:11:1: No instance for (Show a1) arising from a use of `print' Cannot resolve unknown runtime type `a1' Use :print or :force to determine these types Relevant bindings include it :: a1 (bound at :11:1) Note: there are several potential instances: instance Show a => Show (List1 a) -- Defined at ../Test.hs:11:12 instance Show MyInt -- Defined at ../Test.hs:14:16 instance Show a => Show (MkT a) -- Defined at ../Test.hs:17:13 ...plus 31 others In a stmt of an interactive GHCi command: print it