case expression inference

src/Rlp/HindleyMilner.hs

@@ -15,6 +15,7 @@ import Control.Monad.Accum
 import Control.Monad.Reader
 import Control.Monad
 import Control.Monad.Extra
+import Control.Monad.Free
 import Control.Arrow            ((>>>))
 import Control.Monad.Writer.Strict
 
@@ -40,7 +41,7 @@ import Debug.Trace
 import Data.Functor             hiding (unzip)
 import Data.Functor.Extend
 import Data.Functor.Foldable    hiding (fold)
-import Data.Fix                 hiding (cata, para, cataM)
+import Data.Fix                 hiding (cata, para, cataM, ana)
 import Control.Comonad.Cofree
 import Control.Comonad
 
@@ -136,11 +137,41 @@ gather (InR (LetEF Rec (withoutPatterns -> bs) (te,je))) = do
     elimRecBind (x,(tx,_)) j = elim x tx j
     elimBind (x,(tx,_)) j = elimGenerally x tx j
 
-gather (InR (CaseEF (te,je) [Alter (ConP' n []) (ta,ja)])) = do
-    tc <- freshTv
-    let j = equal te tc <> je <> assume n tc <> ja
+gather (InR (CaseEF (te,je) as)) = do
+    as' <- gatherAlter te `traverse` as
+    t <- freshTv
+    let eqs = allEqual (t : (as' ^.. each . _1))
+        j = je <> foldOf (each . _2) as' <> eqs
+    pure (t,j)
+
+-- gather (InR (CaseEF (te,je) [Alter (ConP' n bs) (ta,ja)])) = do
+--     -- let tc' be the type of the saturated type constructor
+--     tc' <- freshTv
+--     bs <- for bs (\b -> (b ^. singular _VarP,) <$> freshTv)
+--     let tbs = bs ^.. each . _2
+--         tc = foldr (:->) tc' tbs
+--         j = equal te tc' <> je <> assume n tc <> forBinds elim bs ja
+--     pure (ta,j)
+
+gatherAlter :: (Unique :> es)
+            => Type'
+            -> Alter PsName (Type', Judgement)
+            -> Eff es (Type', Judgement)
+gatherAlter te (Alter (ConP' n bs) (ta,ja)) = do
+    -- let tc' be the type of the saturated type constructor
+    tc' <- freshTv
+    bs' <- for bs (\b -> (b ^. singular _VarP,) <$> freshTv)
+    let tbs = bs' ^.. each . _2
+        tc = foldr (:->) tc' tbs
+        j = equal te tc' <> assume n tc <> forBinds elim bs' ja
     pure (ta,j)
 
+allEqual :: [Type'] -> Judgement
+allEqual = fold . ana @[_] \case
+    [] -> Nil
+    [a] -> Nil
+    (a:b:xs) -> Cons (equal a b) (b:xs)
+
 forBinds :: (PsName -> Type' -> Judgement -> Judgement)
          -> [(PsName, Type')] -> Judgement -> Judgement
 forBinds f bs j = foldr (uncurry f) j bs