Order is relevant when matching signature contexts of a mutually recursive group

The Following code

f :: (Show a, Eq a) => a -> String
f x = show x `const` g x

g :: (Eq a,Show a) => a -> Bool
g x = x==x `const` f x

gives this error:

    Couldn't match expected type `Eq a' against inferred type `Show a1'
    When matching the contexts of the signatures for
      f :: forall a. (Show a, Eq a) => a -> String
      g :: forall a. (Eq a, Show a) => a -> Bool
    The signature contexts in a mutually recursive group should all be identical
    When generalising the type(s) for f, g
Failed, modules loaded: none.

but it compiles fine if i swap Show and Eq in the context of either f or g. The order of typeclass constraints usually doesn't matter so it's very surprising that it does here.

Trac metadata

Trac field	Value
Version	6.8.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	sanzhiyan@gmail.com
Operating system	Unknown
Architecture	Unknown

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