Default implementations in type classes

• Add a /= operation, which defaults to negation

  • class Eq a where (==), (/=) :: a -> a -> Bool x /= y = not (x==y)

• instance (Eq a,Eq b)=> Eq(a,b) where (x1,y1) == (x2,y2) = x1==x2 and y1 == y2 --inherits default /=, -- but could override

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