So far, we've done quite a lot. 
We've done primitive data and primitive 
operations on that data. 
You learned, how to design functions 
recipe and how to design data recipe and 
you also learned, how to design worlds 
recipe. 
For designing world programs like 
animations and games. 
Most recently, we looked at compound data 
and learned how to use that in world 
programs. 
But so far all of the data definitions 
we've worked with have been what's called 
fixed size. 
And this week, we're going to add to our 
repertoire, working with arbitrary-size 
data. 
Now what do I mean by arbitrary-size 
data? 
I mean the kind of data we use when we 
want to represent an unknown amount of 
information. 
Information that we don't know upfront 
how much there will be. 
So, for example, if we ant to represent 
all of someone's favorite hockey teams, 
or all the students in a chorus. 
We just don't know, how many of those 
that will be, up front and that's what we 
need arbitrary sized data for. 
So, that's what we're going to work with 
this week. 
We'll look at how to do the data 
definitions. 
And we'll look at the effect that has on 
functions we design on that data.