[project @ 2000-07-18 14:50:32 by simonpj]

Arrange that type signatures that have no "parent" signatures
work right.  For example

	   module A
	      f :: Int -> Int

The panic in RnEnv.lookupBndrRn becomes an error message.  Also
RnBinds.rnTopMonoBinds and rnMonoBinds were wrongly ignoring all
signatures altogether if there were no bindings!

ghc/compiler/rename/RnBinds.lhs

@@ -165,9 +165,6 @@ rnTopBinds (MonoBind bind sigs _) 	  = rnTopMonoBinds bind sigs
   -- The parser doesn't produce other forms
 
 
-rnTopMonoBinds EmptyMonoBinds sigs 
-  = returnRn (EmptyBinds, emptyFVs)
-
 rnTopMonoBinds mbinds sigs
  =  mapRn lookupBndrRn binder_rdr_names		`thenRn` \ binder_names ->
     let
@@ -218,8 +215,6 @@ rnMonoBinds :: RdrNameMonoBinds
 	    -> (RenamedHsBinds -> RnMS (result, FreeVars))
 	    -> RnMS (result, FreeVars)
 
-rnMonoBinds EmptyMonoBinds sigs thing_inside = thing_inside EmptyBinds
-
 rnMonoBinds mbinds sigs	thing_inside -- Non-empty monobinds
   =	-- Extract all the binders in this group,
 	-- and extend current scope, inventing new names for the new binders
@@ -284,7 +279,7 @@ rn_mono_binds siglist mbinds
     let 
         edges	    = mkEdges (mbinds_info `zip` [(0::Int)..])
 	scc_result  = stronglyConnComp edges
-	final_binds = foldr1 ThenBinds (map reconstructCycle scc_result)
+	final_binds = foldr (ThenBinds . reconstructCycle) EmptyBinds scc_result
 
 	 -- Deal with bound and free-var calculation
 	rhs_fvs = plusFVs [fvs | (_,fvs,_,_) <- mbinds_info]

ghc/compiler/rename/RnEnv.lhs

@@ -452,7 +452,14 @@ lookupBndrRn rdr_name
 		case lookupRdrEnv global_env (qualifyRdrName mod rdr_name) of
 		  Just (name:rest) -> ASSERT( null rest )
 				      returnRn name 
-		  Nothing	   -> pprPanic "lookupBndrRn" (ppr mod <+> ppr rdr_name)
+		  Nothing	   -> 	-- Almost always this case is a compiler bug.
+					-- But consider a type signature that doesn't have 
+					-- a corresponding binder: 
+					--	module M where { f :: Int->Int }
+					-- We use lookupSigOccRn, which uses lookupBndrRn (for good reasons)
+					-- and we don't want to panic.  So we report an out-of-scope error
+					failWithRn (mkUnboundName rdr_name)
+						   (unknownNameErr rdr_name)
     }
 
 -- lookupOccRn looks up an occurrence of a RdrName