Fixed type-checking on ambigious record fields, so that now the cgtests are happy again

common/Types.hs

@@ -215,19 +215,19 @@ subscriptType sub t = diePC (findMeta sub) $ formatCode "Unsubscriptable type: %
 
 -- | The inverse of 'subscriptType': given a type that we know is the result of
 -- a subscript, return what the type being subscripted is.
-unsubscriptType :: (CSMR m, Die m) => A.Subscript -> A.Type -> m A.Type
+unsubscriptType :: A.Subscript -> A.Type -> Maybe A.Type
 unsubscriptType _ A.Infer
-    = return $ A.Infer
+    = Just $ A.Infer
 unsubscriptType (A.SubscriptFromFor _ _ _ _) t
-    = return $ removeFixedDimension t
+    = Just $ removeFixedDimension t
 unsubscriptType (A.SubscriptFrom _ _ _) t
-    = return $ removeFixedDimension t
+    = Just $ removeFixedDimension t
 unsubscriptType (A.SubscriptFor _ _ _) t
-    = return $ removeFixedDimension t
+    = Just $ removeFixedDimension t
 unsubscriptType (A.SubscriptField m _) t
-    = dieP m $ "unsubscript of record type (but we can't tell which one)"
+    = Nothing
 unsubscriptType (A.Subscript _ _ sub) t
-    = return $ addDimensions [A.UnknownDimension] t
+    = Just $ addDimensions [A.UnknownDimension] t
 
 -- | Just remove the first dimension from an array type -- like doing
 -- subscriptType with constant 0 as a subscript, but without the checking.

frontends/OccamTypes.hs

@@ -686,10 +686,7 @@ inferTypes = occamOnlyPass "Infer types"
             A.IntrinsicFunctionCall _ _ _ -> noTypeContext $ descend outer
             A.SubscriptedExpr m s e ->
                do ctx <- getTypeContext
-                  ctx' <- case ctx of
-                            Just t -> unsubscriptType s t >>* Just
-                            Nothing -> return Nothing
-                  e' <- inTypeContext ctx' $ recurse e
+                  e' <- inTypeContext (ctx >>= unsubscriptType s) $ recurse e
                   t <- astTypeOf e'
                   s' <- recurse s >>= fixSubscript t
                   return $ A.SubscriptedExpr m s' e'