PCM completion word boundaries

[Leo]

Hello,

1. customise (using the custom interface) completion-pcm-word-delimiters
   to include > as word boundary,

2. (defun string->symbol ())

3. In an emacs-lisp-mode buffer, type string-symbol M-TAB

It says no match. I wonder if it should match in this case. For example
minibuffer-bitset M-TAB completes to minibuffer--bitset.

The reason I am including > is that in scheme there are tons of
functions with -> in it. > is a bit slower to type and would be great if
I can avoid it using completion.

Thanks.

Leo