Deriving a type and its dependencies
I've been playing with newtype wrappers for my indexes to avoid 开发者_JAVA技巧bugs, and I have some code like this:
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
newtype PersonIdx = PersonIdx Int
deriving (Enum, Eq, Integral, Num, Ord, Real, Show)
To derive Integral
, one must derive all its dependencies as well (hence the above list of type-classes).
Is there a way to make it derive all the dependencies of Integral
along with it? I would imagine something like:
newtype PersonIdx = PersonIdx Int
deriving (Integral(..))
No, there is no shortcut. You'll have to derive from all dependent typeclasses explicitly, but can easily find these by typing :i Integral
in ghci.
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