Can't press enter in haskell interactive mode

[alokedesai]

When I press C-c C-l in a haskell buffer, a haskell REPL opens successfully, but I can't press enter to evaluate a haskell expression. Any ideas what this could be? haskell-mode is the only package I have installed and I've also tried reinstalling haskell-mode and even emacs to no avail.

Here's my .emacs file in case you need it

(add-to-list 'load-path "~/.emacs.d/el-get/el-get")

(unless (require 'el-get nil 'noerror)
  (with-current-buffer
      (url-retrieve-synchronously
       "https://raw.githubusercontent.com/dimitri/el-get/master/el-get-install.el")
    (goto-char (point-max))
    (eval-print-last-sexp)))

(add-to-list 'el-get-recipe-path "~/.emacs.d/el-get-user/recipes")
(el-get 'sync)

(add-to-list 'load-path "~/structured-haskell-mode/elisp")
(require 'shm)

(add-hook 'haskell-mode-hook 'structured-haskell-mode)


(require 'haskell-interactive-mode)
(require 'haskell-process)
(add-hook 'haskell-mode-hook 'interactive-haskell-mode)

(custom-set-variables
 '(haskell-process-suggest-remove-import-lines t)
 '(haskell-process-auto-import-loaded-modules t)
   '(haskell-process-log t))

[gracjan]

Can you try to set to nil each of the variables in turn:

'(haskell-process-suggest-remove-import-lines t)
'(haskell-process-auto-import-loaded-modules t)
'(haskell-process-log t)

so that only one of those is set to t and then report what happened?

[alokedesai]

I've tried every possible permutation of setting t to nil in these three lines and none of it worked

[gracjan]

Is there anybody else out there that has similar problem?

[alokedesai]

I've seen this stackoverflow post and another forum post somewhere that I can't remember that both describe similar problems but no fix has been described.

[gracjan]

33 upvotes and you are the first one to report the issue. Thanks for doing that. 33 people will be happy when we fix this one!

[yamafaktory]

Hi there,
I am also experiencing the same weird issue trying to play with the Haskell REPL, i.e. not being able to press enter.
I am using stack on Archlinux, Emacs 24.5.1 and here is part of my settings:

(add-hook 'haskell-mode-hook 'interactive-haskell-mode)
(setq haskell-process-path-ghci "stack")
(custom-set-variables
 '(haskell-process-suggest-remove-import-lines t)
 '(haskell-process-auto-import-loaded-modules t)
 '(haskell-process-log t))
(define-key haskell-mode-map (kbd "C-c h") 'haskell-interactive-switch)

Please note that I tried @gracjan solution without any success.

Any workaround?

[PierreR]

Are you using evil ? Could you check that this is not the same issue as this one;
syl20bnr/spacemacs#3271

If so, workarounds are described there. One of them is to use a to enter the insert mode instead of i.

For the record, I am using the haskell repl with spacemacs on Arch linux and it all works nicely (once you are aware of the problem and workarounds)

[yamafaktory]

Thanks for the guidance! Unfortunately, I am not an evil user.

[yamafaktory]

Well, I found out what the issue was.

Using M-x haskell-process-restart gave me a hint: first stack was launch with the unwanted "-ferror-spans" argument and thus I needed to provide a "ghci" argument instead:

(setq haskell-process-path-ghci "stack")
(setq haskell-process-args-ghci '("ghci"))

Maybe @alokedesai you can give it a try (i.e. checking if ghci is correctly launched).

[d12frosted]

@yamafaktory what is the value of haskell-process-type?

[yamafaktory]

@d12frosted since then I refactored my settings, i.e. only using (setq haskell-process-type 'stack-ghci) which perfectly works.

[d12frosted]

@yamafaktory
Yeah, that's what I wanted to suggest you, cause now (from my experience) haskell-mode plays nice with stack. Also, even if you leave haskell-process-type as auto, it should still work for projects that have stack.yaml file in the project root.

[d12frosted]

@alokedesai are you sure that there is space between λ> and what you type? I know it's silly, but it's very common problem.

[yamafaktory]

@d12frosted thanks for the guidance which should benefit other users! Maybe a stack entry or stack related instructions in the corresponding sections should be added in the wiki.

[d12frosted]

@yamafaktory you are welcome 😄

About the wiki, it already says that there is stack-ghci process type. But it lacks some description on process types. Plus it misleads about the default value of process type. So yeah, updated it. Thanks for the call ! 😄