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



  [ char [ over of 
    swap
    char ] swap of
    join shuffle ]      is bracket$ ( n --> $ )
 
  [ 0 swap witheach
      [ char [ =
        iff 1 else -1 +
        dup 0 < if
          conclude ]
    0 = ]               is balanced ( $ --> b )
 
 
  10 times
    [ 20 i 2 * - times sp
      i bracket$ dup echo$
      say " is "
      balanced not if
        [ say "un" ]
      say "balanced."
      cr ]