I learned to ‘programme computers’ long ago, almost before there was no “me” in ‘program’ and certainly before I knew how to ‘team’. I had a very brief and unsuccessful exposure to functional programming in LISP (not Lisp) then stopped. I did other ‘Data Processing’ things.
In recent years I’ve been working as an analyst, alongside people who write code according to the object model. I think I have a feel for objects but never having written code in an object-oriented language, I can’t be sure. I decided to try, in the Python language, then got distracted by the shiny Clojure language which is functional. I feel that right now I’m approximately equally confused by objects and functions, so I thought I’d write this quickly before I know what I’m talking about. I can come back later to laugh at my naivety, along with the rest of you.
Like the person who wrote this https://news.ycombinator.com/item?id=4246018 ,
“I’ve been watching some talks online recently by Rich Hickey of Clojure fame”
The post asks “So if I follow Hickey’s advice, how am I supposed to represent a book? As a vector of vectors of vectors of vectors of strings? If so, then how do I prevent a change in the representation of the Book from breaking client code?”
I found the question very interesting because representing ‘books’ in a functional language is exactly what I want to do. I think differently to the author because I’m not yet trapped inside the object paradigm. I can see that ‘book’ is a real-world class of objects, a very specific and limited implementation of the representation of a small subset of all the information in the world. That’s what my ‘book’ was going to be about and why I’m now playing with functions instead of writing it.
Objects are good at simulation of real life systems. They encapsulate small sub-systems of a process and it’s local data into an object. What I always struggled to understand was what you did with the data that didn’t want to be enclosed – “information wants to be free”. People seem to cope by inventing objects that don’t really exist: to be data shepherds.
Functions are good at abstraction. A book is a single output format from something much richer. That’s what I want to write. Data and processes are complex. Objects and functions are simplifying models; there may be others.
p.s. (not Lisp) Get it?
On The Outside 
Panic over. I’m ‘simply’ writing a functional program which returns a ‘vector of vectors of vectors of vectors of strings’ value. I should probably abstract that to a generalised book-writing machine. The best thing about this is that most people will think I’m joking.