haskell-mode-contextual-space called on zero length identifier

[RasmusWL]

I tried turning on debug-on-error in my emacs, and it comes up with the following error when performing a haskell-mode-contextual-space. This bug seems to break the current session, as nothing happens when i call haskell-process-cabal-build.

Debugger entered--Lisp error: (wrong-type-argument stringp nil)
  string-match("^[A-Za-z_]" nil)
  #[(state) "\301�@\302\303�A\"\203��\304\305�A\"\202��\304\306�A\"\"\207" [state haskell-process-send-string string-match "^[A-Za-z_]" format ":info %s" ":info (%s)"] 5]((((name . "futhark") (current-response-cursor . 0) (current-response . "") (command-queue) (inferior-process . #<process futhark>) (is-restarting) (current-command . [cl-struct-haskell-command #0 #[(state) "\301�@\302\303�A\"\203��\304\305�A\"\202��\304\306�A\"\"\207" [state haskell-process-send-string string-match "^[A-Za-z_]" format ":info %s" ":info (%s)"] 5] nil #[(state response) "\301\302�\"\206��\301\303�\"?\205��\304�!\207" [response string-match "^Top level" "^<interactive>" haskell-mode-message-line] 3]]) (suggested-imported) (sent-stdin) (evaluating) (session (name . "futhark") (ignored-files "/home/rasmus/uni/flat/futhark/.ghci" "/home/rasmus/uni/flat/futhark") (interactive-buffer . #<buffer *futhark*>) (current-dir . "/home/rasmus/uni/flat/futhark/") (target . "") (cabal-checksum . "7e75d6e37133be0705f160ed78fc3dd7") (cabal-dir . "/home/rasmus/uni/flat/futhark/") (process (name . "futhark") (current-response-cursor . 0) (current-response . "") (command-queue) (inferior-process . #<process futhark>) (is-restarting) (current-command . [cl-struct-haskell-command #0 #[(state) "\301�@\302\303�A\"\203��\304\305�A\"\202��\304\306�A\"\"\207" [state haskell-process-send-string string-match "^[A-Za-z_]" format ":info %s" ":info (%s)"] 5] nil #[(state response) "\301\302�\"\206��\301\303�\"?\205��\304�!\207" [response string-match "^Top level" "^<interactive>" haskell-mode-message-line] 3]]) (suggested-imported) (sent-stdin) (evaluating) #2)))))
  haskell-command-exec-go([cl-struct-haskell-command (((name . "futhark") (current-response-cursor . 0) (current-response . "") (command-queue) (inferior-process . #<process futhark>) (is-restarting) (current-command . #0) (suggested-imported) (sent-stdin) (evaluating) (session (name . "futhark") (ignored-files "/home/rasmus/uni/flat/futhark/.ghci" "/home/rasmus/uni/flat/futhark") (interactive-buffer . #<buffer *futhark*>) (current-dir . "/home/rasmus/uni/flat/futhark/") (target . "") (cabal-checksum . "7e75d6e37133be0705f160ed78fc3dd7") (cabal-dir . "/home/rasmus/uni/flat/futhark/") (process (name . "futhark") (current-response-cursor . 0) (current-response . "") (command-queue) (inferior-process . #<process futhark>) (is-restarting) (current-command . #0) (suggested-imported) (sent-stdin) (evaluating) #3)))) #[(state) "\301�@\302\303�A\"\203��\304\305�A\"\202��\304\306�A\"\"\207" [state haskell-process-send-string string-match "^[A-Za-z_]" format ":info %s" ":info (%s)"] 5] nil #[(state response) "\301\302�\"\206��\301\303�\"?\205��\304�!\207" [response string-match "^Top level" "^<interactive>" haskell-mode-message-line] 3]])
  haskell-process-trigger-queue(((name . "futhark") (current-response-cursor . 0) (current-response . "") (command-queue) (inferior-process . #<process futhark>) (is-restarting) (current-command . [cl-struct-haskell-command (#0) #[(state) "\301�@\302\303�A\"\203��\304\305�A\"\202��\304\306�A\"\"\207" [state haskell-process-send-string string-match "^[A-Za-z_]" format ":info %s" ":info (%s)"] 5] nil #[(state response) "\301\302�\"\206��\301\303�\"?\205��\304�!\207" [response string-match "^Top level" "^<interactive>" haskell-mode-message-line] 3]]) (suggested-imported) (sent-stdin) (evaluating) (session (name . "futhark") (ignored-files "/home/rasmus/uni/flat/futhark/.ghci" "/home/rasmus/uni/flat/futhark") (interactive-buffer . #<buffer *futhark*>) (current-dir . "/home/rasmus/uni/flat/futhark/") (target . "") (cabal-checksum . "7e75d6e37133be0705f160ed78fc3dd7") (cabal-dir . "/home/rasmus/uni/flat/futhark/") (process (name . "futhark") (current-response-cursor . 0) (current-response . "") (command-queue) (inferior-process . #<process futhark>) (is-restarting) (current-command . [cl-struct-haskell-command (#0) #[(state) "\301�@\302\303�A\"\203��\304\305�A\"\202��\304\306�A\"\"\207" [state haskell-process-send-string string-match "^[A-Za-z_]" format ":info %s" ":info (%s)"] 5] nil #[(state response) "\301\302�\"\206��\301\303�\"?\205��\304�!\207" [response string-match "^Top level" "^<interactive>" haskell-mode-message-line] 3]]) (suggested-imported) (sent-stdin) (evaluating) #1))))
  haskell-process-queue-command(((name . "futhark") (current-response-cursor . 0) (current-response . "") (command-queue) (inferior-process . #<process futhark>) (is-restarting) (current-command . [cl-struct-haskell-command (#0) #[(state) "\301�@\302\303�A\"\203��\304\305�A\"\202��\304\306�A\"\"\207" [state haskell-process-send-string string-match "^[A-Za-z_]" format ":info %s" ":info (%s)"] 5] nil #[(state response) "\301\302�\"\206��\301\303�\"?\205��\304�!\207" [response string-match "^Top level" "^<interactive>" haskell-mode-message-line] 3]]) (suggested-imported) (sent-stdin) (evaluating) (session (name . "futhark") (ignored-files "/home/rasmus/uni/flat/futhark/.ghci" "/home/rasmus/uni/flat/futhark") (interactive-buffer . #<buffer *futhark*>) (current-dir . "/home/rasmus/uni/flat/futhark/") (target . "") (cabal-checksum . "7e75d6e37133be0705f160ed78fc3dd7") (cabal-dir . "/home/rasmus/uni/flat/futhark/") (process (name . "futhark") (current-response-cursor . 0) (current-response . "") (command-queue) (inferior-process . #<process futhark>) (is-restarting) (current-command . [cl-struct-haskell-command (#0) #[(state) "\301�@\302\303�A\"\203��\304\305�A\"\202��\304\306�A\"\"\207" [state haskell-process-send-string string-match "^[A-Za-z_]" format ":info %s" ":info (%s)"] 5] nil #[(state response) "\301\302�\"\206��\301\303�\"?\205��\304�!\207" [response string-match "^Top level" "^<interactive>" haskell-mode-message-line] 3]]) (suggested-imported) (sent-stdin) (evaluating) #1))) [cl-struct-haskell-command (((name . "futhark") (current-response-cursor . 0) (current-response . "") (command-queue) (inferior-process . #<process futhark>) (is-restarting) (current-command . #0) (suggested-imported) (sent-stdin) (evaluating) (session (name . "futhark") (ignored-files "/home/rasmus/uni/flat/futhark/.ghci" "/home/rasmus/uni/flat/futhark") (interactive-buffer . #<buffer *futhark*>) (current-dir . "/home/rasmus/uni/flat/futhark/") (target . "") (cabal-checksum . "7e75d6e37133be0705f160ed78fc3dd7") (cabal-dir . "/home/rasmus/uni/flat/futhark/") (process (name . "futhark") (current-response-cursor . 0) (current-response . "") (command-queue) (inferior-process . #<process futhark>) (is-restarting) (current-command . #0) (suggested-imported) (sent-stdin) (evaluating) #3)))) #[(state) "\301�@\302\303�A\"\203��\304\305�A\"\202��\304\306�A\"\"\207" [state haskell-process-send-string string-match "^[A-Za-z_]" format ":info %s" ":info (%s)"] 5] nil #[(state response) "\301\302�\"\206��\301\303�\"?\205��\304�!\207" [response string-match "^Top level" "^<interactive>" haskell-mode-message-line] 3]])
  haskell-process-do-try-info(nil)
  haskell-mode-contextual-space()
  ad-Orig-call-interactively(haskell-mode-contextual-space nil nil)
  (with-no-warnings (ad-Orig-call-interactively function record-flag keys))
  (setq ad-return-value (with-no-warnings (ad-Orig-call-interactively function record-flag keys)))
  (let ((ido-ubiquitous-next-override (ido-ubiquitous-get-command-override function))) (setq ad-return-value (with-no-warnings (ad-Orig-call-interactively function record-flag keys))))
  (ido-ubiquitous-with-override (ido-ubiquitous-get-command-override function) (setq ad-return-value (with-no-warnings (ad-Orig-call-interactively function record-flag keys))))
  (let (ad-return-value) (ido-ubiquitous-with-override (ido-ubiquitous-get-command-override function) (setq ad-return-value (with-no-warnings (ad-Orig-call-interactively function record-flag keys)))) ad-return-value)
  call-interactively(haskell-mode-contextual-space nil nil)

Specs

I'm using haskell-mode-20150403.1144 with emacs 24.3.1 onUbuntu 14.04.2 LTS, using ghc 7.8.4 and cabal 1.22.2.0

init.el

Here is the haskell part of my init.el (no ghc-mod currently)

(require 'haskell-mode)
(load "haskell-mode-autoloads")

(eval-after-load 'haskell-mode
  '(progn
     (setq haskell-notify-p t)
     (setq haskell-tags-on-save t)
     (setq haskell-indent-offset 2)))

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

(defun rwl-haskell-hook ()
  (turn-on-haskell-simple-indent)
  (define-key haskell-mode-map (kbd "<return>") 'haskell-simple-indent-newline-same-col)
  (define-key haskell-mode-map (kbd "C-<return>") 'haskell-simple-indent-newline-indent)

  ;; Taken from Troels / haskell-mode example
  ;; Contextually do clever things on the space key, in particular:
  ;;   1. Complete imports, letting you choose the module name.
  ;;   2. Show the type of the symbol after the space.
  (define-key haskell-mode-map (kbd "SPC") 'haskell-mode-contextual-space)

  ;; Jump to the imports. Keep tapping to jump between import
  ;; groups. C-u f8 to jump back again.
  (define-key haskell-mode-map [f8] 'haskell-navigate-imports)

  ;; Indent the below lines on columns after the current column.
  (define-key haskell-mode-map (kbd "C-S-<right>")
    (lambda ()
      (interactive)
      (haskell-move-nested 1)))
  ;; Same as above but backwards.
  (define-key haskell-mode-map (kbd "C-S-<left>")
    (lambda ()
      (interactive)
      (haskell-move-nested -1)))

  (interactive-haskell-mode t))

[gracjan]

@RasmusWL: thanks for the report.

As I see contetual space tries to do :info on the symbol it finds, except it find an empty symbol. What is the thing just before the space?

[RasmusWL]

At least it happens when point is at the beginning of an empty line

[gracjan]

Where does this idea of contextual space come from? There are so much wrong about it:

• for completions Emacs usually uses TAB not space
• it works only when non-obvious conditions are met
• it sometimes pops up Minibuffer, thus space gets into interactive entry mode (when completing import)
• it sometimes does not pop up Minibuffer, just does :info for a near by symbol
• whole thing can just hang due to interactive-haskell being in non-receptive state
• and it will sometimes sort and align the whole import group

And all of that just after a SPACEBAR!

What was the reasoning behind this function?

[gracjan]

@RasmusWL: are you actually trying to use contextual space for something useful or you just enabled it because it was in init.el?

[RasmusWL]

I saw it in the example section on this repo, so I just wanted to try it out. The one time it worked I thought: "oh, that could probably be useful".

[gracjan]

That is what I thought. Contextual space is a nice idea and I'm afraid that inner workings of interactive-haskell-mode are not a solid enough foundation to provide such functionality.

[RasmusWL]

So what is going to happen to it then?

[gracjan]

Very good question. I do not advice using or binding this function to any key until somebody steps up and fixes it.