From 0a07bb2f351aa3315fde0768db723650f23c31b6 Mon Sep 17 00:00:00 2001
From: Michael Andreen <harv@ruin.nu>
Date: Mon, 27 Feb 2006 13:47:05 +0000
Subject: [PATCH] typechecker finds redeclaration of a variable

---
 Typecheck.hs              | 4 +++-
 examples/typeerror-redecl | 2 ++
 2 files changed, 5 insertions(+), 1 deletion(-)
 create mode 100644 examples/typeerror-redecl

diff --git a/Typecheck.hs b/Typecheck.hs
index 6e845ba..ec40b1f 100644
--- a/Typecheck.hs
+++ b/Typecheck.hs
@@ -70,7 +70,9 @@ typeCheckStm (SDecl t i e) = do
 	t2 <- typeCheckExp e
 	if t == t2 || t2 == NoType then do
 		m <- get
-		put (insert i t m)
+		case insertLookupWithKey (\k a1 a2 -> a1) i t m of 
+			(Nothing,m') -> put m'
+			_ -> fail $ "Duplicate variable declaration: "++show i
 		return NoType
 		else fail $ "Illegal to assign an expression of type "++show t2++" to variable "++show i++" of type "++show t
 typeCheckStm (SPrint e) = do
diff --git a/examples/typeerror-redecl b/examples/typeerror-redecl
new file mode 100644
index 0000000..c96734e
--- /dev/null
+++ b/examples/typeerror-redecl
@@ -0,0 +1,2 @@
+int a = 0;
+int a = 5;
-- 
2.39.2