Configure Flycheck for Haskell:

• Add source directories from your cabal project to the search path
• Add build files and auto-generated files from Cabal to the search path
• Use package databases from the current Cabal sandbox
• Set the language from Cabal
• Enable language extensions from Cabal

As usual, from MELPA or MELPA Stable.

In your Cask file:

(source gnu)
(source melpa)

(depends-on "flycheck-haskell")

In your init.el:

(eval-after-load 'flycheck
  '(add-hook 'flycheck-mode-hook #'flycheck-haskell-setup))

Just use Flycheck as usual in your Cabal projects.

To explicitly configure Haskell syntax checking for the current buffer, type M-x flycheck-haskell-configure. You should run this command after major changes to the Cabal file.

• M-x customize-group RET flycheck-haskell

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.

See COPYING for details.