Effective Haskell

Looking Up Type Information

As you’re writing Haskell and working with types, there are two ghci commands that will be immensely helpful to you. The :type command, which we often abbreviate :t, will give you the type of an arbitrary Haskell expression, and the :info command, which is often abbreviated :i, will give you a bit more information, but not for an arbitrary expression. :info will only work for functions that you’ve loaded in from a module or source file. Let’s look at a few examples of using :type to get the type information from some expressions. You won’t understand many of the types here yet, but as you work your way through the chapter, you’ll get a chance to use all of the features individually, and by the end, you’ll be able ...