GHCi REPL-style completions for company-mode

haskell-completion.el

(require 'cl-lib)
(require 'thingatpt)

(defun haskell-process-completions-at-point ()
  "A company-mode-compatible complete-at-point function."
  (-when-let (process (haskell-process))
    (-when-let (symbol (symbol-at-point))
      (destructuring-bind (start . end) (bounds-of-thing-at-point 'symbol)
        (let ((completions (haskell-process-get-repl-completions (haskell-process)
                                                                 (symbol-name symbol))))
          (list start end completions))))))

(add-hook 'haskell-mode-hook
          (lambda ()
            (setq-local completion-at-point-functions
                        '(haskell-process-completions-at-point))))

This is now integrated into haskell-mode, so find it there m'friends...