What you posted is the format for data declarations, not newtypes. Newtypes are required to have exactly one constructor: 

newtype
 [context =>] simpletype = newconstr [deriving]


Adam

On Fri, Aug 12, 2016 at 4:43 PM, James Brown <james.brown5374@gmail.com> wrote:
In the Haskell report 2010, a data declaration has the format of:

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? 


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