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13.2 Lambda Expressions

A lambda expression is a function object written in Lisp. Here is an example:

(lambda (x)
  "Return the hyperbolic cosine of X."
  (* 0.5 (+ (exp x) (exp (- x)))))

In Emacs Lisp, such a list is a valid expression which evaluates to a function object.

A lambda expression, by itself, has no name; it is an anonymous function. Although lambda expressions can be used this way (see Anonymous Functions), they are more commonly associated with symbols to make named functions (see Naming a Function). Before going into these details, the following subsections describe the components of a lambda expression and what they do.