Here's what the GHCi session should look like.
$ ghci GHCi, version 8.0.0.20160204: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/callen/.ghci Prelude> let myList = [1..5 :: Integer] Prelude> let myList' = myList ++ undefined Prelude> :t myList' myList' :: HasCallStack => [Integer]
If your readers are using :t they must already know about simple types like Integer, [], and, ->, so the new things are HasCallStack and =>. This is how I would explain them. => is just like -> except the compiler fills in the argument by itself. HasCallStack tells the compiler that the expression needs a call-stack because it might crash. So HasCallStack => [Integer] is a [Integer] that might crash and produce a stack-trace. I think the call-stacks are much less scary and confusing than type-classes in general, which you kind of have to deal with as soon as you talk about arithmetic. Eric