How did you “flip the switch” in your brain to the functional mindset?

For me, one thing that changed is that I now tend to focus more on the data *transformations* rather than on the data itself. I tend now to group similar transformations into modules. (Before, as an OO programmer, I would have thought of each module as a class of objects, so I would have grouped everything that acts on that object or that the object does into one class.) Eventually you want to build a chain of transformations that takes the input and produces the output you want.

Another way to visualise it: Instead of thinking of the steps to solve a problem, think of the solution as a series of definitions. Write a definition (an equationof of the result you want in terms of simpler things. Write definitions of those simpler things in terms of things that are even simpler. And so on, until you can build a pyramid of definitions that defines the final output in terms of the input.

I found it helpful to post a few small code samples on this forum, and to ask for suggestions for a better implementation.

Good luck!