Functional programming, though far from new, has gained much traction recently. Functional programming characteristics have started to appear in the PHP world, too. Microframeworks such as Silex and Slim, middleware architectures such as Stack and even standards such as PSR-7 rely on concepts such as lambdas, referential transparency and immutability, all of which come from functional programming. I’ll give you a crash course in Erlang, a pragmatic functional language to make you feel familiar with the functional paradigm. By comparing code samples between Erlang and PHP, you’ll find out how you can employ functional programming in your PHP applications where appropriate. You’ll see that functional programming is nothing to be scared of. On the contrary, understanding its concepts broadens your programming horizon and provides you with valuable solutions to your problems.