functions.el

(defun get-comint-candidates ()
  (let ((start (car comint-input-ring))
        (end (car (cdr comint-input-ring)))
        (completed (append (nthcdr 2 comint-input-ring) nil))
        ))
  (butlast (nthcdr start baz) (- (length baz) end))
  )

(defun comint-completion-source ()
  (interactive)
  (helm :sources '((name . "helm comint-mode")
                   (candidates . get-comint-candidates)
                   (action . (lambda (cand) (insert cand)))
                   )
        :input (thing-at-point 'word)
        )
  )

(add-hook 'comint-mode-hook (lambda () (setq completion-at-point-functions 'comint-completion-source)))
(setq tab-always-indent 'complete)