript.AST
import Language.PureScript.Environment
import Language.PureScript.Errors
import Language.PureScript.TypeChecker.Monad
import Language.PureScript.TypeChecker.Skolems
import Language.PureScript.TypeChecker.Unify
import Language.PureScript.Types
subsumes :: (Functor m, Applicative m, MonadError MultipleErrors m, MonadState CheckState m) => Maybe Expr -> Type -> Type -> m (Maybe Expr)
subsumes val ty1 ty2 = rethrow (addHint (ErrorInSubsumption ty1 ty2)) $ subsumes' val ty1 ty2
subsumes' :: (Functor m, Applicative m, MonadError MultipleErrors m, MonadState CheckState m) =>
Maybe Expr ->
Type ->
Type ->
m (Maybe Expr)
subsumes' val (ForAll ident ty1 _) ty2 = do
replaced <- replaceVarWithUnknown ident ty1
subsumes val replaced ty2
subsumes' val ty1 (ForAll ident ty2 sco) =
case sco of
Just sco' -> do
sko <- newSkolemConstant
let sk = skolemize ident sko sco' Nothing ty2
subsumes val ty1 sk
Nothing -> internalError "subsumes: unspecified skolem scope"
subsumes' val (TypeApp (TypeApp f1 arg1) ret1) (TypeApp (TypeApp f2 arg2) ret2) | f1 == tyFunction && f2 == tyFunction = do
_ <- subsumes Nothing arg2 arg1
_ <- subsumes Nothing ret1 ret2
return val
subsumes' val (KindedType ty1 _) ty2 =
subsumes val ty1 ty2
subsumes' val ty1 (KindedType ty2 _) =
subsumes val ty1 ty2
subsumes' (Just val) (ConstrainedType constraints ty1) ty2 = do
dicts <- getTypeClassDictionaries
subsumes' (Just $ foldl App val (map (flip TypeClassDictionary dicts) constraints)) ty1 ty2
subsumes' val (TypeApp f1 r1) (TypeApp f2 r2) | f1 == tyObject && f2 == tyObject = do
let
(ts1, r1') = rowToList r1
(ts2, r2') = rowToList r2
ts1' = sortBy (comparing fst) ts1
ts2' = sortBy (comparing fst) ts2
go ts1' ts2' r1' r2'
return val
where
go [] ts2 r1' r2' = unifyTypes r1' (rowFromList (ts2, r2'))
go ts1 [] r1' r2' = unifyTypes r2' (rowFromList (ts1, r1'))
go ((p1, ty1) : ts1) ((p2, ty2) : ts2) r1' r2'
| p1 == p2 = do _ <- subsumes Nothing ty1 ty2
go ts1 ts2 r1' r2'
| p1 < p2 = do rest <- freshType
case r2' of
REmpty -> throwError . errorMessage $ AdditionalProperty p1
_ -> unifyTypes r2' (RCons p1 ty1 rest)
go ts1 ((p2, ty2) : ts2) r1' rest
| otherwise = do rest <- freshType
case r1' of
REmpty -> throwError . errorMessage $ PropertyIsMissing p2
_ -> unifyTypes r1' (RCons p2 ty2 rest)
go ((p1, ty1) : ts1) ts2 rest r2'
subsumes' val ty1 ty2@(TypeApp obj _) | obj == tyObject = subsumes val ty2 ty1
subsumes' val ty1 ty2 = do
unifyTypes ty1 ty2
return val