- Install the Hasklig font to 
~/.fonts. - Modify your emacs configuration 
.emacs.d/init.el. 
Example configuration:
(set-face-attribute 'default nil
                    :family "Hasklig"
                    :height 200
                    :weight 'normal
                    :width 'normal)
(use-package hasklig-mode
  :hook (haskell-mode))