[project @ 2000-03-23 17:45:17 by simonpj]

[ghc-hetmet.git] / ghc / compiler / typecheck / TcSimplify.lhs

diff --git a/ghc/compiler/typecheck/TcSimplify.lhs b/ghc/compiler/typecheck/TcSimplify.lhs
index f3a3c07..b05225f 100644 (file)
--- a/ghc/compiler/typecheck/TcSimplify.lhs
+++ b/ghc/compiler/typecheck/TcSimplify.lhs
@@ -255,7 +255,7 @@ tcSimplify str local_tvs wanted_lie
 
       -- We're infering (not checking) the type, and 
       -- the inst constrains a local type variable
-      | isDict inst  = DontReduce              -- Dicts
+      | isDict inst  = DontReduceUnlessConstant        -- Dicts
       | otherwise    = ReduceMe AddToIrreds    -- Lits and Methods
 \end{code}
 
@@ -405,7 +405,10 @@ data WhatToDo
  = ReduceMe              -- Try to reduce this
        NoInstanceAction  -- What to do if there's no such instance
 
- | DontReduce            -- Return as irreducible
+ | DontReduce                  -- Return as irreducible 
+
+ | DontReduceUnlessConstant    -- Return as irreducible unless it can
+                               -- be reduced to a constant in one step
 
  | Free                          -- Return as free
 
@@ -652,7 +655,11 @@ reduce stack try_me wanted state@(avails, frees, irreds)
 
 
     ;
-    DontReduce ->    -- It's irreducible (or at least should not be reduced)
+
+    DontReduce -> add_to_irreds
+    ;
+
+    DontReduceUnlessConstant ->    -- It's irreducible (or at least should not be reduced)
         -- See if the inst can be reduced to a constant in one step
        lookupInst wanted         `thenNF_Tc` \ lookup_result ->
        case lookup_result of