The second lesson looks at some examples of common functors, including the IO functor and tuples. We also work through some examples using the text package, some cases where we have to fmap twice, and look at how to make a custom “pair” functor when you want a pair of values of the same type.
The seventh lesson gets to “chunked” response encoding. This is an important concept to understand for having a mental model of how to curtail a server’s memory usage, and it’s a good technique to keep in your toolbox if you ever have to design a network protocol yourself. It also gives us a great excuse to play with lazy I/O in Haskell.