Permission to copy The CAD Academy

Transcription

1 Use LISP to Program in A+CAD Permission to copy The CAD Academy

2 We are going to create a small program in LISP, a language used in artificial intelligent programs, to interact with our CAD program A+CAD. LISP is a LIST processor or works with lists. Custom programming gives users the power to make everyday tasks easier and to create applications. Load A+CAD and make sure you are in the drawing editor. Your screen should looks something like this. Double click on the SNAP and GRID at the bottom right of the screen to turn on the GRID and the SNAP (they are grey right now and will turn black when turned on). Find the ZOOM EXTENTS icon or zoom extents to home up the screen.

3 Page 2 Draw a 4 x 4 square. At the command line type in ID and press enter Select the upper LEFT corner on the square. You will receive the X Y and Z points of that corner. They may be different than shown. Use yours and write them down on a piece of paper. This would be 3,7.0 Using the ID command get the X Y and Z of each corner and write them down and then ERASE or DELETE the square.

4 Page - 3 We will use the POINT information we just wrote down to create our first program. A+CAD is actually a DATABASE and you can create on the screen with a mouse or by directly talking to the database using LISP. LISP is a small programming language, but very powerful. To program you need a TEXT EDITOR and we are going to use one supplied in WINDOWS. Programs have trouble with word processors because they add characters that they cannot read. Type in SHELL and then EDIT to bring up a generic TEXT EDITOR. Normally a programmer designs and plans the program by writing it out in English using pseudocode. We are going to just dive right in because this one is short and simple.

5 Page 4 First comes the REMARKS for the program. In this section you normally NAME the PROGRAM, NAME the AUTHOR and TELL OTHERS what the program will do. A REMARK is always started with a semi-colon ; The program disregards this information, but this information identifies the program and what it will do. Next we need to DEFINE the program and give it NAME. DEFUN is a Lisp FUNCTION. All LISP statements have MATCHING parenthesis, but in this instance we leave one open so that the program will EVALUATE until it finds the missing parenthesis. ALWAYS make sure you don t define a program name that is the same name as a command like: line, arc, circle, etc. I try to keep the name short to make it easy to use. Click on the A+CAD drawing screen.

6 Page - 5 The command line can be used to CHECK out LISP statements or used to debug the program (as they call it in programming). We are going to play with a statement that will make our first point. SETQ in LISP sets a shortened name or VARIABLE to represent data. So at the command line we are going to type in: (SETQ P1 (3 7 0)) What that statement is saying is P1 (short for point 1) stands for Notice the matching parenthesis. Also notice the apostrophe. The apostrophe tells the program that the following is a list of

7 Page 6 information that belongs together. In the case it represents an X Y Z point on the screen. When you press ENTER the program will ANSWER back (3 7 0) telling us it received the information. Type in!p1 at the command line. By place an exclamation point in front of the VARIABLE it will tell you what is stored in it. This is useful information for programming. At the command line type in C and enter for CIRCLE. When prompted for the CENTER POINT don t PICK anything, but TYPE IN!P1 at the command line and press ENTER. Using this VARIABLE we are able to locate the exact point that is stored in P1 on the screen. Tab back to your program. Use the point information YOU WROTE down for these points. After putting in your points we need to draw the square. You can use ANY A+CAD command in LISP

8 Page 7 as long as you put QUOTES around it. So we will be drawing a line from POINT 1 to POINT 2 to POINT 3 and then POINT 4, but in A+CAD we would still need to CLOSE it so we add CLOSE at the end. The FINAL line is the CLOSING parenthesis that we left out at the beginning. When you get done with the program we need to SAVE the program before we can RUN the program. USING the SAVEAS from the FILE pull down make sure you save the file in a location you can find and also to put an EXTENSION of.lsp on it to signify that it is a LISP program. SAVE as SQ.LSP This is where the FUN starts. Let s see of our first program works.

9 Page 8 You type in (load c:/directory/name of file ) in the command line as shown at right and press ENTER. The reason we use the opposite slash is the backslash means divide in LISP. It should answer back with the DEFUN or DEFINED name of the LISP ROUTINE. In this case SQ. If it does not work or you get an error go back and make sure you named the file correctly and that you know where it is located. Also, bring it up to edit and see if you left out a quote or a parenthesis or spelled something incorrectly. If you get the SQ back. Type in SQ at the command line and watch your program run. Congratulations on your first program. Be sure and SAVE the file as we will add more information to the program in another lesson. Lesson is complete