[Haskell-cafe] Optional "Default" instances of classes in certain subcases (but too broad)

[Juan Casanova]

Correction to my last email:

-- The following would not work because there is no instance Class1  
NT1 NT1 NT2
deriving via (NT2) instance Class1 NT1 NT1 Int

-- But this would work
deriving via (NT2) instance Class1 NT1 NT2 Int


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