GHC allow-overlapping-instances

[H X]

Hi,

Does anyone have ever used this option? 
I see no difference when I present this program to ghc
with -fallow-overlapping-instances on/off:

module Test where


data T = T
data F = F

data OR a b = OR a b
data AND a b = AND a b

class C a b | a -> b

instance C (OR T r) T
instance C (OR r T) T

instance C (AND F r) F
instance C (AND r F) F

-Kenny

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