Re: [clisp-list] Module Loading in Lisp

[Sam S. <sd...@gn...>]

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Hi,

Vagmi Mudumbai wrote:
> As I understand, there are many ways to do the the python equivalent

I don't know what python import does.
I hope a python expert will chime in.


> of an import in Lisp. You can either to a (load :filename) or (require
> :filename). There is also the (import ...) thingy for which I appear
> to need a (defpackage ... ) and (in-package ...). Given my Python

these are 3 separate functions:

1. LOAD: loads a specific file, i.e., evaluates forms contained in the
file one by one. file name argument should be a string or a pathname,
although CLISP also accepts symbols.
http://clisp.cons.org/impnotes/system-dict.html#loadfile
http://www.lisp.org/HyperSpec/Body/fun_load.html

2. REQUIRE: ensures that a module is present by loading a file, if it
has not yet been loaded. the module name argument should be a symbol or
a string. if you intend to use REQUIRE, you should have a PROVIDE form
in the module.
http://clisp.cons.org/impnotes/system-dict.html#require
http://www.lisp.org/HyperSpec/Body/fun_providecm_require.html

3. IMPORT: adds symbols ("names") to the internals of a package
("namespace"). I don't think you want to do this.
http://www.lisp.org/HyperSpec/Body/fun_import.html

> Say, I have a module called lib.lisp which has the single line.
> 
> (setf *var* 20)

you probably want DEFVAR or DEFPARAMETER here.

> I then have lib1.lisp, which has the following.
> 
> (require :lib)

if you do this, you should do (PROVIDE :LIB) in lib.

> (setf *var* 40)
> 
> I then have lib2.lisp which requires both lib and lib1.
> 
> (require :lib1)
> (require :lib)
> 
> Then the value of *var* when finally executing lib2 is 20 and not 40.
> I suspect that I am not following the lisp style of programming. If
> so, can you please point me in the right direction?

namespaces are orthogonal to filenames.

if you do (DESCRIBE '*VAR*), you will be told that *VAR* is a symbol in
package CL-USER - the default package.

if you want to create other packages, you need to do that explicitly
using DEFPACKAGE:

- ---- lib.lisp ---
(defpackage #:my-pack
  (:export #:*foo* #:bar))
(in-package #:my-pack)
(defvar *foo* 42)
(defun bar (x) (+ x *foo*))
(defun baz (x) (* x *foo*))
(provide "lib")
- ---- lib.lisp ---

- ---- bil.lisp ---
;; current package = CL-USER; "lib" stuff is not available
(print *package*) ; prints #<package common-lisp-user>

(require "lib") ; "lib" stuff is now available
(print my-pack:*foo*) ; prints 42
(print (my-pack:bar 7)) ; prints 49
(print (my-pack::baz 2)) ; print 84,
; need two columns "::" because baz is not exported from my-pack

(in-package #:my-pack)
(print (baz 3)) ; prints 126, now all my-pack internals are available
directly
- ---- bil.lisp ---


your best friend is the function FIND-ALL-SYMBOLS: if you are getting
the wrong behavior, you might be using the wrong symbol.
http://www.lisp.org/HyperSpec/Body/fun_find-all-symbols.html

in general, you might find it more profitable to ask general CL question
on the comp.lang.lisp newsgroup, see
http://clisp.cons.org/impnotes/faq.html#faq-help

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