<div dir="ltr"><span style="font-family:Arial,Helvetica,sans-serif;font-size:13px">In the Haskell report 2010, a data declaration has the format of:</span><p style="margin:1em 0px;padding:0px;border:0px;font-family:Arial,Helvetica,sans-serif;font-size:13px;clear:both"><a href="https://lh3.googleusercontent.com/-G-z92n-50B0/V63XKCCrJDI/AAAAAAAAAGA/w-Zdi9DaR18hX67n-OeQNkDB1iUR0IP7gCLcB/s1600/Screen%2BShot%2B2016-08-12%2Bat%2B10.03.00%2BAM.png" target="_blank" rel="nofollow" style="margin:0px 1em;padding:0px;border:0px;text-decoration:none;color:rgb(102,17,204)"><img src="https://lh3.googleusercontent.com/-G-z92n-50B0/V63XKCCrJDI/AAAAAAAAAGA/w-Zdi9DaR18hX67n-OeQNkDB1iUR0IP7gCLcB/s320/Screen%2BShot%2B2016-08-12%2Bat%2B10.03.00%2BAM.png" border="0" width="320" height="25" style="margin: 0px; padding: 0px; border: 0px;"></a></p><p style="margin:1em 0px;padding:0px;border:0px;font-family:Arial,Helvetica,sans-serif;font-size:13px;clear:both">For a new type, there could be zero or more data constructors. What's the use case for a new type that has zero data constructor? </p></div>