-- Copyright 1993-1998, by the Cecil Project
-- Department of Computer Science and Engineering, University of Washington
-- See the LICENSE file for license information.


--DOC Stream views of indexed collections are fully positionable, but
--DOC not insertable, extensible, or removable. (Stream views of arrays
--DOC could be made extensible.)

template representation indexed_stream_view[T] isa positionable_stream[T];
  private field contents(@:indexed_stream_view[`T]):indexed[T];
  private var field pos(@:indexed_stream_view[`T]):int := 0;

  method position(v@:indexed_stream_view[`T]):int { v.pos }
  method set_position(v@:indexed_stream_view[`T], p:int, 
		      off_end:&():void):void {
      if(p < 0 | { p > v.length }, off_end, { v.pos := p; });
  }

  method peek_next(v@:indexed_stream_view[`T], at_end:&():T):T {
      fetch(v.contents, v.position, at_end) }
  method peek_prev(v@:indexed_stream_view[`T], at_start:&():T):T {
      fetch(v.contents, v.position.pred, at_start) }

  method length(v@:indexed_stream_view[`T]):int { v.contents.length }

  method view_stream(c@:indexed[`T]):positionable_stream[T] {
      concrete object isa indexed_stream_view[T] { contents := c } }
       

-- also allow mutation

template representation m_indexed_stream_view[T] isa m_positionable_stream[T],
					     indexed_stream_view[T];
  private field signature contents(m_indexed_stream_view[`T]):m_indexed[T];

  method set_peek_next(v@:m_indexed_stream_view[`T], x:T):void { 
      v.contents!v.position := x;
  }
  method set_peek_prev(v@:m_indexed_stream_view[`T], x:T):void { 
      v.contents!v.position.pred := x;
  }

  method view_stream(c@:m_indexed[`T]):m_positionable_stream[T] {
      concrete object isa m_indexed_stream_view[T] { contents := c } }