From 74a5cf52a7fcf09552b259d4962c1eebe948ad21 Mon Sep 17 00:00:00 2001
From: Neil Brown <neil@twistedsquare.com>
Date: Sun, 23 Mar 2008 12:15:00 +0000
Subject: [PATCH] Stopped constants being assigned to in the type-checker for
 Rain

---
 frontends/RainTypes.hs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/frontends/RainTypes.hs b/frontends/RainTypes.hs
index d590801..afc43b6 100644
--- a/frontends/RainTypes.hs
+++ b/frontends/RainTypes.hs
@@ -307,6 +307,9 @@ checkAssignmentTypes = applyDepthM checkAssignment
     checkAssignment ass@(A.Assign m [v] (A.ExpressionList m' [e]))
       = do trhs <- typeOfExpression e
            tlhs <- typeOfVariable v
+           am <- abbrevModeOfVariable v
+           when (am == A.ValAbbrev) $
+             diePC m $ formatCode "Cannot assign to a constant variable: %" v
            if (tlhs == trhs)
              then return ass
              else do rhs' <- coerceType " in assignment" tlhs trhs e