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POHaskell Refactoring Advice
 

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    <p>I am looking for some refactoring / Best practice advice on the following code. I would like to try to avoid the extensions while maintaining separate modules for different "versions" that are mutually exclusive. My current solution is to use a class and use existential quantification to create a common type for each of the <code>CountrySets</code>.</p> <p>This is an easy thing for me to accomplish if I was using OOP, but I can't seam to think "functional" yet.</p> <p>Thanks for your time.</p> <p><strong>Province.hs</strong></p> <pre><code>{-# LANGUAGE ExistentialQuantification, RankNTypes #-} module Province where class Country a where --some stuff that is not important data Power = forall a. (Show a, Eq a, Country a) =&gt; Power a | Netural | Water data Unit = Unit { power :: forall a. (Show a, Eq a, Country a) =&gt; a, piece :: Piece data Piece = Tank | Plane data Province = Province { power :: Power, provName :: String } deriving (Eq) instance Show Power where show (Power b) = "Power " ++ show b show (Netural) = "Netural" show (Water) = "Water" instance Eq Power where (==) a b = Prelude.show a == Prelude.show b </code></pre> <p><strong>Version1.hs</strong></p> <pre><code>import Province data CountrySet1 = Country11 | Country12 deriving (Eq, Show) instance Country CountrySet1 where provs = one1:one2:[] one1 = Province (Power Country11) "Place11" one2 = Province (Power Country12) "Place12" </code></pre> <p><strong>Version2.hs</strong></p> <pre><code>import Province data CountrySet2 = Country21 | Country22 deriving (Eq, Show) instance Country CountrySet2 where provs = two1:two2:[] two1 = Province (Power Country11) "Place21" two2 = Province (Power Country12) "Place22" </code></pre>
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    1. COI think this is a good candidate for the [Code Review](http://codereview.stackexchange.com/) site. However, I don't use it myself so I'm not 100% certain it fits their criteria.
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    2. COI'll post it there and see what I get.
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