/* replace inchr with outchr in str */
chr2chr(str, inchr, outchr)
{
        local s, cond;

        /* convert to series */
        s = charstrs(str);

        /* find inchr in s */
        cond = (s == charstr(inchr));

        /* replace inchr with outchr */
        s = s * not(cond) + cond * charstr(outchr);

        /* convert to string */
        return(strchars(s));
}