Revert to original minimal Inform lexer.

[ibg.git] / chapters / 12.rst

====================
Captain Fate: take 3
====================

.. epigraph::

   | *W was a watchman, and guarded the door;*
   | *X was expensive, and so became poor.*

.. only:: html

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

.. raw:: latex

   \dropcap{w}

e've given ourselves an interesting challenge by overusing that 
convenient word "toilet", and here we show you how we resolve the 
ambiguities that have been introduced. Also, it's time for the eponymous 
owner of Benny's café to be developed in full.

Too many toilets
================

If you check the ``name`` properties of the toilet door, the toilet key 
and the toilet room, you’ll see that the dictionary word ``'toilet'`` 
occurs in all of them. There won't be any problems if players mention 
the words DOOR or KEY, but we reach a strange impasse should they try to 
perform some action with just the word TOILET. The interpreter has to 
think fast: is the player talking about the key? About the door? Or 
about the toilet? Unable to decide, it asks: "Which do you mean, the 
door to the toilet, the toilet key or the toilet?"

And guess what? Players will never be able to refer to the toilet object 
(unless they type BATH ROOM or REST ROOM, not an obvious choice since we 
haven't used those phrases anywhere visible). If the player answers 
TOILET the parser will still have three objects with that dictionary 
word as a possible name, so it will ask again, and again -- until we 
give it some dictionary word which is not ambiguous. A human reader 
would be able to understand that the word TOILET alone refers to the 
room, but the interpreter won't -- unless we help it a little.

We could work around this problem in more than one way, but we'll take 
this opportunity of demonstrating the use of a third-party library 
package.

When experienced designers find a problem which is not easily solvable, 
they may come up with a smart solution and then consider that others 
could benefit from the effort. The product of this generosity takes the 
form of a library extension: the solution neatly packaged as a file that 
other designers can incorporate into their source code. These files can 
be found in the IF Archive: go to 
``http://mirror.ifarchive.org/indexes/if-archive.html`` and then select 
"``.../infocom``", "``.../compilers``", "``.../inform6``", 
"``.../library``", and "``.../contributions``". All of these files 
contain Inform code. To use a library extension (also known as a library 
contribution), you should download it and read the instructions (usually 
embedded as comments in the file, but occasionally supplied separately) 
to discover what to do next. Normally, you ``Include`` it (as we have 
already done with ``Parser``, ``VerbLib`` and ``Grammar``), but often 
there are rules about where exactly this Include should be placed in 
your source code. It is not unusual to find other suggestions and 
warnings.

To help us out of the disambiguation problem with the word TOILET, we 
are going to use Neil Cerutti's extension ``pname.h``, which is designed 
for situations precisely like this. First, we follow the link to the IF 
archive and download the compressed file ``pname.zip``, which contains 
two more files: ``pname.h`` and ``pname.txt``. We place these files in 
the folder where we are currently developing our game or, if using the 
environment we proposed in "Tools of the trade" on page 17, in the 
``Inform\Lib\Contrib`` folder. The text file offers instructions about 
installation and usage. Here we find a warning:

  This version of pname.h is recommended for use only with version 6/10 
  of the Inform Library.

We're actually using a later version, but this doesn't seem to cause a 
problem. Most extensions aren't so fussy, but ``pname.h`` fiddles with 
some routines at the heart of the standard library; these may not be 
identical in other Inform versions.

The introduction explains what ``pname.h`` does for you; namely, it lets 
you avoid using complicated ``parse_name`` routines to disambiguate the 
player's input when the same dictionary word refers to more than one 
item. A ``parse_name`` routine would have been the solution to our 
problem before the existence of this file, and it qualifies as an 
advanced programming topic, difficult to master on a first approach. 
Fortunately, we don't need to worry. Neil Cerutti explains:

  The ``pname.h`` package defines a new object property, ``pname`` 
  (short for phrase name), with a similar look and feel to the standard 
  ``name`` property: both contain a list of dictionary words. However, 
  in a ``pname`` property the order of the words is significant, and 
  special operators ``'.p'`` ``'.or'`` and ``'.x'`` enable you to embed 
  some intelligence into the list. In most cases where the standard 
  ``name`` property isn't enough, you can now just replace it with a 
  ``pname`` property, rather than write a ``parse_name`` property 
  routine.

We'll soon see how it works. Let's take a look at the installation 
instructions:

  To incorporate this package into your program, do three things:

  #.  Add four lines near the head of the program (before you include 
      ``Parser.h``).

      ``Replace MakeMatch;``
      ``Replace Identical;``
      ``Replace NounDomain;``
      ``Replace TryGivenObject;``

  #.  Include the ``pname.h`` header just after you include ``Parser.h``.
      ``Include "Parser";``
      ``Include "pname";``

  #.  Add ``pname`` properties to those objects which require phrase 
      recognition.

It seems simple enough. So, following steps one and two, we add those 
``Replace...`` lines before the inclusion of ``Parser``, and we include 
``pname.h`` right after it. ``Replace`` tells the compiler that we're 
providing replacements for some standard routines.

.. code-block:: inform

  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;

  Replace MakeMatch;              ! requited by pname.h
  Replace Identical;
  Replace NounDomain;
  Replace TryGivenObject;

  Include "Parser";
  Include "pname";
  !...

Now our source code is ready to benefit from the library package. How 
does it work? We have acquired a new property -- ``pname`` -- which can 
be added to some of our objects, and which works pretty much like a 
``name`` property. In fact, it should be used *instead* of a ``name`` 
property where we have a disambiguation problem. Let’s change the 
relevant lines for the toilet door and the toilet key:

.. todo::

  Maybe specially highlight the lines using pname?

.. code-block:: inform

  Object  toilet_door
    with  pname '.x' 'red' '.x' 'toilet' 'door',
          short_name [;
          !...

  Object  toilet_key "toilet key" benny
    with  pname '.x' 'toilet' 'key',
          article "the",
          !...

while leaving the ``outside_of_toilet`` unchanged:

.. code-block:: inform

  Object  outside_of_toilet "toilet" cafe
    with  name 'toilet' 'bath' 'rest' 'room' 'bathroom' 'restroom',
          before [;
          !...

We are now using a new operator -- ``'.x'`` -- in our ``pname`` word 
lists. explains

  The first dictionary word to the right of a ``'.x'`` operator is 
  interpreted as optional.

and this makes the dictionary word ``'toilet'`` of lesser importance for 
these objects, so that at run-time players could refer to the DOOR or 
TOILET DOOR or the KEY or TOILET KEY -- but not simply to the TOILET -- 
when referring to either the door or the key. And, by leaving unchanged 
the name property of the outside_of_toilet object – where there is also 
another ``'toilet'`` entry -- the ``pname`` properties will tell the 
interpreter to discard the key and the door as possible objects to be 
considered when players refer just to TOILET. Looking at it in terms of 
the English language, we've effectively said that "TOILET" is an 
adjective in the phrases "TOILET DOOR" and "TOILET KEY", but a noun when 
used on its own to refer to the room.

The ``pname.h`` package has additional functionality to deal with more 
complex phrases, but we don't need it in our example game. Feel free, 
however, to read ``pname.txt`` and discover what this fine library 
extension can do for you: it's an easy answer to many a disambiguation 
headache.


Don't shoot! I'm only the barman
================================

A lot of the action of the game happens around Benny, and his definition 
needs a little care. Let's explain what we want to happen.

  So the door is locked and the player, after discovering what the note 
  stuck on the toilet door said, will eventually ask Benny for the key. 
  Sadly, Benny allows use of the toilet only to customers, a remark 
  he'll make looking pointedly at the menu board behind him. The player 
  will have to ask for a coffee first, thereby qualifying as a customer 
  in Benny's eyes and thus entitled to make use of the toilet. At last! 
  Rush inside, change into Captain Fate’s costume and fly away to save 
  the day!

Except that the player neither paid for the coffee, nor returned the 
toilet key. Benny will have to stop the player from leaving the café in 
these circumstances. To prevent unnecessary complication, there will be 
a coin near the lavatory, enough cash to pay for the coffee. And that 
about sums it all up; pretty simple to describe -- not so simple to 
code. Remember Benny's basic definition from the previous chapter:

.. code-block:: inform

  Object  benny "Benny" cafe
    with  name 'benny',
          description
              "A deceptively FAT man of uncanny agility, Benny entertains his
               customers crushing coconuts against his forehead when the mood
               strikes him.",
    has   scenery animate male proper transparent;

We can now add some complexity, beginning with a ``life`` property. In 
generic form:

.. code-block:: inform

  life [;
    Give:             !... code for giving objects to Benny
    Attack:           !... code to deal with player's aggressive moves
    Kiss:             !... code about the player getting tender on Benny
    Ask,Tell,Answer:  !... code to handle conversation
  ],

We have seen some of these actions before. We'll take care of the easier 
ones:

.. code-block:: inform

  Attack:
    if (costume has worn) {
        deadflag = 4;
        print "Before the horror-stricken eyes of the surrounding
               people, you MAGNIFICENTLY jump OVER the counter and
               attack Benny with REMARKABLE, albeit NOT sufficient,
               speed. Benny receives you with a TREACHEROUS upper-cut
               that sends your GRANITE JAW flying through the cafe.^^
               ~These guys in pyjamas think they can bully innocent
               folk,~ snorts Benny, as the EERIE hands of DARKNESS
               engulf your vision and you lose consciousness.";
    }
    else
        "That would be an unlikely act for MEEK John Covarth.";

    Kiss:
      "This is no time for MINDLESS infatuation.";

    Ask,Tell,Answer:
      "Benny is too busy for idle chit-chat.";

Attacking Benny is not wise. If the player is still dressed as John 
Covarth, the game displays a message refusing to use violence by reason 
of staying in character as a worthless wimp. However, if Captain Fate 
attempts the action, we'll find that there is more to Benny than meets 
the eye, and the game is lost. Kissing and conversation are disallowed 
by a couple of tailored responses.

The Give action is a bit more complicated, since Benny reacts to certain 
objects in a special and significant way. Bear in mind that Benny's 
definition needs to keep track of whether the player has asked for a 
coffee (thereby becoming a customer and thus worthy of the key), whether 
the coffee has been paid for, and whether the toilet key has been 
returned. The solution, yet again (this really is a most useful 
capability), is more local property variables:

.. code-block:: inform

  Object  benny "Benny" cafe
    with  name 'benny',
          description
              "A deceptively FAT man of uncanny agility, Benny entertains his
               customers crushing coconuts against his forehead when the mood
               strikes him.",
          coffee_asked_for false,          ! has player asked for a coffee?
          coffee_not_paid  false,          ! is Benny waiting to be paid?
          key_not_returned false,          ! is Benny waiting for the key?
          live [;
          !...

Now we are ready to tackle the ``Give`` action of the ``life`` property, 
which deals with commands like GIVE THE KEY TO BENNY (in a moment, we'll 
come to the ``Give`` action of the ``orders`` property, which deals with 
commands like BENNY, GIVE ME THE KEY):

.. code-block:: inform

  Give:
    switch (noun) {
      clothes:
        "You NEED your unpretentious John Covarth clothes.";
      costume:
        "You NEED your stupendous ACID-PROTECTIVE suit.";
      toilet_key:
        self.key_not_returned = false;
        move toilet_key to benny;
        "Benny nods as you ADMIRABLY return his key.";
      coin:
        remove coin;
        self.coffee_not_paid = false;
        print "With marvellous ILLUSIONIST gestures, you produce the
               coin from the depths of your ";
        if (costume has worn) print "BULLET-PROOF costume";
        else                  print "ordinary street clothes";
        " as if it had dropped on the counter from Benny's ear!
         People around you clap politely. Benny takes the coin
         and gives it a SUSPICIOUS bite. ~Thank you, sir. Come
         back anytime,~ he says.";
    }

The Give action in the ``life`` property holds the variable ``noun`` as 
the object offered to the NPC. Remember that we can use the ``switch`` 
statement as shorthand for:

.. code-block:: inform

  if (noun == costume) { whatever };
  if (noun == clothes) { whatever };
  !...

We won't let players give away their clothes or their costume (yes, an 
improbable action, but you never know). The toilet key and the coin are 
successfully transferred. The property ``key_not_returned`` will be set 
to true when we receive the toilet key from Benny (we have not coded 
that bit yet), and now, when we give it back, it's reset to ``false``. 
The ``move`` statement is in charge of the actual transfer of the object 
from the player's inventory to Benny, and we finally display a 
confirmation message. With the coin, we find a new statement: 
``remove``. This extracts the object from the object tree, so that it 
now has no parent. The effect is to make it disappear from the game 
(though you are not destroying the object permanently -- and indeed you 
could return it to the object tree using the ``move`` statement); as far 
as the player is concerned, there isn’t a COIN to be found anywhere. The 
``coffee_not_paid`` property will be set to true when Benny serves us 
the cup of coffee (again, we’ll see that in a moment); now we reset it 
to ``false``, which liberates the player from debt. This culminates with 
the ``"..."`` print-and-return statement, telling the player that the 
action was successful. In passing, remember that in "A homely 
atmosphere" on page 131 we defined the counter such that PUT KEY ON 
COUNTER is automatically translated into GIVE KEY TO BENNY .

Why move the key to Benny but remove the coin instead? Once players 
qualify as customers by ordering a coffee, they will be able to ask for 
the key and return it as many times as they like, so it seems sensible 
to keep the key around. The coin, however, will be a one-shot. We won't 
let players ask for more than one coffee, to prevent their debt from 
growing ad infinitum -- besides, they came in here to change, not to 
indulge in caffeine. Once the coin is paid, it disappears for good, 
supposedly into Benny's greedy pockets. No need to worry about it any 
more.

The benny object needs also an ``orders`` property, just to take care of 
the player's requests for coffee and the key, and to fend off any other 
demands. The ``Give`` action in an ``orders`` property deals with inputs 
like ASK BENNY FOR THE KEY or BENNY, GIVE ME THE KEY. The syntax is 
similar to that of the ``life`` property:

.. code-block:: inform

  orders [;   ! handles ASK BENNY FOR X and BENNY, GIVE ME XXX
    Give:
      if (second ~= player or nothing) "Benny looks at you strangely.";
      switch (noun) {
        toilet_key:
          if (toilet_key in player) "But you DO have the key already.";
          if (self.coffee_asked_for == true)
              if (toilet_key in self) {
                  move toilet_key to player;
                  self.key_not_returned = true;
                  "Benny tosses the key to the rest rooms on the
                   counter, where you grab it with a dextrous and
                   precise movement of your HYPER-AGILE hand.";
              }
              else
                  "~Last place I saw that key, it was in YOUR
                   possession,~ grumbles Benny. ~Be sure to return it
                   before you leave.~";
          else
              "~Toilet is only fer customers,~ he grumbles, looking
               pointedly at a menu board behind him.";
        coffee:
          if (self.coffee_asked_for == true)
              "One coffee should be enough.";
          move coffee to counter;
          self.coffee_asked_for = self.coffee_not_paid = true;
          "With two gracious steps, Benny places his world-famous
           Cappuccino in front of you.";
        food:         
          "Food will take too much time, and you must change NOW.";
        menu:
          "With only the smallest sigh, Benny nods towards the menu
           on the wall behind him.";
        default:
          "~I don't think that's on the menu, sir.~";
      }
  ],

* We test the value of ``second`` in order to trap over-generous 
  gestures such as BENNY, GIVE COFFEE TO CUSTOMERS . Then we consider 
  potential requests.

* **Toilet key:** first, we check whether players already have the key 
  or not, and complain if they do, stopping execution thanks to the 
  implicit ``return true`` of the ``"..."`` statement. If players don’t 
  have the  key, we proceed to check whether they've asked for a coffee 
  yet, by testing the ``coffee_asked_for`` property. If this is true , 
  we should also check if the key is actually one of Benny’s 
  possessions -- a perverse player could get the key, then drop it 
  somewhere and ask for it again; if this should happen, we indicate 
  that Benny is nobody's fool with the message ``"~Last place I saw 
  that key..."``. Once all these fitting conditions are ``true``, 
  players will get the key, which means that they have to return it -- 
  the ``key_not_returned`` property becomes ``true`` -- and we display 
  a suitable message. However, if the player didn't ask for a coffee, 
  Benny refuses to oblige, mentioning for the first time the menu board 
  where players will be able to see a picture of a cup of coffee when 
  they EXAMINE it. Take care to see how all the ``else`` clauses pair 
  up with the appropriate if statements, triggering responses for each 
  of the conditions that wasn't met.

* **Coffee:** we check whether players have already asked for a coffee, 
  by testing the ``coffee_asked_for`` property, and refuse to serve 
  another one if ``true``. If ``false``, we place the coffee on the 
  counter, and set the properties ``coffee_asked_for`` and 
  ``coffee_not_paid`` to ``true``. The message bit you know about.

* **Food:** we'll provide an object to deal with all of the delicious 
  comestibles to be found in the café, specifically those (such as 
  "pastries and sandwiches") mentioned in our descriptions. Although 
  that object is not yet defined, we code ahead to thwart player's 
  gluttony in case they choose to ask Benny for food.

* **Menu:** our default response -- "I don’t think that’s on the menu, 
  sir" -- isn’t very appropriate if the player asks for a menu, so we 
  provide a better one.

* **Default:** this takes care of anything else that the player asks 
  Benny for, displaying his curt response.

And before you know it, Benny's object is out of the way; however, don't
celebrate too soon. There’s still some Benny-related behaviour that, 
curiously enough, doesn’t happen in Benny's object; we're talking about 
Benny's reaction if the player tries to leave without paying or 
returning the key. We promised you that Benny would stop the player, and 
indeed he will. But where?

We must revisit the café room object:

.. code-block:: inform

  Room     cafe "Inside Benny's cafe"
    with   description
               "Benny's offers the FINEST selection of pastries and sandwiches.
                Customers clog the counter, where Benny himself manages to
                serve, cook and charge without missing a step. At the north side
                of the cafe you can see a red door connecting with the toilet.",
           before [;
             Go:   ! The player is about to depart. Is he making for the street?
               if (noun ~= s_obj) return false;
               if (benny.coffee_not_paid == true ||
                   benny.key_not_returned == true) {
                   print "Just as you are stepping into the street, the big hand
                          of Benny falls on your shoulder.";
                   if (benny.coffee_not_paid == true &&
                       benny.key_not_returned == true)
                       "^^~Hey! You've got my key and haven't paid for the
                        coffee. Do I look like a chump?~ You apologise as only a
                        HERO knows how to do and return inside.";
                   if (benny.coffee_not_paid == true)
                       "^^~Just waidda minute here, Mister,~ he says.
                        ~Sneaking out without paying, are you?~ You quickly 
                        mumble an excuse and go back into the cafe. Benny
                        returns to his chores with a mistrusting eye.";
                   if (benny.key_not_returned == true)
                       "^^~Just where you think you're going with the toilet
                        key?~ he says. ~You a thief?~ As Benny forces you back
                        into the cafe, you quickly assure him that it was only
                        a STUPEFYING mistake.";
               }     
               if (costume has worn) {
                   deadflag = 5;           ! you win!
                   "You step onto the sidewalk, where the passing pedestrians
                    recognise the rainbow EXTRAVAGANZA of Captain FATE's costume
                    and cry your name in awe as you JUMP with sensational
                    momentum into the BLUE morning skies!";
               }
           ],
           first_time_out false,           ! Captain Fate's first appearance?
           after [;
             Go:   ! The player has just arrived. Did he come from the toilet?
               if (noun ~= s_obj) return false;
               if (costume has worn && self.first_time_out == false) {
                   self.first_time_out = true;
                   StartDaemon(customers);
               }
           ],
           s_to  street,
           n_to  toilet_door;

Once again, we find that the solution to a design problem is not 
necessarily unique. Remember what we saw when dealing with the player's 
description: we could have assigned a new value to the 
``player.description`` variable, but opted to use the 
``LibraryMessages`` object instead. This is a similar case. The code 
causing Benny to intercept the forgetful player could have been added, 
perhaps, to a ``daemon`` property in Benny’s definition. However, since 
the action to be intercepted is always the same one and happens to be a 
movement action when the player tries to leave the café room, it is also 
possible to code it by trapping the ``Go`` action of the room object. 
Both would have been right, but this is somewhat simpler.

We have added a ``before`` property to the room object (albeit a longish 
one), just dealing with the ``Go`` action. As we mentioned in an earlier 
chapter, this technique lets you trap the player who is about to exit a 
room before the movement actually takes place, a good moment to 
interfere if we want to prevent escape. The first line:

.. code-block:: inform

  if (noun ~= s_obj) return false;

is telling the interpreter that we want to tamper only with southwards 
movement, allowing the interpreter to apply normal rules for the other 
available directions.

From here on, it's only conditions and more conditions. The player may 
attempt to leave:

* without paying for the coffee and without returning the key,

* having paid for the coffee, but without returning the key,

* having returned the key, but not paid for the coffee, or

* free of sin and accountable for nothing in the eyes of all men (well, 
  in the eye of Benny, at least).

The first three are covered by the test:

.. code-block:: inform

  if (benny.coffee_not_paid == true || benny.key_not_returned == true) ...

that is, if either the coffee is not paid for *or* if the key is not 
returned. When this condition is ``false``, it means that both 
misdemeanours have been avoided and that the player is free to go. 
However, when this condition is ``true``, the hand of Benny falls on the 
player's shoulder and then the game displays a different message 
according to which fault or faults the player has committed.

If the player is free to go, and is wearing the crime-fighting costume, 
the game is won. We tell you how that's reported in the next chapter, 
where we finish off the design.