Optional values, flattened and summed

#!ek9
defines module site.collectionTypes.optional

  defines program

    ShowOptionalType()
      stdout <- Stdout()

      //Example with a fully qualified declaration
      maybeInteger as Optional of Integer: Optional() of Integer

      //Nothing will be output
      cat maybeInteger > stdout

      //A type inferred declaration
      item1 <- Optional(5)
      cat item1 > stdout

      //two different ways of checking if optional has a value
      require item1.iterator().hasNext()
      require item1?

      //read as List of (Optional of Integer)
      //fully qualified declaration
      emptyOptionals as List of Optional of Integer: List() of Optional of Integer
      require emptyOptionals is empty

      //type inference mechanism - much more terse
      aListOfOptionals <- List(maybeInteger)
      aListOfOptionals += item1
      aListOfOptionals += Optional(14)

      //But could have been defined like this
      someOptionals <- [maybeInteger, item1, Optional(14)]
      require length someOptionals == 3

      //Use of flatten to get the items out of the optional
      cat aListOfOptionals | flatten > stdout

      //Calculate the sum of the integers.
      sum <- cat aListOfOptionals | flatten | collect as Integer
      require sum == 19

      //Also possible to use an iterator if you wish

      while iter <- item1.iterator() then iter?
        stdout.println(`Value [${iter.next()}]`)

5
5
14
Value [5]