Unlike the original, MacTierra aims to present the user with a highly interactive interface so that simulations can be studied as they are running, saved to a file and restarted later, and the activities of the creatures within them closely monitored.
This Macintosh version of Tierra implements all of the features of the original version, as described in Ray (1991), and you are referred to this for details of how Tierra works. However, the long-term dynamics of the system do seem to be fairly sensitive to the details of the implementation, and it is probable that this system does not exactly replicate the results of the original, through small differences in the implemented architecture. It is yet to be determined how important these differences are.
MacTierra was implemented from scratch for a number of reasons. First, when I first read about the Tierra system (which instantiated a vague idea I had harboured for several years) I did not have access to the source code, nor experience in C. Secondly, MacTierra started as an excercise in Object Pascal programming (yes, most of the code is still Object Pascal!). Thirdly, I hoped the verify the results of the original Tierra by implementing a version in a different programming language, on a different platform. Finally, I wished for a version that was as easy to use as a drawing program, making use of innovate features of the Mac user interface (like Drag & Drop), and enabling interesting experiments to be performed quickly and easily. That goal has now been achieved.
Source code for the current version of Tom Ray's Tierra, which can be complied to run under DOS and UNIX, is available here.
See the Tierra publications list for details of more literature about the system.
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