[ibg.git] / chapters / 10.rst

====================
Captain Fate: take 1
====================

.. epigraph::

   | |CENTER| *S was a sailor, and spent all he got;*
   | |CENTER| *T was a tinker, and mended a pot.*

.. only:: html

  .. image:: /images/picS.png
     :align: left

|S|\imple though they are, our two games have covered most of the basic
functionality of Inform, providing enough solid ground underfoot for you to
start creating simple stories.  Even if some of what you've encountered
doesn't make sense yet, you should be able to browse a game's source code
and form a general understanding of what is going on.

We'll now design a third game, to show you a few additional features and
give you some more sample code to analyse.  In "Heidi" we tried to make
progress step by step, explaining every bit of code that went into the game
as we laid the objects sequentially; in "William Tell" you'll have noticed
that we took a few necessary explanatory detours, as the concepts grew more
interesting and complicated.  Here we'll organise the information in
logical didactic chunks, defining some of the objects minimally at first
and then adding complexity as need arises.  Again, this means that you
won't be able to compile for testing purposes after the addition of every
code snippet, so, if you're typing in the game as you read, you’ll need to
check the advice in :ref:`compile-as-you-go`.

A lot of what goes into this game we have already seen; you may deduce from
this that the game design business is fairly repetitious and that most
games are, when you reach the programming bottom line, another remake of
the same old theme.  Well, yes and no: you've got a camera and have seen
some short home videos in the making, but it’s a long way from here to
Casablanca.  To stick with the analogy, we'll now construct the opening
sequence of an indie B-movie, a tribute to the style of super-hero made
famous by a childhood of comic books:

.. pull-quote::

   "Impersonating mild mannered John Covarth, assistant help boy at an
   insignificant drugstore, you suddenly STOP when your acute hearing
   deciphers a stray radio call from the POLICE.  There’s some MADMAN
   attacking the population in Granary Park!  You must change into your
   Captain FATE costume fast...!"

which won't be so easy to do.  In this short example, players will win when
they manage to change into their super-hero costume and fly away to meet
the foe.  The confrontation will -- perhaps -- take place in some other
game, where we can but hope that Captain Fate will vanquish the forces of
evil, thanks to his mysterious (and here unspecified) superpowers.

Fade up on: a nondescript city street
=====================================

The game starts with meek John Covarth walking down the street.  We set up
the game as usual:

.. code-block:: inform

  !% -SD
  !============================================================================
  Constant Story "Captain Fate";
  Constant Headline
             "^A simple Inform example
              ^by Roger Firth and Sonja Kesserich.^";
  Release 3; Serial "040804";    ! for keeping track of public releases

  Constant MANUAL_PRONOUNS;
  Constant MAX_SCORE     2;
  Constant OBJECT_SCORE  1;
  Constant ROOM_SCORE    1;

  Include "Parser";
  Include "VerbLib";

  !============================================================================
  ! Object classes

  Class  Room
    with description "UNDER CONSTRUCTION",
    has  light;

  Class  Appliance
    with before [;
           Take,Pull,Push,PushDir:
             "Even though your SCULPTED adamantine muscles are up to the task,
              you don't favour property damage.";
         ],
    has  scenery;

  !============================================================================
  ! The game objects

  Room    street "On the street"
    with  name 'city' 'buildings' 'skyscrapers' 'shops' 'apartments' 'cars',
          description
              "On one side -- which your HEIGHTENED sense of direction
               indicates is NORTH -- there's an open cafe now serving
               lunch. To the south, you can see a phone booth.";

  !============================================================================
  ! The player's possessions

  !============================================================================
  ! Entry point routines

  [ Initialise;
      location = street;
      lookmode = 2;
      "^^Impersonating mild mannered John Covarth, assistant help boy at an
       insignificant drugstore, you suddenly STOP when your acute hearing
       deciphers a stray radio call from the POLICE. There's some MADMAN
       attacking the population in Granary Park! You must change into your
       Captain FATE costume fast...!^^";
  ];

  !============================================================================
  ! Standard and extended grammar

  Include "Grammar";
  !============================================================================

Almost everything is familar, apart from a few details:

.. code-block:: inform

  Constant MANUAL_PRONOUNS;
  Constant MAX_SCORE     2;
  Constant OBJECT_SCORE  1;
  Constant ROOM_SCORE    1;

By default, Inform uses a system of automatic pronouns: as the player
character moves into a room, the library assigns pronouns like IT and HIM
to likely objects (if you play "Heidi" or "William Tell" and type PRONOUNS,
you can see how the settings change).  There is another option.  If we
declare the ``MANUAL_PRONOUNS`` constant, we force the library to assign
pronouns to objects only as the player mentions them (that is, IT will be
unassigned until the player types, say, EXAMINE TREE, at which point, IT
becomes the TREE ).  The behaviour of pronoun assignment is a matter of
personal taste; no system is objectively perfect.

.. Generated by autoindex
.. index::
   pair: score; library variable
   pair: scored; library attribute

Apart from the constant ``MAX_SCORE`` that we have seen in "William Tell",
which defines the maximum number of points to be scored, we now see two
more constants: ``OBJECT_SCORE`` and ``ROOM_SCORE``.  There are several
scoring systems predefined in Inform.  In "William Tell" we've seen how you
can manually add (or subtract) points by changing the value of the variable
:var:`score`.  Another approach is to award points to players on the first
occasion that they (a) enter a particular room, or (b) pick up a particular
object.  To define that a room or object is indeed “particular”, all you
have to do is give it the attribute :attr:`scored`; the library take cares
of the rest.  The predefined scores are five points for finally reached
rooms and four points for wondrous acquisition of objects.  With the
constants ``OBJECT_SCORE`` and ``ROOM_SCORE`` we can change those defaults;
for the sake of example, we've decided to modestly award one point for
each.  By the way, the use of an equals sign ``=`` is optional with
``Constant``; these two lines have identical effect:

.. code-block:: inform

  Constant ROOM_SCORE    1;

  Constant ROOM_SCORE  = 1;

Another difference has to do with a special short-hand method that Inform
provides for displaying strings of text.  Until now, we have shown you:

.. code-block:: inform

  print "And now for something completely different...^"; return true;
  ...
  print_ret "And now for something completely different...";

Both lines do the same thing: they display the quoted string, output a
newline character, and return true.  As you have seen in the previous
example games, this happens quite a lot, so there is a yet shorter way of
achieving the same result:

.. code-block:: inform

  "And now for something completely different...";

That is, *in a routine* (where the compiler is expecting to find a
collection of statements each terminated by a semicolon), a string in
double quotes by itself, without the need for any explicit keywords, works
exactly as if there were a ``print_ret`` in front of it.  Remember that
this way of displaying text implies a ``return true`` at the end (which
therefore exits from the routine immediately).  This detail becomes
important if we *don't* want to return true after the string has been
displayed on the screen -- we should use the explicit ``print`` statement
instead.

.. Generated by autoindex
.. index::
   pair: name; library property

You'll notice that -- unusually for a room -- our ``street`` object has 
a :prop:`name` property:

.. code-block:: inform

  Room    street "On the street"
    with  name 'city' 'buildings' 'skyscrapers' 'shops' 'apartments' 'cars',
    ...

Rooms aren't normally referenced by name, so this may seem odd.  In fact,
we're illustrating a feature of Inform: the ability to define dictionary
words as "known but irrelevant" in this location.  If the player types
EXAMINE CITY here, the interpreter will reply "That's not something you
need to refer to in order to SAVE the day", rather than the misleading "You
can't see any such thing".  We mostly prefer to deal with such scenic words
using classes like ``Prop`` and ``Furniture``, but sometimes a room's
:prop:`name` property is a quick and convenient solution.

.. Generated by autoindex
.. index::
   pair: container; library attribute

In this game, we provide a class named ``Appliance`` to take care of
furniture and unmovable objects.  You’ll notice that the starting room we
have defined has no connections yet.  The description mentions a phone
booth and a café, so we might want to code those.  While the café will be a
normal room, it would seem logical that the phone booth is actually a big
box on the sidewalk; therefore we define a :attr:`container` set in the
street, which players may enter:

.. code-block:: inform

  Appliance booth "phone booth" street
    with name 'old' 'red' 'picturesque' 'phone' 'booth' 'cabin'
             'telephone' 'box',
         description
             "It's one of the old picturesque models, a red cabin with room
              for one caller.",
         before [;
           Open:
             "The booth is already open.";
           Close:
             "There's no way to close this booth.";
         ],
         after [;
           Enter:
             "With implausible celerity, you dive inside the phone booth.";
         ],
    has  enterable container open;

What's interesting are the attributes at the end of the definition.  You'll
recall from Heidi's ``nest`` object that a :attr:`container` is an object
capable of having other objects placed in it.  If we make something
:attr:`enterable`, players count as one of those objects, so that they may
squeeze inside.  Finally, ``containers`` are, by default, supposed to be
closed.  You can make them :attr:`openable` if you wish players to be able
to OPEN and CLOSE them at will, but this doesn't seem appropriate behaviour
for a public cabin -- it would become tedious to have to type OPEN BOOTH
and CLOSE BOOTH when these actions provide nothing special -- so we add
instead the attribute :attr:`open` (as we did with the nest), telling the
interpreter that the container is open from the word go.  Players aren't
aware of our design, of course; they may indeed try to OPEN and CLOSE the
booth, so we trap those actions in a :prop:`before` property which just
tells them that these are not relevant options.  The :prop:`after` property
gives a customised message to override the library’s default for commands
like ENTER BOOTH or GO INSIDE BOOTH.

Since in the street's description we have told players that the phone booth
is to the south, they might also try typing SOUTH.  We must intercept this
attempt and redirect it (while we're at it, we add a connection to the
as-yet-undefined café room and a default message for the movement which is
not allowed):

.. code-block:: inform

  Room    street "On the street"
    with  name city' 'buildings' 'skyscrapers' 'shops' 'apartments' 'cars',
          description
              "On one side -- which your HEIGHTENED sense of direction
               indicates is NORTH -- there's an open cafe now serving
               lunch. To the south, you can see a phone booth.",
          n_to cafe,
          s_to [; <<Enter booth>>; ],
          cant_go
              "No time now for exploring! You'll move much faster in your
               Captain FATE costume.";

That takes care of entering the booth.  But what about leaving it?  Players
may type EXIT or OUT while they are inside an enterable container and the
interpreter will oblige but, again, they might type NORTH.  This is a
problem, since we are actually in the street (albeit inside the booth) and
to the north we have the café.  We may provide for this condition in the
room's :prop:`before` property:

.. code-block:: inform

  before [;
    Go:
      if (player in booth && noun == n_obj) <<Exit booth>>;
  ],

Since we are outdoors and the booth provides a shelter, it's not impossible
that a player may try just IN, which is a perfectly valid connection.
However, that would be an ambiguous command, for it could also refer to the
café, so we express our bafflement and force the player to try something
else:

.. code-block:: inform

  n_to cafe,
  s_to [; <<Enter booth>>; ],
  in_to "But which way?",

Now everything seems to be fine, except for a tiny detail.  We've said
that, while in the booth, the player character’s location is still the
``street`` room, regardless of being inside a :attr:`container`; if players
chanced to type LOOK, they'd get:

.. code-block:: transcript

  On the street (in the phone booth)
  On one side -- which your HEIGHTENED sense of direction indicates is NORTH --
  there's an open cafe now serving lunch. To the south, you can see a 
  phone booth.

Hardly an adequate description while *inside* the booth.  There are several
ways to fix the problem, depending on the result you wish to achieve.  The
library provides a property called :prop:`inside_description` which you can
utilise with enterable containers.  It works pretty much like the normal
:prop:`description` property, but it gets printed only when the player is
inside the container.  The library makes use of this property in a very
clever way, because for every LOOK action it checks whether we can see
outside the container: if the container has the :attr:`transparent`
attribute set, or if it happens to be :attr:`open`, the library displays
the normal :prop:`description` of the room first and then the
:prop:`inside_description` of the container.  If the library decides we
can’t see outside the container, only the :prop:`inside_description` is
displayed.  Take for instance the following (simplified) example:

.. code-block:: inform

  Room    stage "On stage"
    with  description
              "The stage is filled with David Copperfield's
               magical contraptions.",
          ...

  Object  magic_box "magic box" stage
    with  description
              "A big elongated box decorated with silver stars, where
               scantily clad ladies make a disappearing act.",
          inside_description
              "The inside panels of the magic box are covered with black
               velvet. There is a tiny switch by your right foot.",
          ...
    has   container openable enterable light;

Now, the player would be able to OPEN BOX and ENTER BOX.  A player who
tried a LOOK would get:

.. code-block:: transcript

  On stage (in the magic box)
  The stage is filled with David Copperfield's magical contraptions.

  The inside panels of the magic box are covered with black velvet. There is a
  tiny switch by your right foot.

If now the player closes the box and LOOKs:

.. code-block:: transcript

  On stage (in the magic box)
  The inside panels of the magic box are covered with black velvet. There is a
  tiny switch by your right foot.

In our case, however, we don't wish the description of the street to be
displayed at all (even if a caller is supposedly able to see the street
while inside a booth).  The problem is that we have made the booth an
:attr:`open` container, so the street's description would be displayed
every time.  There is another solution.  We can make the
:prop:`description` property of the ``street`` room a bit more complex, and
change its value: instead of a string, we write an embedded routine.
Here's the (almost) finished room:

.. code-block:: inform

  Room    street "On the street"
    with  name 'city' 'buildings' 'skyscrapers' 'shops' 'apartments' 'cars',
          description [;
              if (player in booth)
                  "From this VANTAGE point, you are rewarded with a broad view
                   of the sidewalk and the entrance to Benny's cafe.";
              else
                  "On one side -- which your HEIGHTENED sense of direction
                   indicates is NORTH -- there's an open cafe now serving
                   lunch. To the south, you can see a phone booth.";
          ],
          before [;
            Go:
              if (player in booth && noun == n_obj) <<Exit booth>>;
          ],
          n_to cafe,
          s_to [; <<Enter booth>>; ],
          in_to "But which way?",
          cant_go
               "No time now for exploring! You'll move much faster in your
                Captain FATE costume.";

The description while inside the booth mentions the sidewalk, which 
might invite the player to EXAMINE it.  No problem:

.. code-block:: inform

  Appliance "sidewalk" street
    with  name sidewalk' 'pavement' 'street',
          article "the",
          description
              "You make a quick surveillance of the sidewalk and discover much
               to your surprise that it looks JUST like any other sidewalk in
               the CITY!";

Unfortunately, both descriptions also mention the café, which will be a 
room and therefore not, from the outside, an examinable object.  The 
player may enter it and will get whatever description we code as the 
result of a LOOK action (which will have to do with the way the café 
looks from the *inside*); but while we are on the street we need 
something else to describe it:

.. code-block:: inform

  Appliance outside_of_cafe "Benny's cafe" street
    with  name 'benny^s' 'cafe' 'entrance',
          description
              "The town's favourite for a quick snack, Benny's cafe has a 50's
               ROCKETSHIP look.",
          before [;
            Enter:
              print "With an impressive mixture of hurry and nonchalance
                  you step into the open cafe.^";
              PlayerTo(cafe);
              return true;
          ],
    has   enterable proper;

.. index:: accented characters

.. note::

   Although the text of our guide calls Benny's establishment a "café" --
   note the acute "e" -- the game itself simplifies this to "cafe".  We do
   this for clarity, not because Inform doesn't support accented
   characters.  The |DM4| explains in detail how to display these
   characters in :dm4:`§1.11 <s1.html#s1_11>` "*How text is printed*" and
   provides the whole Z-machine character set in Table 2.  In our case, we
   could have displayed this::

      The town's favourite for a quick snack, Benny's café has a 50's ROCKETSHIP look.

   by defining the :prop:`description` property as any of these:

   .. code-block:: inform

      description
          "The town's favourite for a quick snack, Benny's caf@'e has a 50's
           ROCKETSHIP look.",

      description
          "The town's favourite for a quick snack, Benny's caf@@170 has a 50's
           ROCKETSHIP look.",

      description
          "The town's favourite for a quick snack, Benny's caf@{E9} has a 50's
           ROCKETSHIP look.",

   However, all three forms are harder to read than the vanilla "cafe", so
   we've opted for the simple life.

Unlike the sidewalk object, we offer more than a mere description.  Since
the player may try ENTER CAFE as a reasonable way of access -- which would
have confused the interpreter immensely -- we take the opportunity of
making this object also :attr:`enterable`, and we cheat a little.  The
attribute :attr:`enterable` has permitted the verb ENTER to be applied to
this object, but this is not a :attr:`container`; we want the player to be
sent into the *real* café room instead.  The :prop:`before` property handles
this, intercepting the action, displaying a message and teleporting the
player into the café.  We ``return true`` to inform the interpreter that we
have taken care of the :act:`Enter` action ourselves, so it can stop right
there.

.. Generated by autoindex
.. index::
   pair: n_to; library property

As a final detail, note that we now have two ways of going into the café:
the :prop:`n_to` property of the ``street`` room and the :act:`Enter`
action of the ``outside_of_cafe`` object.  A perfectionist might point out
that it would be neater to handle the actual movement of the player in just
one place of our code, because this helps clarity.  To achieve this, we
redirect the street's :prop:`n_to` property thus:

.. code-block:: inform

  n_to [; <<Enter outside_of_cafe>>; ],

You may think that this is unnecessary madness, but a word to the wise: in
a large game, you want action handling going on just in one place when
possible, because it will help you to keep track of where things are
a-happening if something goes *ploof* (as, believe us, it will; see
:doc:`16`).  You don't need to be a perfectionist, just cautious.

A booth in this kind of situation is an open invitation for the player to
step inside and try to change into Captain Fate's costume.  We won't let
this happen -- the player isn't Clark Kent, after all; later we'll explain
how we forbid this action -- and that will force the player to go inside
the café, looking for a discreet place to disrobe; but first, let's freeze
John Covarth outside Benny's and reflect about a fundamental truth.

A hero is not an ordinary person
================================

Which is to say, normal actions won't be the same for him.

.. Generated by autoindex
.. index::
   pair: Sing; library action

As you have probably inferred from the previous chapters, some of the
library’s standard defined actions are less important than others in making
the game advance towards one of its conclusions.  The library defines PRAY
and SING, for instance, which are of little consequence in a normal gaming
situation; each displays an all-purpose message, sufficiently
non-committal, and that's it.  Of course, if your game includes a magic
portal that will reveal itself only if the player lets rip with a snatch of
Wagner, you may intercept the :act:`Sing` action in a :prop:`before`
property and alter its default, pretty useless behaviour.  If not, it's
"Your singing is abominable" for you.

All actions, useful or not, have a stock of messages associated with them
(the messages are held in the ``english.h`` library file and listed in
:dm4:`Appendix 4 <sa4.html>` of the |DM4|).  We have already seen one way
of altering the player character's description -- "As good looking as ever"
-- in "William Tell", but the other defaults may also be redefined to suit
your tastes and circumstantial needs.

.. index::
   pair: LibraryMessages; library object

John Covarth, aka Captain Fate, could happily settle for most of these
default messages, but we deem it worthwhile to give him some customised
responses.  If nothing else, this adds to the general atmosphere, a nicety
that many players regard as important.  For this mission, we make use of
the :obj:`LibraryMessages` object.

.. code-block:: inform

  Include "Parser";

  Object  LibraryMessages         ! must be defined between Parser and VerbLib
    with  before [;
            Buy:    "Petty commerce interests you only on COUNTED occasions.";
            Dig:    "Your keen senses detect NOTHING underground worth your
                     immediate attention.";
            Pray:   "You won't need to bother almighty DIVINITIES to save
                     the day.";
            Sing:   "Alas! That is not one of your many superpowers.";
            Sleep:  "A hero is ALWAYS on the watch.";
            Strong: "An unlikely vocabulary for a HERO like you.";
            Swim:   "You quickly turn all your ATTENTION towards locating a
                     suitable place to EXERCISE your superior strokes,
                     but alas! you find none.";
            Miscellany:
              if (lm_n == 19)
                  if (clothes has worn)
                      "In your secret identity's outfit, you manage most
                       efficaciously to look like a two-cent loser, a
                       good-for-nothing wimp.";
                  else
                      "Now that you are wearing your costume, you project
                       the image of power UNBOUND, of ballooned,
                       multicoloured MUSCLE, of DASHING yet MODEST chic.";
              if (lm_n == 38)
                  "That's not a verb you need to SUCCESSFULLY save the day.";
              if (lm_n == 39)
                  "That's not something you need to refer to in order to
                   SAVE the day.";
        ];

  Include "VerbLib";

If you provide it, the :obj:`LibraryMessages` object must be defined
*between* the inclusion of ``Parser`` and ``VerbLib`` (it won't work
otherwise and you’ll get a compiler error).  The object contains a single
property -- :prop:`before` -- which intercepts display of the default
messages that you want to change.  An attempt to SING, for example, will
now result in "Alas!  That is not one of your many superpowers" being
displayed.

In addition to such verb-specific responses, the library defines other
messages not directly associated with an action, like the default response
when a verb is unrecognised, or if you refer to an object which is not in
scope, or indeed many other things.  Most of these messages can be accessed
through the ``Miscellany entry``, which has a numbered list of responses.
The variable ``lm_n`` holds the current value of the number of the message
to be displayed, so you can change the default with a test like this:

.. code-block:: inform

  if (lm_n == 39)
      "That's not something you need to refer to in order to SAVE the day.";

where 39 is the number for the standard message "That's not something you
need to refer to in the course of this game" -- displayed when the player
mentions a noun which is listed in a room's name property, as we did for
the ``street``.

.. note::

   Remember that when we are testing for different values of the same
   variable, we can also use the switch statement.  For the Miscellany
   entry, the following code would work just as nicely:

   .. code-block:: inform

     ...
     Miscellany:
       switch (lm_n) {
         19:
           if (clothes has worn)
               "In your secret identity's outfit, you manage most
                efficaciously to look like a two-cent loser, a
                good-for-nothing wimp.";
           else
               "Now that you are wearing your costume, you project
                the image of power UNBOUND, of ballooned,
                multicoloured MUSCLE, of DASHING yet MODEST chic.";
         38:
           "That's not a verb you need to SUCCESSFULLY save the day.";
         39:
           "That's not something you need to refer to in order to SAVE the day.";
       }

.. index::
   pair: LibraryMessages; library object

.. Generated by autoindex
.. index::
   pair: Miscellany; library action

Not surprisingly, the default message for self-examination: "As good
looking as ever" is a :act:`Miscellany` entry -- it's number 19 -- so we
can change it through the :obj:`LibraryMessages` object instead of, as
before, assigning a new string to the ``player.description`` property.  In
our game, the description of the player character has two states: with
street clothes as John Covarth and with the super-hero outfit as Captain
Fate; hence the ``if (clothes has worn)`` clause.

This discussion of changing our hero's appearance shows that there are
different ways of achieving the same result, which is a common situation
while designing a game.  Problems may be approached from different angles;
why use one technique and not another?  Usually, the context tips the
balance in favour of one solution, though it might happen that you opt for
the not-so-hot approach for some overriding reason.  Don't feel
discouraged; choices like this become more common (and easier) as your
experience grows.

.. Ugh.  Ghastly, but it does the job.

.. |WNL_LATEX| replace:: :latex:`\emph{\textbf{whatever new look}}`

.. |WNL_HTML|  replace:: :html:`<strong><em>whatever new look</em></strong>`

.. note::

   Going back to our example, an alternative approach would be to set the
   variable ``player.description`` in the ``Initialise`` routine (as we did
   with "William Tell") to the "ordinary clothes" string, and then later
   change it as the need arises.  It is a variable, after all, and you can
   alter its value with another statement like ``player.description =``
   |WNL_LATEX| |WNL_HTML| anywhere in your code.  This alternative solution
   might be better if we intended changing the description of the player
   many times through the game.  Since we plan to have only two states, the
   :obj:`LibraryMessages` approach will do just fine.

A final warning: as we explained when extending the standard verb grammars,
you *could* edit the appropriate library file and change all the default
messages, but that wouldn't be a sound practice, because your library file
will probably not be right for the next game.  Use of the
:obj:`LibraryMessages` object is strongly advised.

If you're typing in the game, you'll probably want to read the brief
section on :ref:`compile-as-you-go` prior to performing a test compile.
Once everything's correct, it’s time that our hero entered that enticing
café.