prettify-symbols-mode enabled for major mode, but ligatures don't show until toggling prettify on and off

Question

I'm pretty new to emacs and giving it a shot because it seems to be much better integrated with the OCaml tool chain than any other editor.

Since OCaml uses a lot of symbols, I want to enable ligature support.

If it's relevant, I'm using spacemacs. Here's what I've added to my dotspacemacs/user-config()

  (load "~/.emacs.d/private/local/pragmatapro-prettify-symbols-v0.828.el")
  (add-hook 'tuareg-mode-hook #'prettify-hook)
  (global-prettify-symbols-mode t)

The .el file I'm using is available here for reference and defines prettify-hook.

The strange thing is that after opening a .ml file in Tuareg mode, I can see that prettify-symbols-mode is active, but none of the symbols are converted to ligatures. However, if I toggle prettify-symbols-mode off and then back on, the symbols render correctly.

Has anyone else had this issue or have any ideas how I can get it to work automatically upon opening a the file?

Edit:

So, interestingly enough, after looking again it seems like some sort of symbol replacement is happening, but it isn't happening with the correct glyphs or for all of the patterns defined in the .el file. For example <= is replaced with a reasonable, but incorrect glyph; |> is not replaced at all. After toggling the mode I end up with the correct replacement glyphs.

See the answers section for the solution I came up with.

Answer 1

I came up with a working solution after fiddling around and figuring out the information I edited into the original question. I'm not sure if this is the best approach, but it resolved my issue.

After these changes the correct ligatures are displayed within OCaml's Tuareg mode automatically.

First, I deleted

  (global-prettify-symbols-mode t)

from my config file. I'm not 100% sure if this is necessary, but since I only want ligatures in Tuareg mode it seemed cleaner not to enable them globally.

Secondly, I added a function to toggle prettify-symbols-mode off and on in the .el file I linked above and added it to the prettify-hook that runs when Tuareg mode is activated. I'm still not sure why this is necessary, but it does the trick.

(defun refresh-pretty ()
  (prettify-symbols-mode -1)
  (prettify-symbols-mode +1))

;; main hook fn
(defun prettify-hook ()
  (add-pragmatapro-prettify-symbols-alist)
  (setup-compose-predicate)
  (refresh-pretty))

Answer 2

I have the same problem, and I'm not sure if this is the correct way to work with it, but it does work for me.

I believe the problem is one of hook order. Because prettify-symbols-alist is buffer local, you either have to setq-default it or have it set via some hook when a buffer is opened. The latter should be the preferred way to do it, as different languages have different ideas of what symbols mean; you probably don't want "and" rendered as "∧" in text-mode.

So, given that:

1. prettify-symbols-alist is buffer-local (ideally), and,
2. prettify-symbols-mode only looks at prettify-symbols-alist once, when it starts

you have to ensure that step 1 happens before step 2.

I have two solutions:

1. Use (global-prettify-symbols-mode 1) in your .emacs (or equivalent). Then set up the prettify-symbols-alist in your programming hook:

(defun bjc/lisp-mode-hook ()
  "Hook when entering ‘lisp-mode’."
  (mapc (lambda (elt) (push elt prettify-symbols-alist))
        '(("<=" . ?≤)
          (">=" . ?≥)
          ("and" . ?∧)
          ("or" . ?∨)
          ("xor" . ?⊕)
          ("->" . ?→)
          ("<-" . ?←))))

(global-prettify-symbols-mode 1)
(add-hook 'emacs-lisp-mode-hook 'bjc/lisp-mode-hook)

2. Arrange to have prettify-symbols-mode called after your particular major mode hook. The easiest way to do this is to simply call it from the hook that sets up prettify-symbols-alist:

(defun bjc/lisp-mode-hook ()
  "Hook when entering ‘lisp-mode’."
  (mapc (lambda (elt) (push elt prettify-symbols-alist))
        '(("<=" . ?≤)
          (">=" . ?≥)
          ("and" . ?∧)
          ("or" . ?∨)
          ("xor" . ?⊕)
          ("->" . ?→)
          ("<-" . ?←)))

  (prettify-symbols-mode 1))

Personally, I've gone with the former, because it seems cleaner to me, but YMMV.