function mymatch(str)
  local _, _, ok, oreveal = str:find("^(ok%f[%A]);?(.*)$")
  if ok == nil then
  	_, _, ok, oreveal = str:find("^(cancel%f[%A]);?(.*)$")
  end
  if oreveal == "" then
  	oreveal = nil
  end
  return ok, oreveal
end

-- this is what I want
print(mymatch("ok")) -- ok nil
print(mymatch("cancel")) -- cancel nil
print(mymatch("ok;domatch")) -- ok domatch
print(mymatch("okdontmatch")) -- nil nil