''The "rchan" command is now part of [CritLib] [http://www.equi4.com/critlib]''
where it is called "[rechan]".
----
This package defines an "rchan" [command], which lets you create [Tcl]-style
[channel]s that are completely handled by Tcl scripts, instead of [C] code.

The rchan [extension] itself is written in C, and requires [Critcl] to turn it
into an extension (on the fly)

Rchan must be called with two arguments to create a new channel:
    rchan cmd mode

Where:
    cmd = the name of the "callback" that will process requests
    mode = the open mode:
     2 is read only (not thoroughly tested yet)
     4 is write only (not thoroughly tested yet)
     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

Other operations are not supported ([close], for example, so the caller must
keep track of this channel and clean up as appropriate - which is messy).

Rchan is not all that capable, it does not work well with [fileevent]s, and
in general it definitely could use some re-work and modernization.  But it
has been invaluable in [TclKit] to implement its database-backed [VFS] design.

Without some sort of &quot;reflection&quot;, 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.

Nov 2003 status - close is now also tracked, and file-event friendliness is ok now. (This is not new, but as this page appears to have been edited recently, I thought I'd update the facts about it as well) -[jcw]
----
[PWQ] ''19 Feb 05'', surely you jest, ''mode = 2,4,6''?. You really mean 
'''mode = r,w,r+||w+''' do you not?

[Zarutian] 7. mars 2005: it gives an error indicating that it expected an integer but not a char in every instance of r,w,r+||w+. I suspect the interger is treated like a set of binary flags of (to us) an unknown length.

''PWQ'', my comment wasn't a bug report, it was to say '''WTF?, this is TCL not C, we use strings not numbers for parameters.''' That is to say , IMO the code should use string arguments to open and not numbers.

[Zarutian] 4. june 2005: I am as perplexed as you but this is what the command accepts as parameters.

11jun05 [jcw] - Heh, so it took 3 years to expose my craziness, eh? ;) - I'm amazed by this response, actually, since it takes just one line of Tcl to wrap this logic into whatever API you prefer.  Let me reveal a secret: I don't code in C to create a nice Tcl API: I use Tcl for that.  ''This isn't flame bait, but you are welcome to point to the above as proof (at last!) that everything I do is madness <wink>''