This page has some type implementations in the framework mentioned in [OO libraries].

'''Summary'''

   stream:   an abstract type.
   dir:   is a subtype of type stream. Provides a stream abstraction of dir. Provides open, close, read, seek, tell methods.
   tell:   gives present position.
   seek:   moves the position.
   read:   item in present position and position is advanced.

The subtypes of this type need to provide the implementations for open, close, read, seek, tell.
It presently provides  [foreach] implementation.

 foreach - foreach <obj> <picked_item> <block to act on picked item>
         

'''Usage'''
 dir create a /tmp # object creation
 > read a          # reads the current item in the stream 
 > foreach a item { puts $item }  # foreach is the iterator for the stream items.

Modified proc ">"
 proc > { args } {
  set obj [lindex $args 1 ]
  upvar $obj myobj
   set handler $myobj(handler)
   set myobj(level) [ expr [info level] - 1 ]
   lvarpop args 1
   lvarpush args myobj 1
   $handler  $args
 }

Type implementations:

Dir - type
 package require Tclx
 proc dir { args } {
    if {! [ string equal [lindex $args 0] create ] } {
     set args [lindex $args 0] 
    }
    set ref [lindex $args 1 ]
    set action [lindex $args 0]
    upvar  $ref myref
    switch $action \
          create {
            array set myref [list handler dir]
            array set myref [list dir [lindex $args 2 ]]
	    array set myref [list items [ glob $myref(dir)/* ] ]
	    array set myref [list position -1 ]
	  } \
	  open {
	    array set myref [list position -1 ]
	  } \
	  read {
	    set pres_elem {}
	    set max_position [ expr [llength $myref(items)] - 1 ]
	    if { $myref(position) < $max_position } {
	     set myref(position) [ expr $myref(position) + 1 ]
	     set pres_elem  [ lindex $myref(items) $myref(position) ]
	    }
	    return $pres_elem

	  } \
	  seek {
	    set index [lindex $args 2 ]
	    if  [ expr $index <  [ llength $myref(items)] ] {
             array set myref [list position [lindex $args 2] ]	
	    }
	  } \
	  tell {
            return $myref(position)
	  } \
	  close {
            array set myref [list position -1 ]	
	  } \
	  default {
	     lvarpop args 1 
	     lvarpush args  myref 1
	     set myargs  $args 
             stream $myargs
	  }

 }

Stream - type
 proc stream { myargs } {
  set args $myargs
  set ref [lindex $args 1 ]
  set action [lindex $args 0]
  upvar  $ref myref
  set handler $myref(handler)

  switch $action \
      foreach {
          $handler {open myref}   
	  while 1  {
              set item [ $handler {read myref} ]
	      if { $item != {} } {
	          upvar $myref(level) [lindex $args 2 ] elem
	          set elem $item
	          uplevel $myref(level) [lindex $args 3 ]
	      } else {
	          break ;
	      }
	  }
      }
 }
----
[Category Object Orientation]