How can I declare an empty tuple?

Question

I can declare empty list as [], but, how can I declare empty tuple?

I have tried:

for ( , ) 
ghci>(1,0 ) : [(,)] 

but it gives me an error!

Answer 1

A tuple is a type that is always the same length and always has the same types. So (Int, Int) is a different type from (Int, Int, Int) and a different type from (Int, String).

With this in mind, you could have an empty tuple. However, this would just be a type with a single value. This type is written as () and pronounced unit. The only value of this type is also ().