How to make and use library with lisp (clisp)?

Question

In C/C++, I can make a library, and make it static one or dll using #include "" in source code, and -labc when linking. How do I have the same feature in lisp?

As an example of util.lisp in directory A. I define a library function hello.

(defpackage "UTIL"
  (:use "COMMON-LISP")
  (:nicknames "UT")
  (:export "HELLO"))

(in-package util)
(defun hello ()
  (format t "hello, world"))

And try to use this library function from main function.

(defun main ()
  (ut:hello))
(main)

I tried

clisp main.lisp A/util.lisp 

But, I got the following message

*** - READ from #: there is no package with name "UT"

• What's the equivalent of #include "" to use the library?
• What's the equivalent of -lutil to load the library? What's the command line for clisp/sbcl to use the library?
• And for defpackage, Is this equivalent to namespace?

ADDED

I just had to load the library.

(load "./A/util.lisp")

(defun main ()
  (ut:hello))

(main)

And run 'clisp main.lisp' works fine.

Answer 1

What you are looking for are called systems. Common Lisp's defpackage has nothing to do with this, and yes, it's about namespaces. Have a look at the HyperSpec, or the idiot's guide (see Xach's comment below) to read more about it.

You can restrict yourself to merely loading files, but usually, a system definition facility is used; mostly ASDF nowadays. A minimal example:

(defsystem my-system
  :name "my-system"
  :version "0.0.1"
  :author "myself"
  :license "LLGPL"
  :description "it's a system."
  :serial t
  :components ((:file "packages")
               (:file "stuff")
               (:file "more_stuff")))

Where packages.lisp would contain the package definition, stuff and more_stuff are the lisp or fasl files to be loaded. This system definition (usually named filename.asd) must be symlinked to (or located in) a directory contained in asdf:*central-registry* for ASDF to find your system. Then, you can load the system thusly:

(asdf:oos 'asdf:load-op 'my-system)

An alternative to this has been added in more recent versions of ASDF:

(asdf:load-system 'my-system)

Or, when using slime, by pressing ,l my-system RET.

Answer 2

You have to load util.lisp before main.lisp:

> (load "util.lisp")
> (load "main.lisp")
> (main)
hello, world
NIL

Practical Common Lisp has a good introduction to defining and using packages.

Answer 3

Common Lisp is an image base language, although usually to a lesser extent than Smalltalk. This means that you use a library by loading it into the image, using LOAD (if used explicitly the often in form (load (compile-file "your-file-here"))), or usually with a system definition facility like ASDF. The loaded code is then available for all code compiled/loaded in the future.

Packages are indeed namespaces. They deal with mapping strings to symbols only, they are not connected directly to files or functions or anything else. You received a package error because you attempted to load a file using a package before a file defining it.