What is AutoLISP?

Introduction

AutoLISP is a programming language built into Autodesk AutoCAD, derived from the LISP (LISt Processing) language. Introduced in AutoCAD in 1986, AutoLISP allows users to automate repetitive tasks, create custom commands, and extend the functionality of the CAD (Computer Aided Design) software.

Origins and LISP Heritage

AutoLISP has its roots in the LISP language, created by John McCarthy in 1958 at MIT. LISP is one of the oldest programming languages still in use today and was designed for list processing and artificial intelligence. Autodesk adapted LISP to create AutoLISP, preserving its functional philosophy while specifically tailoring it to CAD needs.

Key Features

Parentheses-Based Syntax

AutoLISP uses prefix notation where operators precede their operands, all enclosed in parentheses:

(+ 5 3)  ; Addition: 5 + 3 = 8
(* 2 4)  ; Multiplication: 2 × 4 = 8

List Processing

Like its LISP ancestor, AutoLISP excels at list manipulation, which is particularly useful for handling coordinates and object properties:

(setq point1 '(10.0 20.0 0.0))  ; Defines a 3D point

Native AutoCAD Integration

AutoLISP can directly interact with AutoCAD objects, access the drawing database, and use all software commands.

Interactive REPL Mode

The AutoCAD command line functions as a REPL (Read-Eval-Print Loop), similar to Python. This makes it very easy to test AutoLISP code directly from the AutoCAD interface. For example, you can simply type in the command line:

(alert "Hello")

This command will immediately display a dialog box with the message "Hello", enabling quick learning and prototyping.

Practical Applications

Automating Repetitive Tasks

• Automatic creation of standardized blocks
• Bill of materials generation
• Automatic area and volume calculations
• Batch updating of object properties

Interface Customization

• Creating new commands
• Developing custom dialog boxes
• Modifying menus and toolbars

External Data Integration

• Import/export to databases
• Reading Excel or CSV files
• Automated report generation

Advantages of AutoLISP

Accessibility

AutoLISP is relatively easy to learn for AutoCAD users, even without prior programming experience. Its simple syntax and extensive documentation facilitate learning.

Seamless Integration

Being built directly into AutoCAD, AutoLISP requires no additional installation or configuration. Programs can be loaded and executed directly from the AutoCAD interface.

Flexibility

The language allows creating custom solutions tailored to the specific needs of each user or company.

Active Community

A large community of users shares routines, tips, and solutions, facilitating learning and development.

Modern Evolution

Visual LISP (VLISP)

Autodesk introduced Visual LISP and its integrated development environment (VLIDE) which offers:

• A code editor with syntax highlighting
• An integrated debugger
• Automatic formatting tools
• An improved graphical interface

Since AutoCAD 2021, Autodesk offers an alternative to VLIDE: you can now use VS Code with an extension called AutoCAD AutoLISP Extension. Note that you cannot compile to fas or vlx formats; you still need to use VLIDE for that.

Modern Alternatives

Although AutoLISP remains popular, Autodesk also offers:

• VBA (Visual Basic for Applications): The advantage of this technology is that it's developed by Microsoft and is found in many applications like Microsoft Office or SolidWorks. However, it is now obsolete and no longer being developed. Furthermore, it is no longer installed by default with AutoCAD; it must be downloaded separately.
• .NET API: For developing robust applications in C#
• ObjectARX: For those who master C++ and want maximum performance

Limitations

Performance

As an interpreted language, AutoLISP can be slower than compiled languages for very intensive tasks.

Limited Portability

AutoLISP programs are specifically designed for AutoCAD and are not portable to other applications. However, they can often be used on AutoCAD clones such as DraftSight, BricsCAD, ZWCAD, GstarCAD, etc.

Technological Evolution

Although still supported, AutoLISP no longer evolves as much as more recent technologies offered by Autodesk. The list of latest changes can be found here

Limited User Interface Development Options

If you need to display data or create input forms, your choice will be limited to DCL (Dialog Control Library) technology, which is very basic and difficult to use, or OpenDCL which is also limited. Whereas in .NET for example, you can use WPF or WinForms which are much more powerful and flexible.

Practical Example

Here is a simple example of an AutoLISP routine that draws a rectangle:

(defun c:rectangle ()
  (setq pt1 (getpoint "\nStart point: "))
  (setq pt2 (getpoint pt1 "\nOpposite point: "))
  (setq pt3 (list (car pt2) (cadr pt1)))
  (setq pt4 (list (car pt1) (cadr pt2)))
  (command "LINE" pt1 pt3 pt2 pt4 "C")
  (princ)
)

This routine creates a new command called "RECTANGLE" that prompts the user for two points and automatically draws a rectangle.

Conclusion

AutoLISP remains a powerful and accessible tool for customizing and automating AutoCAD. Although more modern alternatives exist, its ease of learning and native integration make it a preferred choice for many AutoCAD users looking to improve their productivity. Whether for automating repetitive tasks or creating custom solutions, AutoLISP continues to play an important role in the AutoCAD ecosystem.

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