A 21st Century IDE
Merlin, Tuareg and ocp-indent

I finally decided to sit down and get the shiny new merlin mode for OCaml working with my emacs configuration. Basically, really rather simple in the end although (in the usual fashion!) I did end up spending considerable time tweaking various other customisations

Most of the information below is based on the following sources:

Before we begin, install merlin:

$ opam install merlin

The complete commit change is in my github account (combined with a large cleanup of various other aborted OCaml configurations). Breaking it down a bit, first setup some paths: where to find ocp-indent, merlin.el for merlin-mode, and the ocamlmerlin command itself. Note that this relies on the current state of opam, so when you start emacs be sure to have selected the opam compiler-switch that you installed the merlin package into, above.

;; ocp-indent
(load-file (concat
            (substring (shell-command-to-string "opam config var prefix") 0 -1)
            "/share/typerex/ocp-indent/ocp-indent.el"
            ))

;; merlin-mode
(push (concat
       (substring (shell-command-to-string "opam config var share") 0 -1)
       "/emacs/site-lisp"
       )
      load-path)

(setq merlin-command
      (concat
       (substring (shell-command-to-string "opam config var bin") 0 -1)
       "/ocamlmerlin"
       ))
(autoload 'merlin-mode "merlin" "Merlin mode" t)

Now the meat: when we select tuareg-mode, use ocp-indent to indent lines, turn on merlin auto-complete, and finally set a couple of local key bindings so that I can fix up merlin to not conflict with my now-neurologically-hardwired navigation keys.

(add-hook 'tuareg-mode-hook
          '(lambda ()
             (merlin-mode)
             (setq indent-line-function 'ocp-indent-line)
             (setq merlin-use-auto-complete-mode t)
             (local-set-key (kbd "C-S-<up>") 'merlin-type-enclosing-go-up)
             (local-set-key (kbd "C-S-<down>") 'merlin-type-enclosing-go-down)
             ))

Finally, do the usual to use tuareg-mode for OCaml/F# editing.

(push'("\\.ml[iylp]?" . tuareg-mode) auto-mode-alist)
(push '("\\.fs[ix]?" . tuareg-mode) auto-mode-alist)

And that’s it!