infocom/articles/NZT-parser.txt

PARSER???
by Stu Galley
(The Status Line; Spring 1989; page 2)
Copyright 1989 (c) Infocom
Transcribed by Graeme Cree

     What is a parser anyway, and why should it matter to you?  Almost any 
dictionary can answer the first question, and I'm here to tell you about 
the second one.
     As the dictionary states, a parser is something that takes apart a 
sentence, word by word, and determines what the words mean, and then what 
the sentence means.  If you ever diagrammed a sentence for an English class, 
then you were parsing.  But it's a lot easier for YOU to parse English than 
it is for a machine, because you've had a lot more practice at it, and you 
started life with a certain natural ability to do it.
     At Infocom, I've been working on a program that will parse your commands 
and pass on their "meaning" to an interactive story.  This program is a part 
of ZORK ZERO, ARTHUR, and SHOGUN, as well as future Infocom products that 
may want to understand more complex sentences.  In a way, I'm like the 
recording engineer for your favorite rock album, because my job is to make 
sure that the artists' talent comes through to you as clearly as possible.  
If the guitarist wants more reverb...I mean if the implementor wants 
adverbs to work in his story, then I provide it.  The better I do my job, the 
less you notice it!
     Almost anyone can write a simple parsing program, just as almost 
anyone can make simple recordings on their boom box.  A simple parser could 
parse any two-word sentence, by calling the first word a verb and the second 
one a noun.  If it didn't know the verb, or if the noun wasn't the name of 
something in the room, then it would give up.  Some simple adventure games 
work exactly that way.
     Until now, Infocom's thirty-odd interactive stories have all used the 
parser that evolved from ZORK I.  But each  new story needed some new 
features in the parser, and so it grew more clever, but also harder to fix 
and improve.  Eventually, we decided to build a new parser from scratch, 
using the theory of computational linguistics.  (Technically speaking, we 
used an ATN algorithm with a LALR grammar and one-token look-ahead.)
     So what does this mean to you?  It means that you can converse with our 
interactive fiction more simply than ever, and we can easily add features 
that you've never seen before.  For example, ZORK ZERO notices if you seem 
to be having trouble with the parser, and it offers helpful suggestions, 
such as sample commands.  And in SHOGUN, you can use a wider range of 
sentences, including statements and questions, to converse with the 
characters you'll meet.  In the future, we may develop new kinds of 
products, able to "talk" with you about many topics; our interactive fiction 
could becomre much more than mazes and mysteries!