@Programming Language Tutorial
$ZZT-OOP
$Programming Language Tutorial
$(Extended by bitman)

:top;Contents
!simple;A Simple Example Program
!end;The Importance of #end
!oop;Object Oriented Programming
!flags;Using Flags
!hyper;Hypertext Messages

     The best way to learn something is to
jump right in, so lot's not waste any
time:

     To put an object on the board, press
F2 O.  After picking a character to
represent the object, you can enter a
program to control it.

NOTE: The following examples use a great
deal of comments (everything between a '
character and the end of a line is a
comment). ZZT will not recognize most of
these as comments and thus they should be
removed before using the code.

:simple;A Simple Example Program

 Commands    Comments
 ----------  -----------------
 @BadGuy
             ' We are giving this object
             ' the name "BadGuy".
 /s/s/s      ' Start out by moving south
             ' three times.
 #shoot n    ' Next, shoot north.
 #end        ' Now stop and wait for us to
             ' receive a message.
 :shot       ' When we receive a "SHOT"
             ' message, start doing the
             ' following commands.
 #shoot seek ' Shoot towards the player.
 #end        ' Stop and wait for another
             ' message.
 :touch      ' Do the following when we
             ' receive a "TOUCH" message
 Ouch! Stop touching me.
             ' Put the preceding text on
             ' the screen.
 #send shot  ' Next, send ourselves the
             ' message "SHOT".

     As soon as the player enters the
board this object is on, the program will
begin running at the top. This object will
immediately move three spaces south and
fire a shot to the north. When the program
reaches the #end statement, the object
will stop doing anything until a message
is sent to it.

     ZZT will send BadGuy the message
"SHOT" whenever the player (or something
else) shoots the BadGuy. The object will
then shoot in the direction of the player
and end program execution (stop running)
until another message is sent.

     Likewise, when the player (and only
the player) touches BadGuy, the object
will receive the "TOUCH" message. This
causes BadGuy to display the text "Ouch!
Stop touching me." at the bottom of the
screen.  This time, however, instead of
ending the program, the object sends
itself the message "SHOT" which causes it
to shoot in the direction of the player.

:end;The Importance of #end

     An object will continue executing its
code until it reaches either the end of
the program or an #end statement (as well
as in a few other situations to be
mentioned later).

$An example:

 @BadCode    ' Name of the object
 :touch      ' TOUCH label
 Humph. Don't touch me.

     In this program, the text "Humph.
Don't touch me." will be displayed
IMMEDIATELY.  Because there is no #end
statement, the program will continue
through the "TOUCH" label and begin
executing the code intended for the touch
message only. Do not fall into this trap!

:oop;Object Oriented Programming

     ZZT-OOP is a relatively simple
language and its commands are straight-
forward.  However, it becomes very
powerful as objects begin to interact with
each other.

     The primary difference between
ZZT-OOP and conventional languages such as
BASIC is the use of messages.

     The following two objects illustrate
a more intense use of messages:

$Here is the first object:

 @Lefty      ' This object's name.
 /e/e/e/e    ' Move east 4 times.
 /w/w/w/w    ' Then west 4 times.
 #send Righty:Do
             ' Send the "Do" message to
             ' the object named "Righty".
 #end        ' And halt. 

$Here is the other object:

 @Righty     ' This is our name.
 #end        ' Don't do anything until we
             ' receive a message.
 :do         ' Here's the "Do" message.
 /w/w/w/w    ' Move west 4 times.
 /e/e/e/e    ' Then east 4 times.
 #send lefty:restart
             ' Tell our counterpart to
             ' restart.
 #end        ' Done for now.

     These two objects form a feedback
loop.  When the game starts, Lefty will
move then send a message to Righty. This
causes Righty to move then tell Lefty to
restart.  So lefty moves, etc, etc, etc.

:flags;Using Flags

     Flags are a very useful way of
remembering information and communicating
between objects. Objects can only send
messages to each other if they are on the
same board.  Flags can be used across the
boards.

     Here are two objects which use flags.
These objects need not be on the same
board.

$Here is the first object:

 @Flask      ' Flask object.
 #end        ' Wait for message.
 :touch      ' Player touches the flask.
 You receive the magical elixir.
             ' Inform the player that they
             ' have received an elixir.
 #set elixir ' Set the flag "elixir"
 #die        ' Cease to exist

$Here is the second object:

 @Wizard     ' This object is a wizard.
 #end        ' Do nothing yet...
 :touch      ' The player wants to talk to
             ' the wizard.
 #if elixir thank
             ' If elixir has been set,
             ' send the message "THANK".
             ' Otherwise, continue.
 I only talk to people with magical
 elixirs. Go away.
 #end        ' Halt.
 :thank      ' Thank the player for the
             ' elixir.
 Thank you! I have been looking everywhere
 for my magical elixir. I'll take that
 from you now.
 #clear elixir
             ' Clear the flag "elixir".
 #end        ' Done.

     When the player touches the flask
object, it informs the player that he or
she has received a magical elixir and then
disappears (dies), which of course stops
program execution permanently.

     The wizard, when touched, will check
to see whether or not the elixir flag is
set.  If the flag is not set, the wizard
tells the player to find it for him. If it
is set, the message "THANK" is sent,
whereby the player is thanked and the
elixir is taken away.

     Up to ten flags may be set at one
time in a ZZT world.

:hyper;Hypertext Messages

In the above example, the Wizard rudely
takes the elixir from the player without
even asking whether or not the player
wishes to give it to him. This can,
fortunately, be remedied.

$A more polite Wizard

 @PoliteWizard
 #end
 :touch
 #if elixir thank
 If only you had a magical elixer...
 #end
             ' NEW code to follow:
 :thank      ' Thank the player for the
             ' elixir.
 Thank you! I have been looking everywhere
 for my magical elixir. May I please have
 it?
             ' Politely ask for the elixir
 
 !yes;Of course you can.
 !no;No! It is mine!
             ' Offer the player two
             ' choices.
 /i          ' Pause for input
 #send thank ' If a choice is not made,
             ' thank the player and ask
             ' again.
 :yes        ' The player decided to give
             ' up the elixir.
 Thank you very much. I am forever in your
 debt.
             ' Suck up to the player. :-)
 #clear elixir
 #end
 :no         ' The player decided to not
             ' give away the elixir.
 Very well then. See if I ever do anything
 nice for you.
 #end

Instead of simply taking the elixir away,
the PoliteWizard offers the player two
options, which will appear to the player
as such:

!;Of course you can.
!;No! It is mine!

The first option will send the message
"yes", while the second will send the
message "no". If neither option is
selected, the program continues. In this
case, the message "THANK" is sent again,
forcing the player to make a choice.

$Coming someday:

* Give and Take a Little
* Zapping Messages

$- - -

     Thus concludes this mini-tutorial.
Once you think you have a grasp of the
idea of ZZT-OOP programs and messages, you
are ready to proceed to... 

!-langref;The ZZT-OOP reference manual