On 19/07/2011, at 11:09 AM, Patrick Browne wrote:
> data Emperor = Emperor
> data Robin = Robin
>
> class Bird a where
> fly :: a -> a -> a
> walk :: a -> a -> a
>
> instance Bird Robin where
> fly x y = y
> walk x y = x
>
> instance Bird Emperor where
> -- No fly method
> walk x y = y
Note that "no 'fly' method is visibly presented" is
not at all the same thing as "no 'fly' method EXISTS".
From the report:
"The default class method for v sub i is used if
no binding for it is given in a particular
instance declaration (see Section 4.3.2)."
so the absence of a method in 'instance Bird Emperor'
doesn't mean that it doesn't _have_ one, just that it
inherits the default class method.
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