How do I output stream results to stdout or a collection in EK9?

  > stdout          sends each item to stdout (like Unix > redirect)
  > myList          REPLACES the contents of a List, Set, Dict, PriorityQueue or JSON array with the stream's items (Unix > clobbers; a PriorityQueue keeps its comparator and size limit; a JSON object is replaced by the streamed objects merged into a fresh one)
  >> myList         ADDS the stream's items to what the collection already holds (Unix >> appends; a JSON object is merged into)
  > total           REPLACES a scalar (Integer, Float, String ...) with what the stream produces; >> total adds to it
  collect as Type   materializes stream into new collection
  > file.output()   CLOBBERS the file; >> file.output() APPENDS to it (println a header first, then use >>)

  cat items
    | filter by isValid
    > stdout
  cat numbers
    | sort by ascending
    | head 5
    > stdout
  upper <- cat names
    | map with toUpperCase
    | collect as List of String

  stdout <- cat items | filter by isValid   WRONG — do not use <- for stream output
  result = cat items | collect               WRONG — use 'collect as Type'

#!ek9
defines module qa.streams.outputpatterns

  defines function

    <?-
      Check if a number is even.
    -?>
    isEven() as pure
      -> numberToCheck as Integer
      <- rtn as Boolean: numberToCheck mod 2 == 0

  defines program

    StreamOutputDemo()
      stdout <- Stdout()

      // > stdout — sends each item to standard output
      stdout.println("Even numbers:")
      cat [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
        | filter by isEven
        > stdout

      // collect as — materializes into a new collection
      stdout.println("Collected evens:")
      evens <- cat [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
        | filter by isEven
        | collect as List of Integer
      stdout.println($evens)

      // head N — take first N then > to sink
      stdout.println("First 3:")
      cat [10, 20, 30, 40, 50]
        | head 3
        > stdout