def op(acc x)
    if mod(x 2)
        +(acc x)
    else
        acc
    end
end

# generate a list from 1 to n
def range(n)
    def genrec(l limit n)
        if <(n limit)
            @genrec(+(l list(n)) limit +(n 1))
        else
            l
        end
    end
    genrec(list() n 0)
end

# add odd numbers from 0 to 1001
def main()
    display(fold(0 op range(1001)))
end