From 51bfcc0e6baad4032a6892a3e7d44a9e52b0961e Mon Sep 17 00:00:00 2001
From: Simon Peyton Jones <simonpj@microsoft.com>
Date: Tue, 17 Jan 2012 08:35:38 +0000
Subject: [PATCH] Allow default superclass methods for multi-parameter type
classes
They were prohibited by mistake, a historical hangover
---
compiler/typecheck/TcTyClsDecls.lhs | 16 ++--------------
1 file changed, 2 insertions(+), 14 deletions(-)
diff --git a/compiler/typecheck/TcTyClsDecls.lhs b/compiler/typecheck/TcTyClsDecls.lhs
index f91ccdf43d6d..ba1b011e82f5 100644
--- a/compiler/typecheck/TcTyClsDecls.lhs
+++ b/compiler/typecheck/TcTyClsDecls.lhs
@@ -1365,17 +1365,10 @@ checkValidClass cls
-- Check the associated type defaults are well-formed and instantiated
-- See Note [Checking consistent instantiation]
- ; mapM_ check_at_defs at_stuff
-
- -- Check that if the class has generic methods, then the
- -- class has only one parameter. We can't do generic
- -- multi-parameter type classes!
- ; checkTc (unary || no_generics) (genericMultiParamErr cls)
- }
+ ; mapM_ check_at_defs at_stuff }
where
(tyvars, fundeps, theta, _, at_stuff, op_stuff) = classExtraBigSig cls
- unary = isSingleton (snd (splitKiTyVars tyvars)) -- IA0_NOTE: only count type arguments
- no_generics = null [() | (_, (GenDefMeth _)) <- op_stuff]
+ unary = isSingleton (snd (splitKiTyVars tyvars)) -- IA0_NOTE: only count type arguments
check_op constrained_class_methods (sel_id, dm)
= addErrCtxt (classOpCtxt sel_id tau) $ do
@@ -1700,11 +1693,6 @@ noClassTyVarErr clas op
ptext (sLit "mentions none of the type variables of the class") <+>
ppr clas <+> hsep (map ppr (classTyVars clas))]
-genericMultiParamErr :: Class -> SDoc
-genericMultiParamErr clas
- = ptext (sLit "The multi-parameter class") <+> quotes (ppr clas) <+>
- ptext (sLit "cannot have generic methods")
-
recSynErr :: [LTyClDecl Name] -> TcRn ()
recSynErr syn_decls
= setSrcSpan (getLoc (head sorted_decls)) $
--
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