FAQ for Alan v2 (obsolete)

This is the FAQ (list of Frequently Asked Questions) for the Alan Adventure Language System. If you have further questions that might fit in here please This email address is being protected from spambots. You need JavaScript enabled to view it..

Could you please give an example of how I create an actor?
Can an object contain something not an object?
Can an object contain itself?
Can an actor change an attribute of the hero?
Can an actor give or steal an object?
Can a verb be applied to both actors and objects?
How come my DEPENDING ON RANDOM x TO y doesn't work like I think it should?
How about time?
Why are there no title screen, tool bar and other sexy stuff?
Why does the compiler messages scroll off the screen so fast?
Why doesn't the Alan compiler find my files under Windows?
The ALAN compiler messages scroll off my screen before I can read them...
How can I draw a map?
What's all this about DPMI?
No coprocessor?
Why does my MAC version just die?

QUESTION: Only the JUNGLE example declares an actor, and it doesn't use a script. (I was hoping the tiger would be an actor.) I would like to see an example script, and I wonder whether it can be made responsive to something the hero says or does?

Paul de Anguera (This email address is being protected from spambots. You need JavaScript enabled to view it.)

ANSWER: A possible script in the JUNGLE example could be:

	ACTOR tiger AT northern_path
	    SCRIPT hunting
	        STEP
	            "A hungry tiger walks along the path
	             and disappears to the south."
	            LOCATE tiger AT southern_path.
	            "From the north a hungry tiger appears."
	        STEP
	            "The tiger takes a sniff at you before continuing
	             south."
	            LOCATE tiger AT clearing.
	            MAKE tiger sleeping.
	            USE SCRIPT sleeping.
	    SCRIPT sleeping
	        STEP WAIT UNTIL hero HERE
	            "As if aroused by your appearance the tiger turns
	             in its sleep."
	        STEP
	            "Suddenly the tiger is completely awake, staring
	             directly at you. In his eyes you can see his
	             hunger."
	            MAKE tiger NOT sleeping.
	END ACTOR tiger.

In this simple example the tiger is aroused by the hero entering the clearing where he is sleeping.

Some short examples can also be found in the manual. And there is an example featuring Floyd, the robot from Planetfall, in the Etudes in the Alan examples directory of the IF Archives on ftp.ifarchive.org. NOTE however that the sources in the etudes have been around for a long time and possibly does not compile unaltered.

Actor interaction is one of the most problematic things in IF in general. Interacting with actors is usually implemented in Alan using player constructs like

> pat the tiger > ask the janitor about the car > tell susan to go home

The first example is rather simple and could be implemented by adding a verb to the tiger (handling the special case of patting the tiger, patting other things would not be possible unless the verb was generally available):

VERB pat
  DOES
    "Well, patting a tiger is a feat to admire, however
     the tiger is not so impressed!"
    MAKE tiger hungry.
    USE SCRIPT hunt FOR TIGER.
END VERB pat.

A script named 'hunt' also has to be implemented in the tiger to handle what it does when it hunts for something to eat. Note however that if the tiger simply would eat the hero, this can be handled directly in the verb body and does not necessarily imply an additional script.

QUESTION: Can an object contain an object of a different class (such as a bottle containing a genie or a miniature world)?

ANSWER: Alan does not support containment of anything other than objects. However it is wise to keep in mind that we do not necessarily have to build a complete simulation of the 'normal' world and its laws of physics etc.>

E.g. implementing a bottle containing a genie in a bottle would really only require some descriptional text for the bottle, an invisible genie (actor or object, see the manual for hints how to do this). A world inside a container can be implemented as a set of normal locations, the connection to the 'real' world being a special exit or, as in this example, verb:

OBJECT bottle ... VERB enter CHECK miniature_world IS visible ELSE "You can not fit in the bottle." DOES LOCATE hero AT miniature_center_square. END VERB enter. END OBJECT bottle.

QUESTION: Are there rules against recursive references, such as an object that ultimately contains itself?

ANSWER: Alan does not prohibit anything which will not lead to a run-time problem. The principle being that the player should not ever have the game crash on him.

Bugs, in the class of logical cliches, can not be ruled out by the language and compiler. So in this particular example you can have objects that are containers and place them in each other. The result is initially surprising and rather entertaining, thus left as an exercise for the reader.

QUESTION: Can an actor change an attribute of the hero (blessing him for example)?

ANSWER: All entities in an Alan 'program' are global, so their attributes are accessible from anywhere. Provided the 'blessed' attribute has been declared on the hero the following statement can be used from anyplace, including from a verb inside an actor or from a script:

MAKE hero blessed.

Making any actor blessed requires the attribute to be declared as a default actor attribute. The implications of being blessed must of course also be implemented, like changing descriptions or allowing new actions.

QUESTION:Can an actor give or steal an object? (in other words, can you get objects into or out of the inventory under program control?)

ANSWER:The LOCATE statement moves entities (e.g. objects) from wherever they are to the indicated position (location, container) without any restrictions (except for the case when the new position is in a container, in which case its limits are applied). In fact the standard 'take' and 'drop' verbs use program control to transfer object to and from the inventory.

There has also been some discussion on how to aid the author to prohibit a move out of a container, but no good solution has yet been found (probably a new section in the container will be needed). An example of this problem is when an actor carries an object and the hero/player takes it, the actor should get a chance to react.

QUESTION: How do I make a verb applicable to both actors and objects?

ANSWER: This was one of the key new features of Alan v2.7. An example is available as Verbs refering to actors and objects among the samples.

QUESTION: How come my DEPENDING ON RANDOM x TO y doesn't work like I think it should?

ANSWER: This is a bug in the DEPENDING ON statement (2.8). The DEPENDING ON statement was designed to only execute the expression once, but for several reasons (mainly temporary brain damage ;(, but it was aimed to preserve compatability between versions) it does evaluate the expression once for every case until it finds a match. This means that given:

DEPENDING ON RANDOM 1 TO 8 = 1 : "A one!" = 2 : "A two!" ELSE "A three and go!" END DEPEND.

will be executed as if it was equivalent to:

IF RANDOM 1 TO 8 = 1 THEN Â "A one!" ELSIF RANDOM 1 TO 8 = 2 THEN Â "A two!" ELSE Â "A three and go!" END IF.

This will execute "A one!" one out of 8, but "A two!" only in 1/8th of 7/8, which is less than one out of eight. This is because the RANDOM must first return something not a 1 to miss the first case and then, on the second evaluation, a two in order to catch that case. The more cases that you have the more squewed this distribution gets. This effect might also lead you into believing that RANDOM might return values not in the range.

Unfortunately it is impossible to fix this bug without making interpreters incompatible, so I have decided to leave it as it is for now.

The good thing is that it will work perfectly for any expression that yields the same value in consecutive evaluations, such as the value of an attribute.

WORKAROUND: Due to the last section above it is easy to make a work-around. Simply assign the value to an attribute and use that in the DEPENDING statement:

SET r OF o TO RANDOM 1 TO 8. DEPENDING ON r OF o =1 : "A one!" =2 : "A two!" ELSE "A three, and go!" END IF.

QUESTION: Does ALAN support built-in time capabilities ? A.k.a counting turns and converting them into passing minutes. Is there a way to display the time after each turn ?

ANSWER: Alan does not currently support this as built in functionality. However using a few lines of code turn counting and converting into time can be handled. In the same way you can use an event to automatically display it (or whatever you chose) each turn. E.g.

EVENT tick. INCREASE turns OF hero. IF minute OF clock = 59 THEN SET minute OF clock TO 0. INCREASE hour OF clock. ELSE INCREASE minute OF clock. END IF. "The time is now" SAY hour OF clock. "$$:$$" SAY minutes OF clock. END EVENT tick.

QUESTION: Although your compiler is better than AGT it lacks basic elements like title screen, instruction option and tool bar.

ANSWER: Well, the opinion on what are basic elements depends on if you focus on the visual appearance or the ability to support authoring. We have mainly focused on the 'basic elements' that are needed to support easy authoring.

This is not to say that we have not been thinking about things that would improve the visual appearance and make it more in the traditional style (i.e. look the same as all the other systems ;-)

QUESTION:I edit my files with Notepad under Windows and save them as text files. I can see the files in the directory but the ALAN compiler doesn't find them. Why is that?

ANSWER:Notepad under Windows can save files as ordinary textfiles that Alan can read and compile. However if you use the text file format when you save Notepad will always add a ".txt" extension (type). In windows this extension is the sole indication of what type the file is. So if you type the file name as "mygame.ala" in the dialogue box chances are that it ended up as "mygame.ala.txt". If you have the option "Show extensions of known file types" turned off you will still see a file with the name "mygame.ala" but it is shown as a text file icon. Try renaming the file in a MSDOS-command shell using

ren mygame.ala.txt mygame.ala

and retry the compilation.

The above also applies when saving files as text files using Word or similar programs. Get a real text editor program. There are many free ones on e.g. Winsite, Tucows or Download.com. My favorite is NT-Emacs, a NT/Windows port of the increadible Emacs editor. It is very, very powerful but can be a bit complex and frustrating to begin with.

QUESTION:The ALAN compiler messages scroll off my screen before I can read them. I tried piping them to a file but couldn't get it to work (wish this was Unix, not DOS). Is there an option or flag to make them go to a file or display a screen at a time?

ANSWER: All command line options are described in the manual, but can also be listed by using the '-help' option to the compiler. To handle error messages there are mainly two options which can be of use:

-listing <file> create a listing file with error messages
-cc show messages in short compact format

However the Alan compiler uses the standard error message channel (stderr instead of stdout, for you techies) for message output which on some system has been more trouble than it is worth. In the future it will use the standard output channel for this, which will make it easier to redirect (especially on the PC).

QUESTION:Maps are important; I've found that most people won't play D&D without one. Is there some way to display a diagram or invoke another program to do it? I thought of typing one with graphic keys but am hoping for something nicer.

ANSWER: Alan is a text-only system, but there is a method to call external programs, the SYSTEM statement. This could be used for example to call a program to show a detailed map. But use of this feature should be most restricted as any calls to standard MS-DOS programs will probably not work on an Amiga... As an author you are responsible to make your games as portable as possible, in this case that your map showing program is available on all platforms.

You could also try to draw a map using ANSI character art. This is reported to work on most platforms.

QUESTION: When I try to run ARUN or ALAN on my PC I get: "Load
error:no DPMI - Get csdpmi*b.zip"
What's going on? And where can I get this file?

ANSWER: Some early versions of Alan for the PC was built using DJGPP, the excellent PC port of the GNU C-compiler environment, GCC, by D.J.Delorie. This produces true 32-bit virtual memory applications, a feat which on PC's require something called a DPMI host. All Windows versions have one but if you run plain DOS you might miss one. There is a free one called CWSDPMI which is distributed with DJGPP and can be down-loaded from any SimTel mirror such as: ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2misc/

QUESTION: Why does Alan stop with a "No coprocessor" message on my 386?

ANSWER: See the answer to the previous question. In this case the installation of emu386.dxe is reported to remedy the problem.

QUESTION: The MAC version does not seem to work correctly. I try to compile the Saviour example but it just leaves a saviour.txt file and then exits without any message.

ANSWER: For early versions of the Mac-port this, as well as a number of mysterious unexpected terminations of the Alan compiler (most often without any messages at all), has been reported to be remedied by making the memory allocation for the Alan compiler larger. The requirements depends very much on the size of your game.

Alan Interactive Fiction Language

FAQ for Alan v2 (obsolete)

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