How to stop emacs from replacing underbar with <- in ess-mode

Question

ess-mode is \"Emacs speaks statistics.\" This mode is useful for editing programs for R or Splus (two separate statistics packages).

In my buffer, when

Answer 1

Like Michał Marczyk and this R mailing list thread suggested, add this line to ~/.emacs:

(ess-toggle-underscore nil)

Then reload it with M-x load-file and type ~/.emacs.

But if you load the file again, e.g. if you add another customization, then it toggles it back to the original state. So toggle it twice, the first one forcing it to the default:

(ess-toggle-underscore t)
(ess-toggle-underscore nil)

That being said, I like Drummermean's solution better, but it also reverts back to default if you add it to ~/.emacs and load it twice. So force a toggle to the default before:

(ess-toggle-underscore t)
(global-set-key (kbd "M--")  (lambda () (interactive) (insert " <- ")))
(ess-toggle-underscore nil)

I bound the smart assignment to Opt-[minus] like RStudio (on a Mac).