Common LISP Hints: Special forms

## 10. Special forms

There are a number of special forms which look like function calls but aren't. These include control constructs such as `if` statements and do loops; assignments like `setq`, `setf`, `push`, and `pop`; definitions such as `defun` and `defstruct`; and binding constructs such as `let`. (Not all of these special forms have been mentioned yet. See below.)

One useful special form is the `quote` form: `quote` prevents its argument from being evaluated. For example:

> `

>     > (setq a 3)
>     3
>     > a
>     3
>     > (quote a)
>     A
>     > 'a                    ;'a is an abbreviation for (quote a)
>                             ;it's the quote next to the enter key
>                             ;on a qwerty keyboard
>     A

> `

Another similar special form is the `function` form: `function` causes its argument to be interpreted as a function rather than being evaluated. For example:

> `

>     > (setq + 3)
>     3
>     > +
>     3
>     > '+
>     +
>     > (function +)
>     #<Function + @ #x-fbef9de>
>     > #'+                   ;#'+ is an abbreviation for (function +)
>     #<Function + @ #x-fbef9de>

> `

The `function` special form is useful when you want to pass a function as an argument to another function. See below for some examples of functions which take functions as arguments.