GHC cannot solve functional dependency

GHC fails to compile following program:

{-# LANGUAGE MultiParamTypeClasses  #-}
{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE FlexibleInstances      #-}
{-# LANGUAGE FlexibleContexts       #-}
{-# LANGUAGE UndecidableInstances   #-}
{-# LANGUAGE TypeOperators          #-}
{-# LANGUAGE DataKinds              #-}
{-# LANGUAGE KindSignatures         #-}


-- | All unordered pairs of elements of lists. If list is set result
-- will be set as well.
class TyPairs (xs :: [*]) (ys :: [*]) | xs -> ys

instance                                 TyPairs '[]      '[]
instance TyAddPairs x (x ': xs) xs ys => TyPairs (x ': xs) ys

-- Add all pairs for /x/ and /xs/ and that build all pairs for the
-- remaining part of the list.
class TyAddPairs x (xs :: [*]) (rest :: [*]) (pairs :: [*]) | x xs rest -> pairs

instance TyPairs    ys rs      => TyAddPairs x '[] ys rs
instance TyAddPairs x xs ys rs => TyAddPairs x (a ': xs) ys ((x,a) ': rs)



data K = K
data B = B

type List  = '[K,B]
type Pairs = '[(K,K), (K,B), (B,B)]

data Row (vars :: [*]) = Row

failure :: TyPairs List r => Row r
failure = Row :: Row Pairs

fine :: TyPairs List Pairs => ()
fine = ()

with following error message:

OKA/Statistics/fail.hs:36:11:
    Could not deduce (r
                      ~ (':) * (K, K) ((':) * (K, B) ((':) * (B, B) ('[] *))))
    from the context (TyPairs List r)
      bound by the type signature for failure :: TyPairs List r => Row r
      at OKA/Statistics/fail.hs:35:12-34
      `r' is a rigid type variable bound by
          the type signature for failure :: TyPairs List r => Row r
          at OKA/Statistics/fail.hs:35:12
    Expected type: Row r
      Actual type: Row Pairs
    In the expression: Row :: Row Pairs
    In an equation for `failure': failure = Row :: Row Pairs
Failed, modules loaded: none.

r is determined by functional dependency so it looks like bug to me.

Trac metadata

Trac field	Value
Version	7.6.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	alexey.skladnoy@gmail.com
Operating system
Architecture