Dante is a fork of Intero mode. It steals many good ideas from Intero, but it aims for light weightedness (see below for a detailed comparison).

(*) REPLoid explanation:

You can evaluate code by writing it in a comment of the form {-> [code to evaluate] -} and run dante-eval-block.

Example:

example :: [String]
example = ["This is an example", "of", "interactive", "evaluation"]

{-> intercalate " " example

-}

In the above file, if you invoke dante-eval-block on the line containing “intercalate”, you’ll get:

{-> intercalate " " example

"This is an example of interactive evaluation"
-}

Turn on Dante in your haskell-mode-hook. I recommend:

(use-package dante
  :ensure t
  :commands 'dante-mode
  :init
  (add-hook 'haskell-mode-hook 'dante-mode)
  (add-hook 'haskell-mode-hook 'flycheck-mode))

You may want to be sure not to enable (interactive-haskell-mode) so that Dante keybindings are not hidden.

You can activate the hlint checker in addition to the dante checker as follows:

(add-hook 'dante-mode-hook
   '(lambda () (flycheck-add-next-checker 'haskell-dante
                '(warning . haskell-hlint)))

Use M-x customize-group dante

To the best of my knowledge, here is how Dante compares with Intero:

• Dante has no dependency on “Stack”
• Dante’s Emacs code is about half as long as that of Intero.
• Dante does not depend on custom Haskell code, contrary to intero. Thus, it will if (and only if) GHCi works for your project. (Including via “Stack”).
• Dante supports xref-find-definitions and xref-find-references.
• With Dante, Flychecking is optional (yet recommended), whereas Intero demands that you flycheck your code.
• Dante has has a different approach to Haskell evaluation
• Dante offers no support for Hoogle nor eldoc.