mm1sim <- function() {
   initglbls()
   # create simulation
   newsim()
   # get things going, generating and scheduling first arrival event
   arvtime <- rexp(1,rate=arvrate)
   schedevnt(arvtime,arvtype,arvtime)
   mainloop(10000.0)
   return(totwait/njobsdone)
}

# application:  M/M/1 queue, arrival rate 0.5, service rate 1.0; we must
# set the globals and the function reactevnt() for this application

# initializes the global variables
initglbls <- function() {
   # globals
   # rates
   arvrate <<- 0.5  # arrival rate
   srvrate <<- 1.0  # service rate
   # event types
   arvtype <<- 1  # arrival type
   srvdonetype <<- 2  # service done type
   # server queue, consisting of arrival times of queued jobs
   srvq <<- vector(length=0) 
   # statistics
   njobsdone <<- 0  # jobs done so far
   totwait <<- 0.0  # total wait time so far
}

# application-specific event processing function required by mainloop()
# in the general DES library above
reactevnt <- function(head) {
   if (head[2] == arvtype) {  # arrival
      # if server free, start service, else add to queue
      if (length(srvq) == 0) {
         srvq <<- head[3]
         srvdonetime <- sim$currtime + rexp(1,srvrate)
         schedevnt(srvdonetime,srvdonetype,head[3])
      } else srvq <<- c(srvq,head[3])
      # generate next arrival
      arvtime <- sim$currtime + rexp(1,arvrate)
      schedevnt(arvtime,arvtype,arvtime)
   } else {  # service done
      # process job that just finished
      # do accounting
      njobsdone <<- njobsdone + 1
      totwait <<- totwait + sim$currtime - head[3] 
      # remove from queue
      srvq <<- srvq[-1]
      # more still in the queue?
      if (length(srvq) > 0) {
         # schedule new service
         srvdonetime <- sim$currtime + rexp(1,srvrate)
         schedevnt(srvdonetime,srvdonetype,srvq[1])
      }
   }
}