RosettaCodeData/Task/Balanced-brackets/Elena/balanced-brackets.elena

// Generate a string with N opening brackets ("[") and 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.

import system'routines;
import extensions;
import extensions'text;

randomBrackets(len)
{
   if (0 == len)
   {
      ^emptyString
   }
   else
   {
      var brackets :=
         Array.allocate(len).populate::(i => $91)
         +
         Array.allocate(len).populate::(i => $93);

      brackets := brackets.randomize(len * 2);

      ^ brackets.summarize(new StringWriter()).toString()
   }
}

extension op
{
   get isBalanced()
   {
      var counter := new Integer(0);

      self.seekEach::(ch => counter.append((ch==$91).iif(1,-1)) < 0);

      ^ (0 == counter)
   }
}

public program()
{
   for(int len := 0; len < 9; len += 1)
   {
      var str := randomBrackets(len);

      console.printLine("""",str,"""",str.isBalanced ? " is balanced" : " is not balanced")
   };

   console.readChar()
}