Land of Lisp

Chapter 6.5. lambda: A Function So Important It Deserves Its Own Chapter

It’s impossible to overstate the importance of the lambda command in Lisp. In fact, this command is pretty much the entire reason that Lisp exists in the first place.

What lambda Does

In short, lambda lets you create a function without giving it a name. For example, let’s say we create a half function that takes a number and divides it in half. Until now, we’ve written such a function this way:

(defun half (n)
    (/ n 2))

It turns out that, in Lisp, functions are actually values that we can view and pass around just as if they were numbers or lists. An experienced Lisp programmer ...