Format SML source code using smlfmt. Requires reformatter.el, on top of which this package is a very small number of lines of code.

With use-package:

(use-package smlfmt
 :hook (sml-mode . smlfmt-format-on-save-mode)
 :bind
 (:map sml-mode-map
   ("C-c r" . smlfmt-format-buffer)))

• Or just load-file the smlfmt.el file.

• Or add its directory to your load-path and (require 'smlfmt).

The package can be configured via the usual customize-group RET smlfmt mechanism.