match regexp to list elements

[evan]

Hi all, I want to locate all elements of a list that match a regexp.
Say I want to write the function match-list-regexp such as if
my-list = '(a1 b2 a3 b4)
then
(match-list-regexp "a[0-9]" my-list)
should give '(0 2)

I though I could use function string-match but I need a way of
converting the elements of a list into strings. Any ideas?
Thanks.
Evan.