[opam-devel] [Caml-list] Setting up OPAM in emacs

Gabriel Scherer gabriel.scherer at gmail.com
Sat Jun 15 13:07:51 BST 2013

I don't (want to) understand the details of why opam switches don't
work well with Emacs right now, or of any of the proposed solutions.
Is there a solution integrated in OPAM by now? If not, is there a
consensus on what simple users like me should use to solve the
problem? Could you (the thread participants) decide on something, and
send that to the OPAM upstream, so that future versions solve this

(The immediate problem I observe is that compile-command does not use
the OCaml versions I would expect it to, in general defaulting to my
system OCaml -- that may depend on the way Emacs is launched. More
sophisticated things such as being able to call "opam switch" from
inside Emacs are probably secondary needs, and I would be fine with a
basic integration not supporting that, and letting people hone their
emacs-lisp skills for that.)

On Tue, Jun 4, 2013 at 4:55 PM, Leo White <lpw25 at cam.ac.uk> wrote:
> My personal solution for Tuareg mode is to put:
>   ;; Use OPAM's ocaml
>   (setq tuareg-interactive-program "opam config exec ocaml")
> in my .emacs.
> Regards,
> Leo
> Wojciech Meyer <wojciech.meyer at gmail.com> writes:
>> Christophe's function hook is probably much better and elegant solution,
>> but this works for me:
>> (defun dm-opam-switch-root (ocaml-version opam-root)
>>   (interactive "sOCaml version: \nsOPAM root: ")
>>   (let* ((path (if (string-match "\\.opam" (car exec-path)) (cdr exec-path) exec-path))
>>          (entry
>>           (replace-regexp-in-string
>>            "\n" ""
>>            (shell-command-to-string
>>             (format "opam switch --root %s %s > /dev/null && opam config env | sed -n 's/^PATH=\\([^:]\\+\\):.*$/\\1/p'" opam-root ocaml-version))))
>>          (env-path (replace-regexp-in-string "\n" "" (shell-command-to-string (format "opam config env --root %s | sed -n 's/^PATH=\\(.*\\)/\\1/p'" opam-root)))))
>>     (setq exec-path (cons entry path))
>>     (setenv "PATH" env-path)))
>> (defun dm-opam-switch (ocaml-version)
>>   (interactive "sOCaml version: ")
>>   (dm-opam-switch-root ocaml-version "~/.opam"))
>> <<
>> I wouldn't say myself it's a perfect script, but it works. Note that I
>> use a lot of shell trickery instead of Emacs buffers, which is probably
>> not a good idea.
>> You just say M-x dm-opam-switch, and indicate which version you would
>> like.
>> Best,
>> Wojciech
>> Christophe TROESTLER <Christophe.Troestler at umons.ac.be> writes:
>>> On Tue, 28 May 2013 09:59:53 +0400, Ivan Gotovchits wrote:
>>>> 2. Use «eval `opam env config`» in the begining of a compile-command.
>>>>    This works fine when you switch compiler, but other commands, such as
>>>>    «C-c C-s» doesn't use new environment.
>>> I use this for the compilation:
>>>     ;; OPAM compilation — one must update to the current compiler
>>>     ;; before launching the compilation.
>>>     (defadvice compile (before compile-opam activate)
>>>       "Run opam to update environment variables"
>>>       (set (make-local-variable 'compilation-environment)
>>>         (with-temp-buffer
>>>           (ignore-errors (call-process "opam" nil t nil "config" "-env"))
>>>           (goto-char (point-min))
>>>           (while (re-search-forward "; *export.*$" nil t)
>>>             (replace-match "" nil nil))
>>>           (split-string (buffer-substring 1 (point-max)))
>>>           )))
>>> For the toplevel, I am afraid one needs to restart it.  I guess a
>>> similar trick is possible to automatically select the right one.
>>> Hope it helps,
>>> C.
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