#line 6 "/home/ubuntu/felix/src/packages/streams.fdoc"
  Class of data structures supporting streaming.
  The container type just needs an iterator method.
  The iterator method returns a generator which
  yields the values stored in the container.
  class Iterable [C1, V] {
    virtual fun iterator : C1 -> 1 -> opt[V];
  }
  
  class Streamable[C1, V] {
    inherit Iterable[C1,V];
  
    // check if a streamable x is a subset of a set y.
    virtual fun \(\subseteq\)[C2 with Set[C2,V]] (x:C1, y:C2) =
    {
      for v in x do
        if not (v \(\in\) y) goto bad;
      done
      return true;
  bad:>
      return false;
    }
  
    // subset or equal: variant equality bar
    fun \(\subseteqq\) [C2 with Set[C2,V], Streamable[C2,V]]
      (x:C1, y:C2) => x \(\subseteq\) y
    ;
  
    // congruence (equality as sets)
    virtual fun \(\cong\)[C2 with Set[C2,V], Streamable[C2,V], Set[C1,V]]
      (x:C1, y:C2) => x \(\subseteq\) y and y \(\subseteq\) x
    ;
  
    // negated congruence
    fun \(\ncong\)[C2 with Set[C2,V], Streamable[C2,V], Set[C1,V]]
      (x:C1, y:C2) => not (x \(\cong\) y)
    ;
  
    // proper subset
    virtual fun \(\subset\) [C2 with Set[C2,V], Streamable[C2,V], Set[C1,V]]
      (x:C1, y:C2) => x \(\subseteq\) y and x \(\ncong\) y
    ;
  
    // variant proper relations with strke-through on equality bar
    fun \(\subsetneq\) [C2 with Set[C2,V], Streamable[C2,V], Set[C1,V]]
      (x:C1, y:C2) => x \(\subset\) y
    ;
    fun \(\subsetneqq\) [C2 with Set[C2,V], Streamable[C2,V], Set[C1,V]]
      (x:C1, y:C2) => x \(\subset\) y
    ;
  
    // reversed relations, super set
    fun \(\supset\) [C2 with Set[C2,V], Streamable[C2,V], Set[C1,V]]
      (x:C1, y:C2) => y \(\subset\) x
    ;
  
    fun \(\supseteq\) [C2 with Set[C2,V], Streamable[C2,V]]
      (x:C1, y:C2) => y \(\subseteq\) x
    ;
  
    fun \(\supseteqq\) [C2 with Set[C2,V], Streamable[C2,V]]
      (x:C1, y:C2) => y \(\subseteq\) x
    ;
    // variant proper relations with strke-through on equality bar
    fun \(\supsetneq\) [C2 with Set[C2,V], Streamable[C2,V], Set[C1,V]]
      (x:C1, y:C2) => x \(\supset\) y
    ;
    fun \(\supsetneqq\) [C2 with Set[C2,V], Streamable[C2,V], Set[C1,V]]
      (x:C1, y:C2) => x \(\supset\) y
    ;
  
  
    // negated operators, strike-through
    fun \(\nsubseteq\) [C2 with Set[C2,V], Streamable[C2,V]]
      (x:C1, y:C2) => not (x \(\subseteq\) y)
    ;
  
    fun \(\nsubseteqq\) [C2 with Set[C2,V], Streamable[C2,V]]
      (x:C1, y:C2) => not (x \(\subseteq\) y)
    ;
  
    // negated reversed operators, strike-through
    fun \(\nsupseteq\) [C2 with Set[C2,V], Streamable[C2,V], Set[C1,V]]
      (x:C1, y:C2) => not (x \(\supseteq\) y)
    ;
  
    fun \(\nsupseteqq\) [C2 with Set[C2,V], Streamable[C2,V], Set[C1,V]]
      (x:C1, y:C2) => not (x \(\supseteq\) y)
    ;
  
  }