[Haskell-beginners] Newtype to avoid orphans
adrien at haxaire.org
Mon Feb 6 10:31:50 CET 2012
In the library I am writing, I declare a type Vector for Data.Vector
Double. I then create a Num instance for it as it doesn't have one yet.
GHC tells me that this instance is an orphan. After reading several
answers to issues like mine, I want to get rid of these orphans. The
advice I saw mostly is to use the newtype keyword.
Is there a way to do it nicely, instead of copying most of the API of
Now, the only thing I can see is do like in this example:
import Data.Vector as V
newtype VectorD = VectorD (V.Vector Double)
map :: (Double -> Double) -> VectorD -> VectorD
map f (VectorD v) = VectorD $ V.map f v
Is there a better way ?
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