Spacemacs reason-mode layer

config.el

(spacemacs|define-jump-handlers reason-mode)

funcs.el

(defun spacemacs/merlin-locate ()
  (interactive)
  (let ((merlin-locate-in-new-window 'never))
    (merlin-locate)))

(defun spacemacs/merlin-locate-other-window ()
  (interactive)
  (let ((merlin-locate-in-new-window 'always))
    (merlin-locate)))

packages.el

(setq jf-reason-packages
      '(
        company
        ggtags
        helm-gtags
        merlin
        (reason-mode
         :location (recipe
                    :repo "facebook/reason"
                    :fetcher github
                    :files ("editorSupport/emacs/reason-mode.el" "editorSupport/emacs/refmt.el")))
        ))

(defun jf-reason/post-init-company ()
  (when (configuration-layer/layer-usedp 'merlin)
    (spacemacs|add-company-backends
      :backends merlin-company-backend
      :modes merlin-mode
      :variables merlin-completion-with-doc t)))

(when (configuration-layer/layer-usedp 'syntax-checking)
  (defun jf-reason/post-init-flycheck ()
    (spacemacs/enable-flycheck 'merlin-mode)))

(defun jf-reason/post-init-ggtags ()
  (add-hook 'reason-mode-local-vars-hook #'spacemacs/ggtags-mode-enabled))

(defun jf-reason/post-init-helm-gtags ()
  (spacemacs/helm-gtags-define-keys-for-mode 'reason-mode))

(defun jf-reason/init-merlin ()
  (use-package merlin
    :defer t
    :init
    (progn
      (add-to-list 'spacemacs-jump-handlers-reason-mode
                   'spacemacs/merlin-locate)
      (add-hook 'reason-mode-hook 'merlin-mode)
      (setq merlin-completion-with-doc t)
      (spacemacs/set-leader-keys-for-major-mode 'reason-mode
        "cp" 'merlin-project-check
        "cv" 'merlin-goto-project-file
        "eC" 'merlin-error-check
        "en" 'merlin-error-next
        "eN" 'merlin-error-prev
        "gb" 'merlin-pop-stack
        "gG" 'spacemacs/merlin-locate-other-window
        "gl" 'merlin-locate-ident
        "gi" 'merlin-switch-to-ml
        "gI" 'merlin-switch-to-mli
        "go" 'merlin-occurrences
        "hh" 'merlin-document
        "ht" 'merlin-type-enclosing
        "hT" 'merlin-type-expr
        "rd" 'merlin-destruct)
      (spacemacs/declare-prefix-for-mode 'reason-mode "mc" "compile/check")
      (spacemacs/declare-prefix-for-mode 'reason-mode "me" "errors")
      (spacemacs/declare-prefix-for-mode 'reason-mode "mg" "goto")
      (spacemacs/declare-prefix-for-mode 'reason-mode "mh" "help")
      (spacemacs/declare-prefix-for-mode 'reason-mode "mr" "refactor"))))

(defun jf-reason/init-refmt ()
  (add-hook 'reason-mode-hook (lambda ()
                                (add-hook 'before-save-hook 'refmt-before-save)
                                (merlin-mode)))
  )

(defun jf-reason/init-reason-mode ()
  (use-package reason-mode
    :mode (("\\.re[i]?$" . reason-mode))
    :defer t
    :init
    (setq opam (substring (shell-command-to-string "opam config var prefix 2> /dev/null") 0 -1))
    (setq merlin-ac-setup t)
    )
  )