Task:

 Generate a string with   N   opening brackets   [   and with   N   closing brackets   ],   in some arbitrary order. 
 Determine whether the generated string is balanced; that is, whether it consists entirely of pairs of opening/closing brackets (in that order), none of which mis-nest.


Examples

   (empty)      OK
   []           OK   
   [][]         OK   
   [[][]]       OK 
   ][         NOT OK
   ][][       NOT OK
   []][[]     NOT OK



sub check_brackets(s$)
    local level, i
 
    for i = 1 to len(s$)
        switch mid$(s$, i, 1)
            case "[": level = level + 1 : break
            case "]": level = level - 1 : if level < 0 break 2
        end switch
    next i
    return level = 0
end sub
 
s$ = "[[]][]"
 
print s$, " = ";
 
if not check_brackets(s$) print "not ";
print "ok"