TADS Programming (3) - Daemons

                 Sent in by The Grue

This little bit on TADS will hopefully help explain how to set up
a Daemon and to show just how flexible they can be. Firstly a
Daemon is really nothing more than a counter that increases by a
set amount (normally 1) each time the player takes a move.

Now supposing you had in your game a pedestal and on the pedestal
there is a red rod. If you take the red rod an alarm goes off and
after 6 moves a guard comes in and shoots you. (Isn't life a
bitch). You can call the Daemon anything you like so for this
puzzle we'll call it guardDaemon. (Obvious really).

The first thing you need to do is amend the doTake for the red
rod so when the player takes it, they hear the alarm sound and the
guardDaemon is started.

redrod : item
sdesc = "red rod"
ldesc = "The rod is red"
noun = 'rod'
location = pedestal
doTake (Me) = {
if (redrod.location=pedestal) {"As you lift the rod from the
pedestal, a loud siren begins to wail."; redrod.moveInto(Me);
setDaemon(guardDaemon,true);}
else
{ pass doTake; }
}

Now before we define the complete workings of our Daemon we will
have to add a little bit in the std.t file, under the global
object. We need to add this:

siren = 0
guard = 6

The reason for this is because each Daemon you define has two
local conditions, one of which will be incremented by one each
time the player makes a move.  In our guardDaemon the two local
conditions will be s and g, s for siren and g for guard. The s or
siren is the one that will be incremented and when it equals g or
guard (6 moves) the guard will appear and shoot the player.

Now we can write the routine for our guardDaemon.

guardDaemon :function
{
local s,g;
global.siren:=global.siren +1;
s := global.siren;
g := global. guard;
if (s=g) {"\bA guard rushes through the doorway, lifts a huge
magnum and blows you away";die();}
}
;

That seems ok but what if the player replaces the red rod within
the six moves. We alter the Daemon so it reads...

if (s=g and redrod.location<>pedestal) {"\bA guard rushes through
the doorway, lifts a huge magnum and blows you away;die();}
else
if (s=g and redrod.location=pedestal) {"\bA guard rushes through
the doorway, he notices the red rod is still on the pedestal and
quietly saunters back to the guard room.";}
}
;

Now if the red rod is not on the pedestal after six moves the
player gets shot but if it is on the pedestal the guard will
return to the guard room. This is still not perfect, because
Daemons keep increasing by one all the time, if the player
replaces the red rod and the guard returns to the guard room the
siren condition will be more than 6. The player could then take
the red rod without being shot. To stop this we will reset the
Daemon, so if the siren condition is greater than 6 and the red
rod's location doesn't equal the pedestal, we will make the s or
siren condition = 1, and it will continue to increase.  Once again
when it reaches 6 the player will either be shot or if he has
replaced the rod, the guard will return to the guard room.

This is how to alter your guardDaemon to give the desired effect.

if (s=g and redrod.location<>pedestal) {"\bA guard rushes through
the doorway, lifts a huge magnum and blows you away;die();}
else
if (s=g and redrod.location=pedestal) {"\bA guard rushes through
the doorway, he notices the red rod is still on the pedestal and
quietly saunters back to the guard room.";}
else
if (s>g and redrod.location<>pedestal)
{global.siren:=1;}
}
;




At the moment this Daemon does not really do much towards the
gameplay, as the player can never take the red rod. What you could
do is invent another item in the game, perhaps a red stick and if
the player was to take the red rod and replace it with the red
stick the guard would be fooled and return to the guard room. But
really the thing with Daemons is that you can make them do
virtually anything you want and can also incorporate other
routines within them if you needed to.

This last example will show you how to incorporate a query
function into the guardDaemon.

guardDaemon :function
{
local s,g;
global.siren:=global.siren +1;
s := global.siren;
g := global.guard;
if (s=g and redrod.location<>pedestal) {"A guard rushes through
the doorway, lifts a huge magnum and blows you away";die();}
else if (s=g  and redrod.location=pedestal)
{local yesno;
while (true)
{"A guard rushes through the doorway, he glances over at the
pedestal.  Although the red rod is now back on the pedestal he
still seems a little bit suspicious, he turns to you and says
\"Have you been messing around with that red rod?\"(YES or NO) >";
yesno :=yorn();
if (yesno = 1)
{"The guard can hardly believe your stupidity in owning up, he
quickly slaps a pair of handcuffs upon you and marches you off to
the local jail";
Me.moveInto(jail);incscore(10);exit;}
else if (yesno = 0)
{"\"Oh! my mistake, for a minute I thought someone had been
messing around with the red rod.\" The guard grabs you firmly by
the arm and proceeds to escort you back into the
lobby.";Me.moveInto(lobby);exit;}
}
}
}
;

Now if the siren condition equals the guard condition (6 moves)
and the red red is not on the pedestal the player is shot. If the
Daemon has been started but the player has replaced the red rod
within the 6 moves then the guard will appear and ask the player a
simple question.

The local conditions of s and g have now been made redundant and
the game is now functioning under the local conditions of yesno.
The while true is used so if the player types something other than
a yes or no to answer the guard's question, the question will be
repeated.

If the player responds with a yes, he will be move into the jail
and his score will be increased by 10 pts. If the player responds
no, he will be escorted to the lobby and his score will not
increase. The correct response should be a yes as there is a
prisoner in the jail he needs to talk to.

I have found that with a yesno condition, if you wish the player
to be moved to another location so that they can continue with the
game, you will need to have an 'exit' after the moveInto(room)
command. If you do not put one in you will find the player is
moved to the correct location but the question will still be
repeated. Only if you intend to kill the player off for a certain
response can you leave it out, as all processing of the player's
input will have finished anyway.

                  Till next time

                  IN FROBS WE TRUST!