With the rise of Javascript, and languages like Python and Ruby, functional programming is becoming more mainstream. Even Java seems to be getting closures in the next version, so does this leave PHP lacking behind or is there an unrealized potential hidden within?

He looks at a few different aspects of functional programming and sees how well PHP fits into them (like dynamic dispatch, binding a variable to a function and an implementation of currying for a function). This last option is the only "true" functional feature that PHP can realistically handle.