How can I get the :regexp property for abbrev to work?

Question

I have a local abbrev table set up in a file. I have an abbrev that has the "+" character. By default, abbrev will not expand this abbrev because it sees "+" as a word boundary.

The docs say this can be resolved with the :regexp property.

I tried it out. Consider this setup:

(set-local-abbrevs '(
             ("mse" "mean square error" nil)
             ("wlog" "without loss of generality" nil)
             ("++" "\\+" nil)
             ))

(defvar my-abbrev-regexp
  "\\([[:word:]]+\\)"
  ;; "\\([0-9A-Za-z._-]+\\)"
  "")

(abbrev-table-put local-abbrev-table :regexp  my-abbrev-regexp)
(abbrev-mode)

Let's for a minute forget the abbrev with the "+" character and try to expand "wlog". If I comment out the abbrev-table-put line, it expands it just fine when I press SPC. If I uncomment it, then I cannot get "wlog" to expand. I tried both regular expressions shown, both with and without the "+" quantifier.

I also tried the suggested solution here, adding the "<" character to the regexp, and it still doesn't expand.

Edit: Apparently set-local-abbrevs is a custom function I had in my config, taken from the Emacs Wiki. It creates a local abbrev table. Below is the definition.

(defun set-local-abbrevs (abbrevs)
    "Add ABBREVS to `local-abbrev-table' and make it buffer local.
     ABBREVS should be a list of abbrevs as passed to `define-abbrev-table'.
     The `local-abbrev-table' will be replaced by a copy with the new 
     abbrevs added, so that it is not the same as the abbrev table used
     in other buffers with the same `major-mode'."
    (let* ((bufname (buffer-name))
           (prefix (substring (md5 bufname) 0 (length bufname)))
           (tblsym (intern (concat prefix "-abbrev-table"))))
      (set tblsym (copy-abbrev-table local-abbrev-table))
      (dolist (abbrev abbrevs)
          (define-abbrev (eval tblsym)
            (car abbrev)
            (cadr abbrev)
            (caddr abbrev)))
    (setq-local local-abbrev-table (eval tblsym))))

I'll examine the definition in detail later, but a quick glance isn't finding an obvious cause for my problems.

Update: OK, Tyler's solution works if I put the string verbatim in abbrev-table-put, but not if I put it in the my-abbrev-regexp variable. Likely the number of backslashes?

Now that I have "wlog" working, I still can't get ++ to expand.My regexp is \\<\\([+[:word:]]+\\). Ideas?