function add(integer a, integer b)
    return a + b
end function

function sub(integer a, integer b)
    return a - b
end function

function mul(integer a, integer b)
    return a * b
end function

function reduce(integer rid, sequence s)
object res = s[1]
    for i=2 to length(s) do
        res = call_func(rid,{res,s[i]})
    end for
    return res
end function

?reduce(routine_id("add"),tagset(5))
?reduce(routine_id("sub"),tagset(5))
?reduce(routine_id("mul"),tagset(5))