Logo is a computer programming language that was initially intended to encourage children to learn about computers by creating shapes that are drawn by moving a turtle around a computer screen. Although the logo environment focuses on graphics and the graphical interface, it is also a powerful programming language.
NXLogo was designed at Colorado School of Mines during a six week summer field session for undergraduate students. We, Gary Desrochers and Sean Kerstiens, undertook the task of creating a working logo interface for the Next by the end of the course. The original logo interface had to be modified and a NeXT interface had to be added. The result of these efforts is NXLogo. Currently, the version is 1.0, as seen in the info panel of the application.
In general, most of the regular logo commands work for NXLogo. A few exceptions and changes are listed below. At the end of this file, a complete list of commands is given.
There are some parsing differences between logo and NXLogo. To begin with, a left bracket ([) must be closed on the same line as it is opened. This can be seen using a print statement. Here is a correct statement:
print [Hello. How are you?]
Also, there are no multi-line commands. This feature could not be added in the time period that was provided. It a useful feature that could be added in the future. There are also a couple new ways to enter a <to> procedure. To define a procedure from within the NXLogo application type:
to <procedurename> <:variable(s)> | <procedure must be on one line>
Another way to make a procedure is to create a file using a text editor. (Once you have defined a procedure from within Logo, this is the only way to make changes to that procedure. Unless you want to erase it and then redefine it.):
to <procedurename> <:variable(s)>
<procedure in as many lines as you want
end
In version 1.0 of NXLogo the procedure has to start on the first line of the file for NXLogo to recognize it properly. Once you have made the file in the editor, the file must be saved as <procedurename>.lg in your working logo directory.
The working logo directory is another important point. There is a system library (included in the package as NXLogoLibrary) that can hold any of the global (everyone can use) logo procedures. NXLogo will search your home directory first before it goes and does the main library search. If it doesn't find the procedure in there, then it will tell you it doesn't know how to do that procedure name. This means that you can redefine a system defined procedure by making your own. You can change your personal working directory to anything you like with a NeXT unix command called dread. To do this simply perform a dread NXLogo NXLogoLib <pathname terminated with a />. Here is and example:
It is very important to include the slash (/) after the last directory name, otherwise NXLogo will not recognize the directory. The system library can also be changed with this command. There is a help directory (included in the package as NXLogoLibrary/help) and this can be changed with the dread also. These two can be changed with:
In the future this will also be made into a preferences menu for the system administrator so that he will not have to relink the whole program to change the directory. This would not be too hard but was not done due to time limitations.
Another way to personalize your environment is to drag the NXLogo
program's icon to the right side of the screen under the Next Cube and then every .logo file will show up as a turtle. In the future, when a .logo file is double clicked NXLogo will load that one file and display it in the NXLogoprogram. Currently it only loads up logo. (Sorry folks, maybe in another version!)
