Reflecting channels back into Tcl
=================================

  Rev 1.0:  Renamed (used to be called rchan), fixed fileevent timer bugs
  Rev 0.10: Initial release


The http://mini.net/tcl/2514.html page is a good spot to comment on this.

This package defines a "rechan" command, which lets you create Tcl-style
channels that are completely handled by Tcl scripts, instead of C code.

Rechan must be called with two arguments to create a new channel:
    rechan cmd mode

Where:
    cmd = the name of the "callback" that will process requests
    mode = the open mode (6 is R/W, the normal case)

The callback cmd can be one or more words (i.e. a list).  Depending on the
operation, a request name and some args will be tacked on before invoking
it.  The following requests are implemented:

    $cmd seek $chan <offset> ?<seekmode>?
    	called when a "seek $chan <offset> ?<seekmode>?" is done

    $cmd read $chan <count>
    	called when a "read $chan <count>" request is made

    $cmd write $chan <data>
    	called when a "write $chan <data>" request is made

    $cmd close $chan
    	called when the channel is closed

Other operations are not supported.

Rechan is not all that capable, though it works with fileevents now.  It
has been invaluable in TclKit to implement its database-backed VFS design.

Without some sort of "reflection", the Virtual File System (whether the
original one by Matt Newman or the C-based on in the core by Vince Darley)
could not have been implemented.  It is hoped that one day, some sort of
channel reflection becomes part of standard Tcl, and included in the core.