Can I prevent Mac Mail from converting "--" to "—"?

In Mac Mail, when I'm typing a snippet of Ada code, it oh-so-helpfully converts the "--" character which indicates a comment in Ada code to the "—" symbol. I can undo it, but then if I make adjustments to what I've written, it reconverts it, and I have to undo it again. As you can imagine, this is frustrating. I've read the excellent answer here on how to turn off auto-corrections, but evidently this isn't an auto-correction feature as although I tested that the trick worked for me on "teh", it doesn't work for "--".

Is there any way to turn off this "feature"?