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

Summary

dir - is a sub-type of type stream. Provides a stream abstraction of dir.

stream - an abstract type
The sub-types of this type needs to provide the implementations for read,seek,tell,open close.
presently provides the for-each implementation.
         

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