HtDP 9

Compounds are for a known number of things, what if we don't know how many there are?

How could we break down any number of things into a mixed data definition?

We'd know what to do if there was 0, if there was 1, etc

How could we get any number? 1 More! And then some...
- this is a structure reference just like we've seen before
- but a little funny, because it is a reference to the same thing

Try list of planets (strings)

Write length
=> num

Write sumLength
=> num

Write averageLength
=> sum / len

Write containsLessThan4
=> bool