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POWhat is a higher kinded type in Scala?
 

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    <p>You can find the following on the web:</p> <ol> <li><p><strong>Higher kinded type == type constructor?</strong></p> <blockquote> <pre class="lang-scala prettyprint-override"><code>class AClass[T]{...} // For example, class List[T] </code></pre> </blockquote> <p>Some say this is a higher kinded type, because it abstracts over types which would be compliant with the definition.</p> <blockquote> <p><em>Higher kinded types</em> are types which take other types and construct a new type</p> </blockquote> <p>These though are also known as <em>type constructor</em>. (For example, in <a href="http://www.artima.com/pins1ed/type-parameterization.html#19.3">Programming in Scala</a>).</p></li> <li><p><strong>Higher kinded type == type constructor which takes type constructor as a type parameter?</strong></p> <p>In the paper <a href="http://adriaanm.github.com/files/higher.pdf">Generics of a Higher Kind</a>, you can read</p> <blockquote> <p>... types that abstract over types that abstract over types ('higher-kinded types') ..."</p> </blockquote> <p>which suggests that</p> <blockquote> <pre class="lang-scala prettyprint-override"><code>class XClass[M[T]]{...} // or trait YTrait[N[_]]{...} // e.g. trait Functor[F[_]] </code></pre> </blockquote> <p>is a higher kinded type.</p></li> </ol> <p>So with this in mind, it is difficult to distinguish between <em>type constructor</em>, <em>higher kinded type</em> and <em>type constructor which takes type constructors as type parameter</em>, therefore the question above.</p>
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    1. COAdded Landei's Functor as example.
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