Defining a Variable that depends on an unknown number

I am looking for a solution that can define a variable that depends on
an unknown number of conditions.  I'm hoping for a solution
compatibile with XSLT 1.0.

xml file:  in the xml file there can be any number of <option>'s with a value.
<xml>
  <option value="7"/>
  <option value="8"/>
  ...
  <option value="1"/>
</xml>

xsl file: How do I define variable "hasZero" based on these conditions...
  a) if at least one option has value="0", set "hasZero" to "yes"
  b) otherwise "hasZero" is "no".

The only way I can think of doing this is with <xsl:break />, but that
doesn't exits :)

Thank you.

-- 
Andrew Ferk