duplicate signatures disallowed

src/TypeChecker/TypeChecker.hs

@@ -85,8 +85,9 @@ checkPrg (Program bs) = do
     preRun :: [Def] -> Infer ()
     preRun [] = return ()
     preRun (x : xs) = case x of
-        -- TODO: Check for no overlapping signature definitions
-        DSig (Sig n t) -> insertSig (coerce n) (Just $ toNew t) >> preRun xs
+        DSig (Sig n t) -> do
+            gets (M.member (coerce n) . sigs) >>= flip when (throwError $ "Duplicate signatures for function '" ++ printTree n ++ "'")
+            insertSig (coerce n) (Just $ toNew t) >> preRun xs
         DBind (Bind n _ _) -> do
             s <- gets sigs
             case M.lookup (coerce n) s of

test_program

@@ -21,6 +21,7 @@ data Bool () where {
 --     Cons x xs => x
 -- };
 
+firstIsOne : List (Int) -> Bool () ;
 firstIsOne : List (Int) -> Bool () ;
 firstIsOne xs = case xs of {
     Cons x xs => case x of {