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copied!<p>You can not have anything like </p> <pre><code>data Sub = SubA | SubB data Super = Sub | SuperB </code></pre> <p>Suppose the above syntax is allowed, then the problem is given the value constructor <code>SubA</code> you can not tell whether its type is <code>Sub</code> or <code>Super</code>. That's why you need to wrap your type in a constructor.</p> <p>For your second example, the way you are doing should be the default way of doing but you can do a hack to make it easier although I don't recommend doing this as using show is much slower. You can try some other hack similar to this. </p> <pre><code>import Data.List data Super = SubA | SubB | SuperB deriving Show isSub :: Super -> Bool isSub m = isPrefixOf "Sub" (show m) </code></pre> <p>If you really want to have something like above it is better to define function like you did. Using TH might save you sometime.</p> <p>Your third case is what I would really recommend doing. You need to have a wrapper constructor like <code>SuperA</code> because of the reasons I told above. That's why you can't have exactly type1 is of type2 plus x,y,z. The closest thing you can have is to wrap elements in a constructor or using a typeclass. </p> <pre><code>data Sub = SubA | SubB data Sup = SuperA | SuperB class Super a where isSub :: a -> Bool isSub _ = True instance Super Sup where isSub _ = False instance Super Sub data SupSup = SuperSuperA | SuperSuperB class SuperSuper a where isSuper :: a -> Bool isSuper _ = True instance SuperSuper SupSup where isSuper _ = False instance SuperSuper Sup instance SuperSuper Sub </code></pre> <p>You can think here <code>Super</code> (which is a typeclass and not a type) contains <code>Sub</code> and someting extra (<code>Sup</code>).</p>

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