Alice through the VDU
Timely crib for a trip with the Time Lords
LORDS of Time was designed by Sue Gazzard, a Harrow housewife
and, judging from the peculiar way the player moves through time,
a Dr. Who fan.
This adventure from Level 9 had an extra sheet of hints for
the reviewer as well as the usual neat booklet. Having read the
extra hints on how to operate the time machine - in this case
a grandfather clock - my reaction was that I definitely needed
the crib.
You have to wind, turn and push things before you can visit
any of the nine time zones, which the booklet tells you to tackle
in numeric order. This, it says is to ensure that you have the
objects needed to solve the puzzles.
Of course it doesn't ensure anything of the kind, because you
are limited to carrying only four objects and there are about
80 objects to choose between.
Of these 18 are treasures and nine are special ingredients,
like an Ivory Tusk, Dinosaur Egg and Evil Eye, which you have
to throw into a cauldron.
As expected, the program fills the machine with compiled a-code
and compressed text so there is little scope for cheating.
Like Snowball, it plays a nice little Vivaldi tune as it loads
— a clever bit of interrupt programming — and then up comes the
message that Father Time has "chosen youn (sic) to help defend
history against nine evil Time Lords".
First time in I got an hourglass, a candle and a box of matches
and then asked for a LIST of what I was carrying. The answer was
"an old mattress".
Now for a quick look at the nine zones, so let's go into the
clock to find them. The periods we can choose are Present, Ice
Age, Stone Age, Vikings, Mediaeval, Tudor, Future, Roman and Far
future (where I got stuck, so QUIT).
Now it's fairly obvious when some of the special ingredients
must be. The ivory tusk must belong to the mammoth in the Ice
Age, but the sabre-tooth tiger caused trouble, so back to the
Present, into the cottage and get the Masai spear off the wall.
Check that it's sharp and now try KILL TIGER WITH SPEAR, which
gets the response: "Only a fool would attack a Masai spear".
One of the tricks I mentioned in a previous article is to check
if something exists. This program has some weird responses to
this method like:
GET EYE: "You can't see a tightly closed box".
OPEN WALL PANEL (because the wall panels sound hollow in the
Tudor mansion): "You can't see a wall of ice blocking the
way south".
GET C AND (short for candle): "You can't see a silver candelabra".
EXAMINE MATCH: "2tches are left".
The program is riddled with these interesting slips because
it is trying very hard to make sense of what you say. Many adventures
insist on exact words, otherwise they respond with, "I don't
understand", or, "You can't do that".
You see, the more ambitious the syntax and semantic analyser
the more likely you are to get odd answers which the designers
can't always predict.
The game is complex but it does not appear to have any real
time paradoxes. I don't count dinosaurs living in the Stone Age
which, we are told, was caused by the Time Lords' meddling.
A true time paradox should be caused by the player altering
the Future whenever he alters the Past. If say, he drops an object
somewhere he should find its decayed remains in a future time
zone.
Such complexity is very difficult to design into adventures
which, so far, only deal with where objects are and not when.
But maybe someday someone can come up with the equivalent of
Isaac Asimov's "End of Eternity" or Ray Bradbury's short
story "Tyrannosaurus Rex", where accidentally crushing
a butterfly in the past totally alters the future.
As usual, because I can't get at the text, I haven't got very
far with this game. The text has been compressed and to give some
idea of how this is done, I will discuss some simple examples.
Take the sentence: the cat sat on the mat = 22 characters
A text compressor scans this and finds that "the"
and "at" are common strings of characters so it replaces
them with special characters like "#" and "@"
thus: #c@s@on#m@ = 10 characters
The text expander gets this string and uses some simple rules
like:
• If special character then expand.
• If first character of sentence then make it upper case.
• If upper case character then output lower case + " ".
If you have an enormous amount of text, like the Bible, then
another method is to identify and code into single bytes the (1-255)
most common words and use the byte "0" to mean "output
the next character as literal Ascii".
In this way most of the spaces disappear as well, and the text
can be roughly halved.
Whichever method is chosen a further compression can now be
made on the new string of bytes by applying some information theory
first discussed by Claud Shannon, an American cryptologist in
the Second World War. In a classic paper he explained, for the
first time, why codebreaking is possible.
The reason is that all natural languages are extremely redundant
— only about 25 per cent of most text is strictly necessary. To
illustrate this redundancy Shannon asked people to guess, one
by one, the characters in the following: There is no reverse on
a motorcycle
On average people guess two thirds of the letters in this sentence,
particularly if they spot the semantic clue at "motorc"
and don't guess motorcar.
Information theory has many applications and can treat ALL forms
of communication as a problem in statistics, giving precise measurements
of the amount of information conveyed and the efficiency of the
machines that handle the information.
When we transmit messages the frequency of the characters can
be exploited by giving short codes to the more frequent symbols.
This is most evident in the Morse code where the letter E is the
most common in most European languages and therefore has the shortest
code.
Now consider a first pass compressed adventure text. Given only
the frequencies of symbols in this new language, how can we design
for optimum transfer properties?
The answer is stated without proof (log2 means log to the base
2): On the average H=-sum i=l to N of Pi*log2(Pi) bits should
correspond to each symbol where Pi is the probability of the occurrence
of the i-th symbol. The expression is called the entropy where
H is Boltzmann's function.
A "bit" is a binary digit (0 or 1). Shannon had already
shown before the war that it does not matter what number system
is used in the calculations. We tend to use the base 10 decimal
system, but it is simpler to build binary electronic circuits,
which explains the log2 in Shannon's equation.
To show it working, suppose we have a simple language containing
only four symbols A, B, C, D with probabilities 1/2, 1/4, 1/8,
1/8 respectively. A sentence in this language might be: ACBADABADAABACBA
The entropy of this language is: H=-(1/2*log2(1/2)+ 1/4*log2
(1/4)+2/8*log2(1/8)) which is 7/4 bits per symbol.
If we represented each symbol with two bits - for example, A=00,
B=01, C=10, D=11 - then the above result says we are not being
efficient. We are not taking account of the fact that A is more
frequent than the other symbols.
A better code is A=1, B=01, C=001, D=000 because then we can
transmit the original sentence in 28 bits:
1001011000101100011011001011 rather than the 32 bits required
by the two bit code.
Level 9 use these techniques to produce their big adventures.
Lords of Time has well over 200 rooms, 750 messages and about
80 objects, plus dozens of puzzles to solve.
Compared with the early micro adventures of five years ago,
which usually took about a day to solve, it's about nine times
bigger and should take at least nine times longer to finish.
This raises a question I've been asked many times: how to solve
adventures in general. The simple answer is that nobody can teach
anybody how to think, just as nobody can teach us how to walk.
All I can do is give some guidelines and simple techniques,
such as constructing a map with a matrix which I'll discribe next
month.
Don't forget
to construct a map
You'll have to allow for 12 directions in Lords of Time because
IN and OUT are possible. Also examine every object and search
every room because the program does not always tell you everything
about what you can see.
Another trick is to carry four objects and just try to GET EVERYTHING
whenever you reach a new room, because the program gives a rather
more detailed description of all the things you can't get.
If you are an absolute beginner and have never played an adventure
before then I suggest you start with one of the simple little
classics by Scott Adams.
One of his first was Pirate Adventure, written back in 1978,
which is still on sale. Adams published a listing of the game
in Byte in December 1980 which, if you have the tenacity, can
be reduced to about 350 BBC Basic statements.
It has 26 rooms, 75 messages and about 30 objects. All in all,
it's only one-ninth the size of Level 9 games and can usually
be solved in 140 moves by a beginner in about two days. Nevertheless,
it is an amusing little game and ideal for children.
For those of you who have never been in a "twisty little
maze" I have written a program to give you some idea of what
they are like, and leave it to you to find out how to solve it.
Note that you can enter multiple commands like N.S.GET.LIST.SCORE
and that, once again, there is a prize for the best explanation
of how to get the money and take the exit.
Alice
