The manual, hand-rolled coordinate parsing function we made last time is already pretty complicated, and capturing every edge case will make it more complicated still.

But that’s not even the worst part. The worst part is that this parse function is a one-off, ad hoc solution to parsing the very specific format of latitude/longitude coordinates. There is nothing inside the body that is reusable outside of this example.

We’re definitely seeing how tricky and subtle parsing can be, and it’s easy to end up with a complex function that would need to be studied very carefully to understand what it’s doing, and even then it would be easy to overlook the potential bugs that lurk within.

Let’s back up and formally state what the problem of parsing is and analyze it from the perspective of functional programming and functions.