Ch5, Ex2

a.
Well, In the current implementation, one controller can be associated with one lift only. If we have one controller and every lift send it step(N), controller will keep on moving one lift only. Obviously its a pretty bad idea.

b.

fun {Controller Init}
   Tid={Timer}
   Cid={NewPortObject Init
        fun {$ Msg state(Motor F Lid)}
           case Motor
           of running then
              case Msg
              of stoptimer then
                 {Send Lid 'at'(F)}
                 state(stopped F Lid)
              end
           [] stopped then
              case Msg
              of step(Dest) then
                 if F==Dest then
                    state(stopped F Lid)
                 elseif F < Dest then X=Dest-F in %CHANGED HERE
                    {Send Tid starttimer(5000*X Cid)}
                    state(running F+X Lid)
                 else X=F-Dest in         % F>Dest
                    {Send Tid starttimer(5000*X Cid)}
                    state(running F-X Lid)
                 end
              end
           end
        end}
in Cid end

fun {Lift Num Init Cid Floors}
   {NewPortObject Init
    fun {$ Msg state(Pos Sched Moving)}
       case Msg
       of call(N) then
         {Browse 'Lift '#Num#' needed at floor '#N}
          if N==Pos andthen {Not Moving} then
             {Wait {Send Floors.Pos arrive($)}}
             state(Pos Sched false)
          else Sched2 in
             Sched2={ScheduleLast Sched N}
             if {Not Moving} then
  {Send Cid step(N)} end
                state(Pos Sched2 true)
          end
       [] 'at'(NewPos) then
          {Browse 'Lift '#Num#' at floor '#NewPos}
          case Sched
          of S|Sched2 then
             if NewPos==S then
                {Wait {Send Floors.S arrive($)}}
                if Sched2==nil then
                   state(NewPos nil false)
                else
                   {Send Cid step(Sched2.1)}
                   state(NewPos Sched2 true)
                end
             else  %NOT CHANGED REALLY
                {Browse 'ERROR: this should not happen'}
                {Send Cid step(S)}
                state(NewPos Sched Moving)
             end
          end
       end
    end}
end