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Remote agent/Agent interface

From Rosetta Code
Remote agent/Agent interface is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.
In Remote agent, a component is described that marshals commands and events between a stream and a program that issues commands and processes the resulting events. Using the protocol definition described there, build this component in a fashion idiomatic and natural to your language.


See Remote agent/Simulation/C


package ifc
// Streamer interface type defines how agent and world talk to each other.
// Send and Rec may be implemented as synchronous blocking operations.
// They can be considered perfectly reliable as there is no acknowledgement
// or timeout mechanism.
type Streamer interface {
Rec() byte
// The agent and world send and receive single bytes, out of the set of
// constants defined here.
const Handshake = 'A'
const (
CmdForward = '^'
CmdRight = '>'
CmdLeft = '<'
CmdGet = '@'
CmdDrop = '!'
EvGameOver = '+'
EvStop = '.'
EvColorRed = 'R'
EvColorGreen = 'G'
EvColorYellow = 'Y'
EvColorBlue = 'B'
EvBallRed = 'r'
EvBallGreen = 'g'
EvBallYellow = 'y'
EvBallBlue = 'b'
EvBump = '|'
EvSectorFull = 'S'
EvAgentFull = 'A'
EvNoBallInSector = 's'
EvNoBallInAgent = 'a'

Above is the interface package defining the abstract interface. Below is an example of a driver program that supplies a concrete implementation of the interface. This implementation uses Go channels to run a simulation in a single process. A different implementation might produce two executables that would run on different processes or different machines. It would use the same interface however.

package main
import (
// Concrete type chanStreamer implements interface ifc.Streamer.
// Implementaion is with channels, a simple way to demonstrate concurrency.
type chanStreamer struct {
name string
in <-chan byte
out chan<- byte
// Send satisfies ifc.Streamer.Send method.
func (c chanStreamer) Send(b byte) {
log.Print(, " sends ", text[b])
c.out <- b
// Rec satisfies ifc.Streamer.Rec method.
func (c chanStreamer) Rec() byte {
b := <
log.Print(, " recieves ", text[b])
return b
func main() {
// Logging is done with the log package default logger, so this is
// technically something that might be shared by the agent and the world.
// Currently though, the agent doesn't do anything with the logger, only
// the world does.
// Create channels for chanStreamer. Only two channels are needed,
// cmd going from agent to world, and ev going from world to agent.
cmd := make(chan byte)
ev := make(chan byte)
// Instantiate chanStreamer for agent and start agent as a goroutine.
// This allows it to run concurrently with the world.
go agent.Agent(chanStreamer{"agent", ev, cmd})
// World doesn't need another goroutine, it just takes over main at this
// point. The program terminates immediately when World returns.
world.World(chanStreamer{"world", cmd, ev})

A separate file, but still part of the driver, contains human readable text for commands and events. Alternatively, this file could be included with the interface package for maintainability, but technically it is not a required part of the abstract interface used by the agent and world simulator.

package main
import "ra/ifc"
// Human readable text for commands and events.
var text = map[byte]string{
ifc.CmdForward: "command forward",
ifc.CmdRight: "command turn right",
ifc.CmdLeft: "command turn left",
ifc.CmdGet: "command get",
ifc.CmdDrop: "command drop",
ifc.EvGameOver: "event game over",
ifc.EvStop: "event stop",
ifc.EvColorRed: "event color red",
ifc.EvColorGreen: "event color green",
ifc.EvColorYellow: "event color yellow",
ifc.EvColorBlue: "event color blue",
ifc.EvBallRed: "event ball red",
ifc.EvBallGreen: "event ball green",
ifc.EvBallYellow: "event ball yellow",
ifc.EvBallBlue: "event ball blue",
ifc.EvBump: "event bump",
ifc.EvSectorFull: "event sector full",
ifc.EvAgentFull: "event agent full",
ifc.EvNoBallInSector: "event no ball in sector",
ifc.EvNoBallInAgent: "event no ball in agent",


The interface logic for the PicoLisp solution is directly integrated into the client Remote agent/Agent logic#PicoLisp.


Works with: Tcl version 8.6
package require Tcl 8.6
oo::class create AgentAPI {
variable sock events sectorColor ballColor
constructor {host port} {
set sock [socket $host $port]
fconfigure $sock -buffering none -translation binary -encoding ascii \
-blocking 0
# Hack to allow things to work in 8.6b1 and 8.6b2
if {![llength [info commands yieldto]]} {
interp alias {} yieldto {} ::tcl::unsupported::yieldTo
coroutine ReaderCoroutine my ReadLoop
destructor {
if {[llength [info command ReaderCoroutine]]} {
rename ReaderCoroutine {}
if {[llength [info command AgentCoroutine]]} {
rename AgentCoroutine {}
if {$sock ne ""} {
catch {close $sock}
method Log message {
# Commands
method ForwardStep {} {
my Log "action: forward"
puts -nonewline $sock "^"
my ProcessEvents [yield]
method TurnRight {} {
my Log "action: turn right"
puts -nonewline $sock ">"
my ProcessEvents [yield]
method TurnLeft {} {
my Log "action: turn left"
puts -nonewline $sock "<"
my ProcessEvents [yield]
method GetBall {} {
my Log "action: get ball"
puts -nonewline $sock "@"
my ProcessEvents [yield]
method DropBall {} {
my Log "action: drop ball"
puts -nonewline $sock "!"
my ProcessEvents [yield]
method ProcessEvents {events} {
set sectorColor {}
set ballColor {}
set err {}
set done 0
foreach e $events {
my Log "event: $e"
switch [lindex $e 0] {
sector {set sectorColor [lindex $e 1]}
ball {set ballColor [lindex $e 1]}
error {set err [lindex $e 1]}
gameOver {set done 1}
if {$err ne ""} {throw $err "can't do that: $err"}
return $done
# Event demux
method ReadLoop {} {
# Init handshake
fileevent $sock readable [info coroutine]
while 1 {
if {[read $sock 1] eq "A"} break
puts -nonewline $sock "A"
# Main loop; agent logic is in coroutine
try {
coroutine AgentCoroutine my Behavior
while 1 {
set ch [read $sock 1]
switch $ch {
"." {
# Stop - end of events from move
set e $events
set events {}
yieldto AgentCoroutine $e
if {"gameOver" in $e} break
"+" {lappend events gameOver}
"R" {lappend events {sector red}}
"G" {lappend events {sector green}}
"Y" {lappend events {sector yellow}}
"B" {lappend events {sector blue}}
"r" {lappend events {ball red}}
"g" {lappend events {ball green}}
"y" {lappend events {ball yellow}}
"b" {lappend events {ball blue}}
"|" {lappend events {error bumpedWall}}
"S" {lappend events {error sectorFull}}
"A" {lappend events {error agentFull}}
"s" {lappend events {error sectorEmpty}}
"a" {lappend events {error agentEmpty}}
} finally {
close $sock
set sock ""
method Behavior {} {
error "method not implemented"
# Export as package
package provide RC::RemoteAgent 1