COMPARISON OF LANGUAGE MECHANISMS

One of the first skills a programmer develops is the ability to

conceptualize the procedures that will be needed for a program to be

implemented effectively. These procedures are designed by deciding what

data are needed, how that data ought to be passed through the control

sequence of the program, and how the naming of the procedures will

contribute to the readability and flow of the program. Procedures should

not be too big and complex, nor too small and inefficient.

There is a major difference between PostScript and C that makes program

design completely different. In C, you basically have no built-in language

elements. There are a few control structures, loop constructs, some

input/output operations, and the inherent procedure call mechanism, but

there aren’t a lot of individual operators as there are in PostScript. In a

sense, the entire program design is based on the implementation of

procedures or modules.

In PostScript program design, almost the opposite is true. There are well

over 300 individual PostScript operators. Very efficient, well-designed

programs can be constructed without ever writing a single procedure, just

by using the built-in operators. Then, when the functionality of the

program fully emerges, the ability to define procedures can help you to

organize the code or to make it more efficient, but usually it is not a good

approach to begin by designing the procedures themselves, since the work

is ultimately carried out by the individual operators anyway.

TIP

A PostScript procedure is simply a set of operations that are grouped

together and that can be invoked by a single instruction. They do not

replace the individual operations, they merely provide another way to

cause them to be executed. The principle advantages to defining

procedures is to collect sequences of operations that may be performed

repeatedly.

Furthermore, the operand stack is the communication area between

procedures; it is the only place where you can pass data between

procedures. But, since this is also the way data are passed to individual

PostScript operators, the distinction between a sequence of PostScript

Chapter 2: POSTSCRIPT IS NOT LIKE C

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