Improve error message (Trac #4799)

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

diff --git a/compiler/typecheck/TcBinds.lhs b/compiler/typecheck/TcBinds.lhs
index f4f7e47..9f11ade 100644 (file)
--- a/compiler/typecheck/TcBinds.lhs
+++ b/compiler/typecheck/TcBinds.lhs
@@ -583,8 +583,8 @@ tcImpSpec p = pprPanic "tcImpSpec" (ppr p)
 impSpecErr :: Name -> SDoc
 impSpecErr name
   = hang (ptext (sLit "You cannot SPECIALISE") <+> quotes (ppr name))
-       2 (ptext (sLit "because its definition has no INLINE/INLINABLE pragma"))
-
+       2 (vcat [ ptext (sLit "because its definition has no INLINE/INLINABLE pragma")
+               , ptext (sLit "(or you compiled its definining module without -O)")])
 --------------
 -- If typechecking the binds fails, then return with each
 -- signature-less binder given type (forall a.a), to minimise 
@@ -1076,6 +1076,7 @@ instance Outputable GeneralisationPlan where
 decideGeneralisationPlan 
    :: DynFlags -> TopLevelFlag -> [Name] -> [LHsBind Name] -> TcSigFun -> GeneralisationPlan
 decideGeneralisationPlan dflags top_lvl _bndrs binds sig_fn
+  | bang_pat_binds                         = NoGen
   | mono_pat_binds                         = NoGen
   | Just sig <- one_funbind_with_sig binds = if null (sig_tvs sig) && null (sig_theta sig)
                                              then NoGen              -- Optimise common case
@@ -1085,7 +1086,12 @@ decideGeneralisationPlan dflags top_lvl _bndrs binds sig_fn
   | otherwise                              = InferGen mono_restriction
 
   where
-    mono_pat_binds = xopt Opt_MonoPatBinds dflags 
+    bang_pat_binds = any (isBangHsBind . unLoc) binds
+       -- Bang patterns must not be polymorphic,
+       -- because we are going to force them
+       -- See Trac #4498
+
+    mono_pat_binds = xopt Opt_MonoPatBinds dflags
                   && any (is_pat_bind . unLoc) binds
 
     mono_restriction = xopt Opt_MonomorphismRestriction dflags 
@@ -1129,24 +1135,30 @@ checkStrictBinds top_lvl rec_group binds poly_ids
         ; checkTc (isNonRec rec_group)
                   (strictBindErr "Recursive" unlifted binds)
         ; checkTc (isSingleton binds)
-                  (strictBindErr "Multiple" unlifted binds) 
+                  (strictBindErr "Multiple" unlifted binds)
         -- This should be a checkTc, not a warnTc, but as of GHC 6.11
         -- the versions of alex and happy available have non-conforming
         -- templates, so the GHC build fails if it's an error:
         ; warnUnlifted <- doptM Opt_WarnLazyUnliftedBindings
-        ; warnTc (warnUnlifted && not bang_pat)
+        ; warnTc (warnUnlifted && not bang_pat && lifted_pat)
+                 -- No outer bang, but it's a compound pattern
+                 -- E.g   (I# x#) = blah
+                 -- Warn about this, but not about
+                 --      x# = 4# +# 1#
+                 --      (# a, b #) = ...
                  (unliftedMustBeBang binds) }
   | otherwise
   = return ()
   where
-    unlifted = any is_unlifted poly_ids
-    bang_pat = any (isBangHsBind . unLoc) binds
+    unlifted    = any is_unlifted poly_ids
+    bang_pat    = any (isBangHsBind . unLoc) binds
+    lifted_pat  = any (isLiftedPatBind . unLoc) binds
     is_unlifted id = case tcSplitForAllTys (idType id) of
                        (_, rho) -> isUnLiftedType rho
 
 unliftedMustBeBang :: [LHsBind Name] -> SDoc
 unliftedMustBeBang binds
-  = hang (text "Bindings containing unlifted types should use an outermost bang pattern:")
+  = hang (text "Pattern bindings containing unlifted types should use an outermost bang pattern:")
        2 (pprBindList binds)
 
 strictBindErr :: String -> Bool -> [LHsBind Name] -> SDoc