define BinarySearch(A, value);
    define do_it(low, high);
        if high < low then
            return("not_found");
        endif;
        (low + high) div 2 -> mid;
        if A(mid) > value then
            do_it(low, mid-1);
        elseif A(mid) < value then
            do_it(mid+1, high);
        else
            mid;
        endif;
    enddefine;
    do_it(1, length(A));
enddefine;