Emacs has the wonderfull "inferior tcl" process which allows us to
start Tcl in an Emacs window.  Unfortunately, this doesn't work
automatically on Windows, Emacs is unable to make the Tcl interpreter
start in the "interactive" mode.  The problem is that Tcl calls istty()
to determine whether tcl_interactive
[http://tcl.activestate.com/man/tcl8.4/UserCmd/tclsh.htm#M10] should be
set and whether prompts should be displayed.  But the Windows version of
Emacs can not make istty() return the right value so this doesn't happen
and tclsh thinks it's running non-interactive.

One solution is to change the tclsh code, but not everyone can or wants
to do that.  Another solution is to simulate the command loop in pure
Tcl.  This works without any changes to Tcl or Emacs, so here is the
code that I currently use:

 namespace eval CmdInput {

	# We want to allow shell commands to be executed automatically
	# as in normal interactive use.  The "unknown" proc checks
	# that "info script" returns "", before it enables that
	# behaviour, so we subclass "info".  In Tcl 8.4 we could simply
	# call 'info script ""' I believe, but 8.3 and earlier don't do
	# that.
	variable this_script [info script]
	proc info {args} {
		set result [uplevel [concat __org_info $args]]
		set cmd [lindex $args 0]

		variable this_script
		if {"script" == $cmd && "$result" == $this_script} {
			return ""
		} else {
			return $result
		}
	}
	rename ::info ::__org_info ;# using a namespace proc here cores
	proc ::info {args} "uplevel \[concat [namespace which info] \$args\]"

	proc loop {} {
		# preparations
		fconfigure stdin  -buffering line
		fconfigure stdout -buffering line
		fconfigure stderr -buffering line
		set ::tcl_interactive 1

		if {[file exists ~/tclshrc.tcl]} {
			namespace eval :: {uplevel \#0 source ~/tclshrc.tcl}
		}

		# input loop
		while {1} {
			catch {uplevel \#0 $::tcl_prompt1}
			flush stdout
			set cmd {}
			while {1} {
				append cmd [gets stdin] "\n"
				if {[info complete $cmd]} {
					break
				}
				catch {uplevel \#0 $::tcl_prompt2}
				flush stdout
			}
			history add $cmd
			catch {uplevel \#0 $cmd} result
			puts $result
		}
		return ""
	}
 }

 catch {CmdInput::loop} result 
 puts $result
 exit 0


To use this code: Save it to a file called cmd-input.tcl.  In Emacs
customize the variable tcl-application to read "tclsh83.exe"
and the variable tcl-command-switches to include
"c:/your-path-here/cmd-input.tcl" (this is with Emacs 21.1, Emacs 20 used
other names for the variables, I believe).

I hope this is clear, if not or if you have ideas for improvement, you
can always contact me at mailto:Benjamin.Riefenstahl@epost.de .

----
Note: [Jim Graham] has a similar thing called interp.tcl on his homepage [http://www.gnt.net/~n5ial/tcl].