Volume Number: 14 (1998)
Issue Number: 5
Column Tag: MacTech Online
by Jeff Clites online@mactech.com
Here's the deal: Scripting languages are becoming a big thing these days, and the Macintosh is by no means being left out in the cold. Scripting languages integrate with Java, complement Java, provide alternatives to Java, and stand on their own. We're going to use this month's issue on Java as a jumping-off point for learning about some lesser-known languages for the Mac.
Scripting languages are not newcomer replacements for AppleScript or Frontier. "Traditional" scripting languages (if there is such a thing) developed in the Unix world. Like AppleScript, they tend to stitch together pieces written in languages such as C and Pascal, but there is an important distinction: whereas AppleScript operates primarily on applications, these scripting languages operate primarily on data. They may rely on components (analogous to Scripting Additions, or OSAX), and they can be made to interface with AppleScript, but they are a different breed, grown up with a different focus in mind.
Scripting languages are usually interpreted, meaning that they run directly from human-readable programs, rather then first being compiled into machine-executable form. As a result, they require an interpreter to run -- the analog of the Java virtual machine. To an even greater extent than Java, this allows platform independence. For those who are not impressed by this, or who worry about execution speed, many scripting languages are developing compiled implementations.
To get started, check out the excellent article Choosing a Scripting Language on the SunWorld site, which does a great job of introducing the big players, Perl, Tcl, and Python, and of getting the reader excited about them. Then, check out Scripting: Higher Level Programming for the 21st Century, which explains in detail how and when scripting languages can be more powerful and convenient than system programming languages, like C++ or Java.
Perl (the Practical Extraction and Report Language) began as a language for manipulating text and extracting information from it, sporting such power features as built-in regular expression (a.k.a. grep) capabilities, and accordingly has become popular for writing CGI scripts to generate web pages on the fly. It is probably the most well-supported of the scripting languages on the Mac, with a CD and a forthcoming book from the Free Software Foundation, which hosts the MacPerl pages. Perl could be a nice teaching language -- the MacPerl book aims to serve as a guide for those learning Perl as their very first programming language, as well as introduce the language to experienced programmers. Don't let Perl's text-based roots put you off -- they are only one of its strengths. It is a large language with an emphasis on practicality and the motto "There's More Than One Way To Do It."
Tcl (the Tool Command Language) is being actively developed by Sun as a scripting companion to Java, complemented by Tk (the Tool Kit) which provides it with a GUI. Tcl is completely untyped -- "everything is a string." This may horrify long-time Pascal or C programmers, but it is a strength -- it gives Tcl a unique flexibility and an amazingly readable style. It follows Perl in its level of Mac support, as Sun has a separate page devoted to Tcl/Tk for the Mac. They even have a browser plugin which allows you to run Tcl scripts within web pages, complete with Tk interfaces. Of course, Tcl/Tk can readily be used in Java-free contexts, where it started. A great example is the popular shareware text editor Alpha, which uses Tcl as its internal scripting language, allowing users to customize Alpha by writing Tcl scripts. For instance, you can teach Alpha to syntax-color a new language; this is actually an excellent way to start experimenting with Tcl.
Python (named, yes, after Monty Python) in many ways sits at the intersection of scripting and system programming languages. It is dynamic and object-oriented -- the types of variable are not determined until the last possible moment during execution, and programmers still stinging from the demise of Apple's Dylan project will be happy to hear that as in Dylan, everything in Python is an object. It is well suited to metaprogramming, easily generating executable code on the fly. It is also said to excel at group projects: it's highly modular, scales well, and its syntax makes it easy for one programmer to read another's code. In almost all ways, Python is a small language, but it packs power -- it has exception-handling facilities and high-level data structures, and the latest release has added Perl-like regular expressions. There is even JPython, a Java-based interpreter. The Python Language Home Page is the place to start. Also be sure to check out the SunWorld article Getting started with Python, which serves as a nice introduction, and then visit the Python Compared to Other Languages page to gain some perspective.
Scripting languages generate enthusiasm, and for more than just their power. They all reflect the personalities of their inventors, all are still evolving, and all are free (including the source code). Spend and hour or two playing with one -- it will be a pleasant experience. As you do, check out the following personal pages of a few Mac scripting experts, where you will find powerful tools as well as useful examples.
This is an especially important month to visit our companion web pages at www.mactech.com/online/, where these links are supplemented by a wealth of other links about Perl, Tcl/Tk, and Python, as well as other programming resources.
