Fix an old but subtle bug in the Simplifier

[ghc-hetmet.git] / compiler / simplCore / SimplEnv.lhs

diff --git a/compiler/simplCore/SimplEnv.lhs b/compiler/simplCore/SimplEnv.lhs
index 1b05737..d0240fb 100644 (file)
--- a/compiler/simplCore/SimplEnv.lhs
+++ b/compiler/simplCore/SimplEnv.lhs
@@ -456,14 +456,16 @@ floatBinds (Floats bs _) = fromOL bs
 
 \begin{code}
 substId :: SimplEnv -> Id -> SimplSR
+-- Returns DoneEx only on a non-Var expression
 substId (SimplEnv { seInScope = in_scope, seIdSubst = ids }) v 
   | not (isLocalId v) 
   = DoneId v
   | otherwise  -- A local Id
   = case lookupVarEnv ids v of
-       Just (DoneId v) -> DoneId (refine in_scope v)
-       Just res        -> res
-       Nothing         -> DoneId (refine in_scope v)
+       Nothing               -> DoneId (refine in_scope v)
+       Just (DoneId v)       -> DoneId (refine in_scope v)
+       Just (DoneEx (Var v)) -> DoneId (refine in_scope v)
+       Just res              -> res    -- DoneEx non-var, or ContEx
   where
 
        -- Get the most up-to-date thing from the in-scope set