Two Eiffel Implementations
The two packages reviewed, ISE Eiffel-3 from Interactive Software Engineering (ISE), of Santa Barbara, California, and TowerEiffel from Tower Technology, of Austin, Texas, have much in common, including:
A short “Ace” file that describes the makeup of a system of classes comprising a program and that contains options to the compiler, most critically, the name of the root class and its creation procedure, and the class directories. Based on the Ace file, the compiler handles all dependency analysis itself.
A command line interface (not evaluated in this review). The graphical interfaces are nice, but not absolutely needed, and you can get around them if you find they are getting in your way.
Between 50KB and 100KB of static runtime binary libraries. Both ISE and Tower Technology plan to offer shared libraries in the ELF binary format when ELF stabilizes.
Eiffel class libraries are delivered in source or sometimes encrypted source form, with one file per class. Lots of classes are present in such a library, offering things such as linked lists, trees, file I/O, iterators, classes for object persistence and transmission, and much more.
Except for the kernel library, which furnishes hooks to the operating system and the runtime binary library, class libraries are planned to be portable across compilers. With the adoption of PELKS, the Proposed Eiffel Kernel Library Standard, all vendors now move toward a common kernel library interface supporting their other class libraries.
The Tower development environment is tailored to lemacs or its successor, xemacs. Neither is included in the distribution, but these editors are are commonly available from ftp sites and CD-ROMs. Look for lemacs-19.10 or xemacs-19.11. You can also use emacs, though the fit is less precise.
Tower is working on a non-emacs integrated development environment, to be in beta test by press time.
Installation was smooth, except for a little difficulty in the license setup. After some exchange of e-mail, a working license code was installed and TowerEiffel was up and running.
Program edit, class browsing, compilation, and debug are initiated from lemacs pull-down menu selections. A nice touch is the “Send performance report to Tower” menu item which e-mails a bug report. I mailed some, and got immediate responses.
The “Browse” menu item gives you library browsing capability, as well as allowing you to work with your own classes. Some very useful views were missing from the menu. Tower agreed, and had already implemented the most difficult of these. More choices will soon be available.
With all optimizations enabled, a small test application compiled from scratch in about one minute. The resulting binary used about 77KB of code space. A rough breakdown of this showed most of the code coming from the runtime library.
With all assertion checking on and no compiler optimizations, the binary file from compiling this application occupied about a megabyte. It still took one minute to compile from scratch.
Compiler errors list to a window, with explanations and references to Eiffel: The Language. If you click on the errors, the related program text appears in another window.
The Tower debugger, egdb, adapted from GNU gdb, is a command-line symbolic debugger. Xemacs or xegdb provide graphical front ends. Breakpoints may be set at any reasonable line of the Eiffel source code. When execution encounters a breakpoint the corresponding program text appears in a window. You can single-step one Eiffel statement at a time, and the cursor in the display window steps to the statement executed. When execution enters C code functions, egdb becomes a C source code debugger. All the other amenities familiar to gdb users are present.
There were a few mysteries about how to display the contents of some objects. Setting some breakpoints was also obscure. Other than that, egdb was straightforward. Source code awareness was good, and the ability to switch over to C mode was also nice, as time-critical or platform dependent parts of Eiffel systems are often implemented in C.
The TowerEiffel tools are rich in run-time options, not all accommodated in the menus. In particular, report generating tools, such as eshort, can produce output in text, LaTeX, plain roff, manpage roff, or LaTeX, or Rich Text Format for use in Word or NeXT. The options are well documented in man pages.
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