In his latest post Mathias Verraes looks at "higher level programming" in PHP. Higher order programming is a style of programming that uses components (like functions, modules or objects) as values.

Let’s have some fun with higher order programming in PHP. I’ll start by showing how to program with Lambdalicious (or λlicious for friends) and introduce the real meat along the way. Don’t worry too much about the dark magic that may appear to power some of the features of Lambdalicious. It’s on GitHub if you’re curious. Just follow along and keep track of all the functions.

He breaks his examples up into (lots of) different examples, each with example code:

• Atoms
• Lists
• Functions
• Conditionals
• Loops & List Processing
• Deduplication
• Filter and Reduce
• Functions returning functions
• Partial Function Application
• Composition
• Piping

He finishes off the post talking about Lambdalicious and how, in reality, it's just not suitable for anything useful as written in PHP. The language just doesn't have the right functionality to make it work sufficiently...even HHVM.