Repository : ssh://g...@git.haskell.org/ghc
On branch : master
Link :
http://ghc.haskell.org/trac/ghc/changeset/4407614cb19a65ddb2f9ede4778a0b47396f8ec9/ghc
>---------------------------------------------------------------
commit 4407614cb19a65ddb2f9ede4778a0b47396f8ec9
Author: unknown <simo...@msrc-4971295.europe.corp.microsoft.com>
Date: Thu Sep 26 19:10:04 2013 +0100
Look inside tuple predicates when checking instance declaration contexts
This fixes Trac #8359
>---------------------------------------------------------------
4407614cb19a65ddb2f9ede4778a0b47396f8ec9
compiler/typecheck/TcValidity.lhs | 26 ++++++++++++++++++--------
1 file changed, 18 insertions(+), 8 deletions(-)
diff --git a/compiler/typecheck/TcValidity.lhs
b/compiler/typecheck/TcValidity.lhs
index 7d02866..963d67f 100644
--- a/compiler/typecheck/TcValidity.lhs
+++ b/compiler/typecheck/TcValidity.lhs
@@ -915,18 +915,28 @@ The underlying idea is that
checkInstTermination :: [TcType] -> ThetaType -> TcM ()
-- See Note [Paterson conditions]
checkInstTermination tys theta
- = mapM_ check theta
+ = check_preds theta
where
fvs = fvTypes tys
size = sizeTypes tys
+
+ check_preds :: [PredType] -> TcM ()
+ check_preds preds = mapM_ check preds
+
+ check :: PredType -> TcM ()
check pred
- | not (null bad_tvs)
- = addErrTc (predUndecErr pred (nomoreMsg bad_tvs) $$ parens
undecidableMsg)
- | sizePred pred >= size
- = addErrTc (predUndecErr pred smallerMsg $$ parens undecidableMsg)
- | otherwise
- = return ()
- where
+ = case classifyPredType pred of
+ TuplePred preds -> check_preds preds -- Look inside tuple
predicates; Trac #8359
+ EqPred {} -> return () -- You can't get from equalities
+ -- to class predicates, so this
is safe
+ _other -- ClassPred, IrredPred
+ | not (null bad_tvs)
+ -> addErrTc (predUndecErr pred (nomoreMsg bad_tvs) $$ parens
undecidableMsg)
+ | sizePred pred >= size
+ -> addErrTc (predUndecErr pred smallerMsg $$ parens undecidableMsg)
+ | otherwise
+ -> return ()
+ where
bad_tvs = filterOut isKindVar (fvType pred \\ fvs)
-- Rightly or wrongly, we only check for
-- excessive occurrences of *type* variables.
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