IHaskell
A Haskell kernel for the Jupyter project
... that will help. You can write your own extensions using the IPython javascript API, for instance. Use h to learn more about the modal interface IHaskell/IPython provides. IHaskell adds a few features on top of the IPython frontends, such as automatic character concealing (typing -> yields an arrow) and input cell folding (via the left and right arrow keys, or the buttons). If input cell folding isn't showing up, you can explicitly enable it via the "Cell Toolbar" (select 'Hiding').