title: Type constructor for integers in Haskell
body: <p>I'm just beginning to learn Haskell and I'm stuck at the following problem:</p>
  
  <p>I want to create a type of the calendar weeks, i.e. the numbers from 1 to 52. 
  That's why I tried this one:</p>
  
  <pre><code>data CalendarWeek = 1 | 2 | ... | 52 deriving (Eq, Order, Show)
  </code></pre>
  
  <p>So then it could be used right here:</p>
  
  <pre><code>data Offer = Offer CalendarWeek Day Offer String deriving (Eq, Order, Show)
  </code></pre>
  
  <p>However, GHC just prints out the following error:</p>
  
  <pre><code>parse error on input `1'
  </code></pre>
  
  <p>What am I doing wrong? Is there another way to build this type? </p>
  
  <p>Thanks a lot for your answers!</p>