Lisp语言驱动Autocad自动化开发：应对技术挑战的利器

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在当今信息化社会，计算机和软件在我们的日常生活中扮演着至关重要的角色。随着科技的进步和人们对技术的日益期待，软件开发者面临着巨大的压力，不仅要满足用户对新特性和功能的无尽需求，还要在有限的时间和资源下快速实现这些创新。在这个背景下，Lisp语言作为一款独特且强大的开发工具，被用于Autocad等CAD软件的二次开发，展现出其独特的优势。 Lisp，全称Common Lisp，是一种功能强大且灵活的编程语言，它的设计初衷是为了支持动态编程、函数式编程以及极简主义原则。这种语言的特点包括高度可扩展性、自修改性和高阶函数，使得它在处理复杂任务时表现出色，尤其适合于自动化和集成系统构建。在Autocad二次开发中，Lisp语言的应用主要体现在以下几个方面： 1. **模块化编程**：Lisp允许程序员通过编写小程序（也称为宏）来扩展Autocad的功能，这些宏可以像模块一样组合和复用，大大减少了代码量并提高了开发效率。 2. **动态性与灵活性**：由于Lisp是动态类型的语言，开发者可以在运行时修改程序结构，这在处理CAD环境中可能遇到的非预期情况时非常有用。此外，Lisp的交互式环境让用户能够实时测试和调试代码，提高了问题解决的速度。 3. **高阶函数**：Lisp支持函数作为一等公民，这意味着函数可以被赋值、传递和作为参数。这对于处理Autocad中的复杂几何操作和数据处理非常有效，可以编写出简洁而高效的解决方案。 4. **自动化脚本**：利用Lisp，开发者可以编写自动化脚本来自动执行重复的任务，如导入数据、修改对象属性或执行绘图操作，从而节省大量时间。 5. **与CAD接口**：Lisp与Autocad的API紧密结合，使得开发者可以直接操控Autocad的对象模型，实现深度定制和集成，提升了CAD应用的生产力。然而，使用Lisp进行Autocad二次开发也需要注意一些挑战，比如学习曲线相对较陡峭，对于初学者来说可能会感到不适应；另外，由于其动态特性可能导致内存管理问题，如果不善加控制，可能会降低性能。但总体而言，Lisp凭借其强大的功能和适应性，为Autocad和其他CAD软件的高级定制提供了有力的工具。在投资和技术发展日益重视结果的时代，Lisp作为一门能满足未来技术挑战的语言，值得开发者深入研究和掌握，特别是在CAD领域，其潜力尚未完全释放。随着开发者们不断探索和优化，Lisp在Autocad二次开发中的应用将更加广泛，推动CAD软件向着更加智能化和高效化的方向发展。

8 CHAPTER 2. OPERATING A CL DEVELOPMENT ENVIRONMENT

2.3 Running CL inside a Text Editor

A more powerful way of developing with CL is by running it from within a Unix (or DOS)

shell that is running inside a buﬀer in a powerful text editor, such as Gnu Emacs

. One

advantage of this approach is that the editor (in our example, Emacs) keeps a history of

the entire session: both the expressions the programmer has typed, as well as everything

that CL has printed. All these items can be easily reviewed or recalled.

2.3.1 A Note on Emacs and Text Editors

To develop using Common Lisp, you can, of course, use any text editor of your choice,

although Emacs happens to be especially synergistic for working with CL, for reasons we

will discuss later. With a bit of practice, you will ﬁnd that the combination of Emacs and

Allegro CL provides a more powerful and conve nient development environment than any of

today’s ﬂashy “visual programming” environments. If you are used to working with the “vi”

editor, Emacs come s with several “vi” emulation modes which you may want to experiment

with on a transitional basis. If you are used to working with a standard Windows-based

text editor, you will ﬁnd a smooth transition to Emacs.

This guide provides examples using Gnu Emacs.

To work with CL in an Emacs shell buﬀer, you should be reasonably familiar with the

text editor. If you are completely new to Gnu Emacs, go through the Emacs Tutorial,

available under the “Help” menu at the top of the Emacs window.

2.3.2 Emacs Terminology

As you will learn in the Emac s Tutorial, when working with Emacs you make frequent use

of key chords. Similar to “chords” on a piano, keychords can allow powerful text processing

with relatively few sequential keystrokes.

They are key combinations involving holding down the Control key and/or the Meta

key, and pressing some other regular key.

See Appendix C for information on which keys represent Control and Meta on your

keyboard, and how you can customize these. To begin, try using the key labeled “Control”

for Control and the keys labeled “Alt” (or the diamond-shaped key on Sun keyboards) for

Meta. If your keyboard has a “Caps Lock” key to the left of the letter “A,” you should

consider remapping this to function as Control, as explained in Appendix C.

This guide uses the following notations to indicate keychords (identical to those refer-

enced in the Emacs Tutorial):

• M-x means to hold down the Meta key, and press (in this case) the “X” key

• C-x means to hold down the Control key, and press (in this case) the “X” key

• C-M-q means to hold down the Control key and the Meta key at the same time , and

press (in this case) the “Q” key

Gnu Emacs comes pre-installed with all Linux systems, and for other systems should come as part

of your Allegro CL distribution. In any case, Emacs distributions and documentation are available from

http://www.gnu.org

10 CHAPTER 2. OPERATING A CL DEVELOPMENT ENVIRONMENT

2.4 Running CL as a subprocess of Emacs

An even more powerful way of developing with Allegro CL is by running it within Emacs

in conjunction with a special Emacs/Lisp interface provided by Franz Inc. This technique

provides all the beneﬁts of running in an Emacs shell as outlined above, but is more powerful

because the Emacs-CL interface extends Emacs with several special commands. These

commands interact with the CL process, making the editor appear to be “Lisp-aware.” The

combination of Emacs with the Emacs-CL interface results in a development environment

whose utility approaches that of the vintage Symbolics Lisp Machines, which many Lisp

aﬁcionados still consider to be technology advanced well beyond anything produced today.

Complete do c umentation of the Emacs-CL interface can be viewed by pointing your

web browser at: file:/usr/local/acl62/doc/eli.htm (you may have to modify this

pathname to point to your actual installed location of Allegro CL (acl62)).

2.4.1 Starting the CL subprocess within Emacs

To enable your Emacs to function in the proper manner, place the following expressions in

a ﬁle named .emacs in your home directory:

(setq load-path

(cons "/usr/local/acl62/eli" load-path))

(load "fi-site-init")

As above, you may have to modify this pathname to point to your actual installed location

of Allegro CL (acl62). Once you have added these lines to your .emacs ﬁle, you should be

able to restart emacs, then issue the command:

M-x fi:common-lisp

to start CL running and automatically establish a network connection between the Emacs

process and the CL process (in theory, the two processes could be running on diﬀerent

machines, but in practice they usually will run on the same machine). Accept all the

defaults when prompted.

You can also start emacs with the CL subprocess automatically from a terminal window,

by invoking emacs with an optional “function” argument, as follows:

emacs -f fi:common-lisp

This will start Emacs, which itself will immediately launch CL.

2.4.2 Working with CL as an Emacs subprocess

Once you have started CL within Emacs, you will be prese nted with a special buﬀer named

*common-lisp* which in many ways is similar to simply running CL within a shell within

Emacs as above. But now you have several more capabilities available to you, as outlined

in Table 2.1.

To summarize, the Lisp-Emacs interface adds capabilities such as the following to your

development environment:

2.4. RUNNING CL AS A SUBPROCESS OF EMACS 11

Keychord Action Emacs-Lisp function

C-M-x Compiles and loads

the function near the

Emacs point

fi:lisp-eval-or-compile-defun

C-c C-b Compiles and loads

the current Emacs

buﬀer

fi:lisp-eval-or-compile-current-buffer

M-A Shows the Argument

List for a CL function

fi:lisp-arglist

C-c . Finds the deﬁnition

of a CL object

fi:lisp-find-definition

Table 2.1: Common Commands of the Emacs-Lisp Interface

• Start and stop the C L process using Emacs commands

• Compile and load ﬁles into the running CL process, directly from the open Emacs

buﬀer you are editing (no need explicitly to save the ﬁle, call the compile-file

function, then call the load function, as with the “in-a-shell” techniques above)

• Query the running CL process for information about objects currently deﬁned in it

— for example, querying the CL, directly from Emacs, for the argument List of a

particular function

• Run multiple read-eval-print loops, or listeners, in diﬀerent threads of CL execution,

as Emacs buﬀers

• Compile and load speciﬁed sections of an open Emacs buﬀer

• Locate the source code ﬁle corresponding to any deﬁned CL object, such as a function

or parameter, and automatically open it in an Emacs buﬀer

• Perform various debugging actions and other general CL help capabilities, directly

from within the Emacs session

In short, Emacs becomes a remarkably powe rful, inﬁnitely customizable, CL integrated

development environment.

2.4.3 Compiling and Loading a File from an Emacs buﬀer

Try it: Try starting Emacs with a CL subprocess as outlined above. If you have trouble,

consult the URL listed above for complete instructions on running the Lisp-Emacs interface.

Once you have Emacs running with a CL subprocess, you should have a buﬀer named

*common-lisp*. If your Emacs session is not already visiting this buﬀer, visit it with the

command C-x b *common-lisp*, or select *common-lisp* from the “Buﬀers” menu in

Emacs (see Appendix C for instructions on how to set up a “hot key” for this and other

common tasks when working with the Emacs-Lisp interface).

12 CHAPTER 2. OPERATING A CL DEVELOPMENT ENVIRONMENT

Now, split your Emacs frame into two windows, with the command C-x 2. In both

windows you s hould now see *common-lisp*. Now move the point

to the other window

with C-x o, and open the hello.lisp ﬁle you created for the previous exercise

. If you

don’t have that ﬁle handy, create it now, with the following contents:

(defun hello ()

(write-string "Hello, World!"))

Now, compile and load the contents of this function deﬁnition with C-M-x. Finally, switch

to the *common-lisp* window again with C-x o, and try invoking the hello function by

calling it in normal Lisp fashion:

CL-USER(5): (hello)

Hello, World!

"Hello, World!"

You should see the results printed into the s ame *common-lisp* buﬀer.

Try it: Now try the following: go back to the hello.lisp buﬀer, make an edit to

the contents (for example, change the String to "Hello, CL World!"). Now c ompile the

buﬀer with this change (Note that you do not necessarily have to save the ﬁle). Finally,

return to the *common-lisp* buﬀer, and try invoking the function again to conﬁrm that

the redeﬁnition has taken eﬀect.

You have now learned the basic essentials for working with the Emacs-Lisp interface.

See Appendix C for more information about Emacs customization and convenient Emacs

commands speciﬁc to the Lisp editing mode.

2.5 Integrated Development Environment

Some CL implementations support or integrate with an IDE, or Integrated Development

Environment. Such environments provide visual layout and design capabilities for User

Interfaces and other graphical, visual techniques for application development. For example,

such a system is available for Allegro CL on the Microsoft platforms. The details of these

systems are covered in their own documentation and are beyond the scope of this guide.

2.6 The User Init F ile

When CL begins execution, it usually looks for an initialization ﬁle, or “init” ﬁle, to load.

When CL loads this ﬁle, it will read and evaluate all the commands contained in it.

The default name and loc ation for this initialization ﬁle is

.clinit.cl

In technical Emacs parlance, the point is the insertion point for text, and the cursor is the mouse

pointer.

Remember that pressing the space bar will automatically complete ﬁlenames for you when opening ﬁles

in Emacs.

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