Hello,

This code runs ok http://lpaste.net/91814 but only thanks to enforcing [()] on line 12.

In GHCI

*Main> :t (List [])

(List []) :: NestedList a

and

*Main> :t flatten (List [])

flatten (List []) :: [a]

That means ghc cannot infer the type.

Is there a way how to # print flatten (List []) ?

Or even more general, print [] without enforcing the type?

Thank you

Lukas