In addition to providing power and compactness of representation, having an interpreted programming language at the network and graphics layer of a computer system provides a very neat solution to problems of transportability and machine independence, since many of the decisions are delayed until run-time. One important concept in object-oriented programming in general is to keep the interface between objects clean enough that there are not any problems when you hook them together. This is especially important where you have to write programs at the places where objects meet. It is important for you, the reader and programmer, to understand PostScript well enough to create programs that behave well in the nested, shared, cut-and-pasted environments that exist today.

DATA STRUCTURES AND ALGORITHMS

The classic view of a computer program is a synthesis of data structures and algorithms. Books often have titles that contain these two words, and every program probably has one or the other in it somewhere. If you use PostScript to describe pages and to drive laser printers, your need for real data storage and computation should be minimal. However, if you use PostScript in a windowing environment to arbitrate input events from the keyboard (as an extreme example), you will definitely need to create data structures and implement some potentially difficult algorithms.

CONCLUDING THOUGHTS

The next several chapters help you build some solid approaches to PostScript data structures and help you master the language elements thoroughly so that you will feel comfortable implementing your favorite algorithms. In particular, the data types unique to PostScript are explored (dictionaries and names) as well as traditional data types such as strings, arrays, and numbers. Other chapters are devoted entirely to seemingly simple things like the ifelse operator or looping. However, since PostScript was not originally designed for heavy programming, these traditional programming techniques have never been thoroughly addressed. And you simply can’t write a serious PostScript program without using ifelse or writing a procedure or two.

EXERCISES

Each chapter in this book comes with some exercises at the end of it, to help you to test your understanding of the concepts presented. Since this first chapter has taken a philosophical overview of PostScript as a programming language, the exercises are more like essay questions than problems.

1.Why do you want to write a PostScript program? (This is a serious question, and one which should be given some thought; reflection on why may provide you with good horse sense throughout your programming experience.)

2.Why is PostScript a “backwards” language, in which the operators come after the operands?

3.Why is PostScript an interpreted language?

4.Why is it silly to write fractal programs in PostScript?