haskell repl in emacs

Question

Hi i am starting with haskell and trying to set up my emacs for its development.

I have haskell-mod and ghc-mod latest in emacs 24.3.1. GHC is 7.6.3

i have created a haskell file first.hs and when i do C-c C-l It asks :

start a new project named haskell ? y or n

my directory name is haskell. I press y

Set the cabal directory

I have tried with both ~/.cabal and my current directory named haskell

Set the current directory

Just pressed enter as it has haskell directory

It shows error messages :

haskell-process-start: cl-ecase failed: cabal-rep, (ghci quote cabal-repl quote cabal-ghci quote cabal-dev quote)

How can i get the repl ?

I read that i may need to downgrad the ghc version to make it work. Is that good solution ?

Solution :

I had multiple custom-set-variables in init.el and it led to the problem.

Answer 1

UPDATE 2017

now that we have Intero I would suggest you try Intero/Stack - it works rather well.

With it my config is slimmed even more down:

;; ----------------------------------------------------------------------
;; HASKELL
(require 'haskell-mode)
(require 'intero)
(add-hook 'haskell-mode-hook 'intero-mode)
(require 'flycheck)
(setq flycheck-check-syntax-automatically '(save new-line))
(flycheck-add-next-checker 'intero '(warning . haskell-hlint))

Concerning the REPL you basically just load the file and then C-c C-l into the repl (you can always switch between the two windows with C-c C-z and you can clear out the repl-buffer with C-c C-k (when inside).

The only drawback is that Intero is usually installed locally in your project, so the first startup into a new project will take a while for Intero to download/compile/boot-up - but it's no big deal and you gain much.

---

UPDATE

Now that stack is out and running great I would recommend setting the haskell-process-type to auto and maybe installing ghc-mod using stack.

here is the current setup I am using:

(require 'haskell-mode)
(add-hook 'haskell-mode-hook 'turn-on-haskell-doc-mode)
(add-hook 'haskell-mode-hook 'turn-on-haskell-indentation)
(add-hook 'haskell-mode-hook 'linum-mode)
(add-to-list 'exec-path "~/.local/bin")
(eval-after-load 'haskell-mode '(progn
  (define-key haskell-mode-map (kbd "C-c C-l") 'haskell-process-load-file)
  (define-key haskell-mode-map (kbd "C-c C-n C-t") 'haskell-process-do-type)
  (define-key haskell-mode-map (kbd "C-c C-n C-i") 'haskell-process-do-info)
  (define-key haskell-mode-map "\C-ch" 'haskell-hoogle)))
(eval-after-load 'haskell-cabal '(progn
  (define-key haskell-cabal-mode-map (kbd "C-c C-k") 'haskell-interactive-ode-clear)
  (define-key haskell-cabal-mode-map (kbd "C-c C-c") 'haskell-process-cabal-build)
  (define-key haskell-cabal-mode-map (kbd "C-c c") 'haskell-process-cabal)))

(require 'company-ghci)
(push 'company-ghci company-backends)
(add-hook 'haskell-mode-hook 'company-mode)
(add-hook 'haskell-interactive-mode-hook 'company-mode)

As you can see I basically got rid of all ghc-mod related stuff (stack works as is with the current haskell-mode) and replaced the company backend (although this one is really slow and I hope to find something better)

variables

Theses you usually set within Emacs/Configuration of Haskell-Mode

(custom-set-variables
 ;; there is of course more in here - these are the Haskell related:
 '(haskell-font-lock-symbols (quote unicode))
 '(haskell-hoogle-command nil)
 '(haskell-mode-hook
   (quote
    (linum-mode turn-on-haskell-indentation turn-on-haskell-doc-mode)) t)
 '(haskell-process-auto-import-loaded-modules t)
 '(haskell-process-load-or-reload-prompt t)
 '(haskell-process-log t)
 '(haskell-process-suggest-language-pragmas nil)
 '(haskell-process-suggest-no-warn-orphans t)
 '(haskell-process-type (quote auto))
 '(haskell-process-use-presentation-mode t)
 '(haskell-tags-on-save t)
 '(inferior-haskell-wait-and-jump t)
 '(safe-local-variable-values
   (quote
    ((haskell-process-use-ghci . t)
     (haskell-indent-spaces . 4))))
 (uniquify)))

These are the packages I added:

• haskell-mode
• company (not Haskell-related as is but a dependency)
• company-cabal
• company-ghci
• ghci-completion
• shakespeare-mode (for Yesod)
• company-quickhelp (for nice display of :i)

---

First

if it asks for your cabal directory - it wants to know where your myProject.cabal file is - if you don't have one just take the folder where your file is (the default - I think the default/find never failed me till now).

in case you need some sample-.emacs-setup

Here are parts from my .emacs file that works for me:

(autoload 'ghc-init "ghc" nil t)
(autoload 'ghc-debug "ghc" nil t)
(add-hook 'haskell-mode-hook (lambda () (ghc-init)))
(add-hook 'haskell-mode-hook 'turn-on-haskell-indentation)

(eval-after-load 'haskell-mode '(progn
  (define-key haskell-mode-map (kbd "C-c C-l") 'haskell-process-load-or-reload)
  (define-key haskell-mode-map (kbd "C-`") 'haskell-interactive-bring)
  (define-key haskell-mode-map (kbd "C-c C-n C-t") 'haskell-process-do-type)
  (define-key haskell-mode-map (kbd "C-c C-n C-i") 'haskell-process-do-info)
  (define-key haskell-mode-map (kbd "C-c C-n C-c") 'haskell-process-cabal-build)
  (define-key haskell-mode-map (kbd "C-c C-n c") 'haskell-process-cabal)))
(eval-after-load 'haskell-cabal '(progn
  (define-key haskell-cabal-mode-map (kbd "C-`") 'haskell-interactive-bring)
  (define-key haskell-cabal-mode-map (kbd "C-c C-k") 'haskell-interactive-ode-clear)
  (define-key haskell-cabal-mode-map (kbd "C-c C-c") 'haskell-process-cabal-build)
  (define-key haskell-cabal-mode-map (kbd "C-c c") 'haskell-process-cabal)))

(custom-set-variables
 '(haskell-interactive-mode-hide-multi-line-errors nil)
 '(haskell-process-log t)
 '(haskell-process-type (quote cabal-repl)))

Please note the part with (quote cabal-repl) - this should work with cabal sandboxes. Also this will add more logging information to a buffer named haskell-process-log where you might find more about your problem.

I use this with ghc-mod version 5.1.0.2 compiled by GHC 7.8.3 and GHC 7.8.3 obviously.

Of course you have to make sure that your .cabal folder and the place where ghc-mod is in your path (I think you can configure this somewhere in the emacs settings too - but it's much easier this way).

remarks

• you have to install the package ghc in emacs not ghc-mod.
• I had problems with different version of ghc-mod and the emacs package before - so make sure that you get the latest with cabal-install and then reinstall the emacs-package (was only problems with parsing of the ghc-output on my part though)

further information

If this does not help you please feel free to

• add a comment
• have a look at the happy haskell programming page
• have a look at the ghc wiki on emacs

sample run on my machine

I edited a sample file like this:

Then I hit C-c C-l and press y:

And accept the folder (this is where the file is located) and any other questions with Ret - now you should see the *haskell* buffer with a friendly message/lambda:

Finally I can check that the file got loaded: