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### 1.2 Organization

The Common Lisp package is organized into four main files:

`cl-lib.el`

  This is the main file, which contains basic functions and information about the package. This file is relatively compact.

`cl-extra.el`

  This file contains the larger, more complex or unusual functions. It is kept separate so that packages which only want to use Common Lisp fundamentals like the `cl-incf` function won’t need to pay the overhead of loading the more advanced functions.

`cl-seq.el`

  This file contains most of the advanced functions for operating on sequences or lists, such as `cl-delete-if` and `cl-assoc`.

`cl-macs.el`

  This file contains the features that are macros instead of functions. Macros expand when the caller is compiled, not when it is run, so the macros generally only need to be present when the byte-compiler is running (or when the macros are used in uncompiled code). Most of the macros of this package are isolated in `cl-macs.el` so that they won’t take up memory unless you are compiling.

The file `cl-lib.el` includes all necessary `autoload` commands for the functions and macros in the other three files. All you have to do is `(require 'cl-lib)`, and `cl-lib.el` will take care of pulling in the other files when they are needed.

There is another file, `cl.el`, which was the main entry point to this package prior to Emacs 24.3. Nowadays, it is replaced by `cl-lib.el`. The two provide the same features (in most cases), but use different function names (in fact, `cl.el` mainly just defines aliases to the `cl-lib.el` definitions). Where `cl-lib.el` defines a function called, for example, `cl-incf`, `cl.el` uses the same name but without the ‘`cl-`’ prefix, e.g., `incf` in this example. There are a few exceptions to this. First, functions such as `cl-defun` where the unprefixed version was already used for a standard Emacs Lisp function. In such cases, the `cl.el` version adds a ‘`*`’ suffix, e.g., `defun*`. Second, there are some obsolete features that are only implemented in `cl.el`, not in `cl-lib.el`, because they are replaced by other standard Emacs Lisp features. Finally, in a very few cases the old `cl.el` versions do not behave in exactly the same way as the `cl-lib.el` versions. See Obsolete Features.

Since the old `cl.el` does not use a clean namespace, Emacs has a policy that packages distributed with Emacs must not load `cl` at run time. (It is ok for them to load `cl` at compile time, with `eval-when-compile`, and use the macros it provides.) There is no such restriction on the use of `cl-lib`. New code should use `cl-lib` rather than `cl`.

There is one more file, `cl-compat.el`, which defines some routines from the older Quiroz `cl.el` package that are not otherwise present in the new package. This file is obsolete and should not be used in new code.

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