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



matching?:
	swap 0
	for c in chars:
		if = c "]":
			++
		elseif = c "[":
			if not dup:
				drop
				return false
			--
	not
 
!. matching? ""
!. matching? "[]"
!. matching? "[][]"
!. matching? "[[][]]"
!. matching? "]["
!. matching? "][]["
!. matching? "[]][[]"