Info Catalog elisp: Lambda Expressions elisp: Simple Lambda

elisp: Lambda Components

 
 12.2.1 Components of a Lambda Expression
 ----------------------------------------
 
 A lambda expression is a list that looks like this:
 
      (lambda (ARG-VARIABLES...)
        [DOCUMENTATION-STRING]
        [INTERACTIVE-DECLARATION]
        BODY-FORMS...)
 
    The first element of a lambda expression is always the symbol
 ‘lambda’.  This indicates that the list represents a function.  The
 reason functions are defined to start with ‘lambda’ is so that other
 lists, intended for other uses, will not accidentally be valid as
 functions.
 
    The second element is a list of symbols—the argument variable names.
 This is called the “lambda list”.  When a Lisp function is called, the
 argument values are matched up against the variables in the lambda list,
 which are given local bindings with the values provided.  Local
 Variables.
 
    The documentation string is a Lisp string object placed within the
 function definition to describe the function for the Emacs help
 facilities.  Function Documentation.
 
    The interactive declaration is a list of the form ‘(interactive
 CODE-STRING)’.  This declares how to provide arguments if the function
 is used interactively.  Functions with this declaration are called
 “commands”; they can be called using ‘M-x’ or bound to a key.  Functions
 not intended to be called in this way should not have interactive
 declarations.  Defining Commands, for how to write an
 interactive declaration.
 
    The rest of the elements are the “body” of the function: the Lisp
 code to do the work of the function (or, as a Lisp programmer would say,
 “a list of Lisp forms to evaluate”).  The value returned by the function
 is the value returned by the last element of the body.
 

Info Catalog elisp: Lambda Expressions elisp: Simple Lambda