From 32f8a3e8a98bf898810ad4bad6e753d7ceaa99d8 Mon Sep 17 00:00:00 2001
From: sebastianselander <sebastian.selander@gmail.com>
Date: Fri, 24 Mar 2023 11:27:19 +0100
Subject: [PATCH] duplicate signatures disallowed

---
 src/TypeChecker/TypeChecker.hs | 5 +++--
 test_program                   | 1 +
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/TypeChecker/TypeChecker.hs b/src/TypeChecker/TypeChecker.hs
index 712c1cd..9f1879b 100644
--- a/src/TypeChecker/TypeChecker.hs
+++ b/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
diff --git a/test_program b/test_program
index ded8250..eb31907 100644
--- a/test_program
+++ b/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 {