Re: [Haskell-cafe] How to define Show [MyType] ?

If you really, really wanted to define Show [ShipInfo], then putting

{-# LANGUAGE FlexibleInstances, OverlappingInstances #-}

at the beginning of your file would work. At the cost of using overlapping instances, of course.

And at the cost of causing code like this:

f :: Show a => [a] -> String f xs = show xs

to fail to compile (see "Incoherent Instances"). Implement "showList"; it's the Right Answer for this case.