# Read below to understand these 2 functions
proc readit {chan} {
    gets $chan data
    puts "We read $data from the socket."
}

proc writeit {chan} {
    # Now we can write something to the socket safely.
    puts $chan "Some data"
}

proc Serve {chan host port} {
   puts "IP $host connected through port $port on channel $chan."
   # Here is the interesting part. We set an event to the socket, and when it's readbale it'll execute the readit function and pass the channel as arg.
   fileevent $chan readable {readit $chan}
   fileevent $chan writable {writeit $chan}
}

# The line below creates a socket server and transfers control to the callback function
socket -server Serve 1234
# The line below waits in a infinite loop (only needed for console app)
vwait forever