function check_brackets(sequence s)
integer level = 0
    for i=1 to length(s) do
        switch s[i]
            case '[': level += 1
            case ']': level -= 1
                      if level<0 then exit end if
        end switch
    end for
    return (level=0)
end function

sequence s
constant ok = {"not ok","ok"}

for i=1 to 10 do
    for j=1 to 2 do
        s = shuffle(join(repeat("[]",i-1),""))
        printf(1,"%s %s\n",{s,ok[check_brackets(s)+1]})
    end for
end for