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Pascal ARRIVES

By Chris Derossi

Well, after waiting and waiting and waiting, Macintosh Pascal has finally arrived, and with its arrival, Mac users now have a serious high-level language for programming on the Macintosh. This column will help the users of Macintosh Pascal both to learn about Mac Pascal, and to learn how the wonderous abilities of the Mac ROM can tie into Mac Pascal for creating powerful and useful programs.

For this opening column, we’ll be taking a general look at Pascal, and we’ll see how you can get started right away learning how to use your Pascal to the fullest. Let us start out by examining the contents of your Pascal package.

The documentation is in three separate parts, with each section contained in its own little booklet. The first, and smallest book contains the standard instructions for using the normal Macintosh User Interfaces, to which Mac Pascal conforms. For experienced users of the Mac, this book will be of very little help; you already know all about clicking, dragging, and editing with the mouse. For the less experienced user, this book will teach you what you need to know in order to get started with Pascal right away.

The most important part of this book is the section which describes the use of the Observe and Instant windows. This is the only explanantion of these windows found in the documentation. As we get further into Pascal, the importance of these windows will grow.

The booklet titled “Pascal Reference Manual” is an important tool for beginners and experienced programmers alike. Although it is not a tutorial, it does contain the entire syntax specification for Mac Pascal. Its primary use is as a look-up reference. New Pascal programmers may wish to go through the manual to get a general feel for the language, but as I’ll discuss shortly, more can be learned by studying the example programs supplied with Mac Pascal.

The final book, “Macintosh Technical Appendix”, is probably the most useful manual included. This manual describes the differences between Mac Pascal and both Lisa Pascal and ANS Pascal. In addition, this book has detailed information on two important areas of Mac Pascal: QuickDraw and SANE. Both of these will be covered in detail in further issues of MacTech.

Unfortunately, none of the documentation included with your Mac Pascal goes into any depth in the area of the Mac ROM, except for the QuickDraw section which is really more concerned with mathematical concepts. To learn about the language, and find out its limitations and its capabilities, we will be exploring a large variety of topics in this column. To begin with, however, a good source of information can be found in the example programs contained on your Pascal disk.

The Pascal disk contains a number of interesting programs that demonstrate some features of Mac Pascal. As you’ll notice, most of the examples contain graphics, but some of them display the ability of Mac Pascal to do things like change window size, modify the cursor, interact with the mouse and the keyboard, and perform file I/O. Indeed, Mac Pascal has a wide range of abilities. Although many of the procedures and functions used in the examples are not clear, browsing though the included examples is a good way to get a feel for the power of Mac Pascal, and an idea of the range of functions available.

The other item that is included with your Mac Pascal disk is a second Mac Pascal disk. This is an exact copy for backup purposes. The backup disk is included because Mac Pascal is copy protected. The diskette cannot be copied, and the Pascal file cannot be moved to any other disks, including hard disk drives. The files, on the other hand, can be moved and should be copied.

Now that we’ve examined the things that are contained in your Mac Pascal package, let’s say just a little bit about the interpreter itself. Before Mac Pascal, Pascal programs were compiled. That is, the Pascal program was written into a text editor. Then, the Pascal compiler read the program text and converted it to a form that the computer could execute. The machine executable version was called object code, and the original text version was called source code.

If a program was to be modified, the text of the program had to be changed, and then the whole thing had to be compiled again. This could take lots of valuable time. On the other hand, the object code, since it was usually directly executable by the computer, ran very quickly. Macintosh Pascal, however, is not compiled; Mac Pascal is interpreted.

When we say that Mac Pascal is interpreted, we mean that the program is enterred into a text editor which is part of the language interpreter. When the program is run, the interpreter reads the program and converts each line to an executable format. The individual lines are converted and run each time they are needed, and the converted lines are not kept available. This means that interpreted programs generally run slower than compiled programs. If the program is to be changed, though, it can be re-run immediately after modification. This decreases the amout of development time required .

In conclusion, Macintosh Pascal presents a useful and powerful programming environment for the Mac user. For the beginner, Pascal provides an excellent learning vessel, and for the experienced Mac user, Pascal provides a useable, structured interface to the internal magic of the Macintosh. This column will explore and enhance these qualities of Mac Pascal and will help you to better understand and take advantage of Mac Pascal.

program Benchmark;

{creative computing benchmark}

 type
  datetimerec = record
    year, month, day, hour, minute, second, dayofweek : integer
   end;

 var
  a, r, s : extended;
  i, n : integer;
  result1, result2 : extended;
  begintime : datetimerec;
  endtime : datetimerec;
  t1, t2 : longint;

begin   {of main program}

 gettime(begintime);
 for n := 1 to 100 do
  begin
    a := n;
   for i := 1 to 10 do
      begin
         a := sqrt(a);
         r := r + random
    end;
    for i := 1 to 10 do
      begin
        a := a * a;
         r := r + random
    end;
    s := s + a
  end;

 result1 := abs(1010 - s / 5);
 result2 := abs(1000 - r);
 gettime(endtime);
 t1 := begintime.hour * 3600 + begintime.minute * 60 +   begintime.second;
 t2 := endtime.hour * 3600 + endtime.minute * 60 +       endtime.second;
 writeln(‘time in seconds=’, t2 - t1);
 writeln(‘ accuracy=’, result1 : 20 : 18);
 writeln(‘ random=’, result2 : 20 : 18);

end.