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The key to solving complex design 
problems is to break them down into 

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smaller pieces. 
Now, the recipes already do that of 

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course. 
The data recipe breaks data design down 

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into individual steps. 
The function recipe does the same, and 

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so, does the world recipe. 
But sometimes we need more decomposition 

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than that. 
Sometimes we need to break a data 

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representation into multiple types, or a 
function design in the multiple 

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functions. 
Now, we've seen a couple examples of that 

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already of course. 
Whenever we have the reference rule, then 

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we end up with a natural helper function. 
And the world's recipe also breaks the 

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design down into multiple handlers. 
But this week, we're going to look at 

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more examples of how we break types and 
functions down into multiple types and 

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multiple functions. 
The week is broken into two parts. 

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In the first part, we're going to look at 
rules for helper functions operating on 

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the kinds of data we've already seen. 
In the second part, we're going to 

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introduce a new kind of arbitrary size 
data. 

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And that kind of data definition itself 
automatically introduces helpers into the 

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functions that operate on the data.