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Subject: Icon Programming Language FAQ
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Frequently Asked Questions About The Icon Programming Language

Last updated: February 16, 1996

This FAQ answers various questions about the Icon programming language, ranging
from what it is to how you can get it. The master copy of this FAQ is the Web
page http://www.cs.arizona.edu/icon/www/faq.html. Other on-line documentation
is available via the main Icon page at http://www.cs.arizona.edu/icon/www/.

This FAQ is written by Ralph Griswold and Gregg Townsend, with help from Cliff
Hathaway, Clint Jeffery, and Bob Alexander.

   * 1. What is Icon?
   * 2. What is Icon good for?
   * 3. Where did Icon come from?
   * 4. What does "Icon" stand for?
   * 5. On what computers does Icon run?
   * 6. Who did all these implementations?
   * 7. Are there other implementations in the works?
   * 8. What about different versions of Icon?
   * 9. Which implementations of Icon have graphics/window capabilities?
   * 10. Where can I get Icon?
   * 11. Where can I get documentation about Icon?
   * 12. How do I get started with Icon?
   * 13. What is the Icon Project?
   * 14. Where can I find examples of Icon programs?
   * 15. What is Idol?
   * 16. How often is material in Icon's FTP area updated?
   * 17. How do I stay up to date with what's going on with Icon?
   * 18. Is there a users' group for Icon?
   * 19. How do I get technical support?
   * 20. Should I use the Icon interpreter or compiler?
   * 21. What do I need to run the interpreter?
   * 22. What do I need to run the compiler?
   * 23. Can I build my own implementation of Icon for a new platform?

-------------------------------------------------------------------------------

1. What is Icon?

Icon is a very high level general-purpose programming language with extensive
features for processing strings (text) and data structures. Icon is an
imperative, procedural language with a syntax that is reminiscent of C and
Pascal, but its semantics are at a much higher level than those languages.

Icon has a novel expression-evaluation mechanism that integrates goal-directed
evaluation and backtracking with conventional control structures. It has a
string scanning facility for pattern matching that avoids the tedious details
usually associated with analyzing strings. Icon's built-in data structures
include sets and tables with associative lookup, lists that can be used as
vectors or stacks and queues, and records.

Icon is a strongly, though not statically, typed language. It provides
transparent automatic type conversion. For example, if an integer is used in an
operation that requires a string, the integer is automatically converted to a
string.

Several implementations of Icon have high-level graphics facilities with an
easily programmed window interface.

Icon manages storage automatically. Objects are created as needed during
program execution and space is reclaimed by garbage collection as needed. The
sizes of strings and data structures are limited only by the amount of
available memory.

2. What is Icon good for?

As a general-purpose programming language with a large computational
repertoire, Icon can be used for most programming tasks. It's at its best when
used as a prototyping tool, for processing text, and when ease of programming
is needed for experimental and research applications.

Paradoxically, Icon is used most often for short, one-shot tasks and for very
complex applications.

Icon is designed to make programming easy; it emphasizes the value of
programmer's time and the importance of getting programs to work quickly. This
explains its usefulness for prototyping as well as the apparent paradox of
applicability to simple and complex applications.

3. Where did Icon come from?

Icon is the latest in a series of high-level programming languages designed to
facilitate programming tasks involving strings and structures. The original
language, SNOBOL, was developed at Bell Telephone Laboratories in the early
60s. SNOBOL evolved into SNOBOL4, which is still in use. Subsequent languages
were developed at The University of Arizona with support from the National
Science Foundation.

Incidentally, Icon bears little physical resemblance to SNOBOL4, although it
has similar objectives and many similar capabilities.

4. What does "Icon" stand for?

The name Icon (which is not spelled ICON) is not an acronym nor does it stand
for anything in particular, although the word "iconoclastic" was mentioned at
the time the name was chosen. The name predates the now common use of "icon" to
refer to small images used in graphical user interfaces. This latter usage
sometimes causes persons to think mistakenly that Icon is designed to create or
manipulate icons. There's not much that can be done about this.

5. On what computers does Icon run?

The implementation of Icon is highly portable. Version 9 runs on UNIX, MS-DOS,
Macintosh/MPW, VAX/VMS, and the Acorn Archimedes. There are older versions for
the Amiga, the Atari ST, IBM CMS and MVS, the Macintosh, and OS/2.

Icon programs also are highly portable. Most Icon programs can run on any
platform that supports Icon.

6. Who did all these implementations?

The original implementation of Icon for UNIX was done at The University of
Arizona. Most of the other implementations originally were done by volunteers
scattered around the world.

It's worth noting that all implementations of Icon are based on the same source
code, which is written in C. This contributes to the portability of Icon
itself, as well as to the portability of programs written in Icon.

7. Are there other implementations in the works?

Work is constantly underway on implementations of Icon for new platforms.
Present projects include Microsoft Windows, Windows NT, and a new Macintosh
implementation.

8. What about different versions of Icon?

Icon has evolved through a series of versions with improved and extended
capabilities. The latest major version number is 9. This version includes
recent changes and additions, notably in the graphics area, and runs on UNIX,
MS-DOS, Macintosh/MPW, VAX/VMS, and Acorn Archimedes. Other implementations
presently are at Version 8. Almost all programs that run under Version 8 and
that do not use graphics will run under Version 9.

9. Which implementations of Icon have graphics/window capabilities?

Icon's graphics facilities presently are supported on UNIX and VAX/VMS. The
Windows NT and Microsoft Windows implementations that support Icon's graphics
facilities are in beta testing. A Macintosh implementation to support graphics
also is in the works.

10. Where can I get Icon?

Icon is available via anonymous FTP and on the Web. For FTP, use

     ftp.cs.arizona.edu

and cd /icon.

For the Web, use

     http://www.cs.arizona.edu/icon/www/

and check out the links there.

For FTP, the directory /icon/binaries contains executable versions of Icon for
several systems, including several popular UNIX platforms. The directory
/icon/packages contains source code, test programs, related material, and, most
cases, executable binaries as well. All directories have README files with
additional information.

Icon also is available on diskettes for prices ranging from $15 to $25.
Contact:

     Icon Project
     Department of Computer Science
     The University of Arizona
     P.O. Box 210077
     Tucson, AZ 85721-0077

     520-621-6613 (voice)
     520-621-4246 (fax)

     [e-mail]

Purchases can be made by credit card (MasterCard or Visa), postal money order,
or check drawn on a bank with a branch in the United States and made payable to
The University of Arizona.

Icon is available on CD-ROM from Prime Time Freeware (http://www.ptf.com/,
408-433-9662). Contact them for details.

11. Where can I get documentation about Icon?

The definitive work on Icon is the book

     The Icon Programming Language, Griswold and Griswold, second edition,
     Prentice Hall, 1990, 368 pages, ISBN 0-13-447889-4.

This book is a complete description and reference manual for Version 8 of Icon.
A technical report describes changes since that version.

There also is a book on the implementation of Icon:

     The Implementation of the Icon Programming Language, Griswold and
     Griswold, Princeton University Press, 1986, 336 pages, ISBN
     0-691-08431-9.

This book describes the implementation as of Version 6 of Icon. Although the
implementation has changed considerably since then, the basic structure is the
same. Technical reports describing recent implementation changes are included
with copies of the book purchased from the Icon Project.

These books are available from the Icon Project.

Additional documentation is available via FTP in /icon/doc. Notable documents
are:

   * IPD266: An Overview of Icon (text, PostScript, PDF)
   * IPD268: Graphics/window facilities (PostScript, PDF)
   * IPD267: Version 9.1 of Icon (text, PostScript, PDF)

There are manual pages for Unix systems, and more documentation under the Icon
web page, but there is no complete on-line documentation.

The Icon Newsletter, which includes topical material about Icon and a list of
material available from the Icon Project, is published three times a year and
is available on the Web. There is a subscription fee for an on-going
subscription by postal mail. The Icon Analyst, a technically-oriented
newsletter that features articles about programming, is published six times a
year. There is a subscription fee for the Analyst. A sample copy is available
on the Web.

All back issues of both newsletters are available for purchase.

12. How do I get started with Icon?

If you're running under Unix, check first in the /icon/binaries/unix FTP
directory to see if there is a "starter kit" for your platform. Starter kits
include executables, documentation, and other material.

Otherwise, go to the /icon/packages directory and get the appropriate package.
Packages include documentation and other material; see the README file in that
directory for more details. There is a Unix package for platforms that lack
starter kits.

If the non-Unix package you pick up does not contain executable files, check
/icon/binaries. You also may want to get the overview of Icon:
/icon/doc/ipd266.doc or ipd266.ps.Z. You'll find pointers to other documents of
interest in the package you pick up.

13. What is the Icon Project?

The Icon Project is a name used by the group that develops, implements,
distributes, and supports the Icon programming language.

The Icon Project is not commercial organization. It derives support from The
University of Arizona, revenue from the sale of program material and
documentation, and user contributions.

14. Where can I find examples of Icon programs?

There is a large program library for Icon. It is an excellent resource for both
new and experienced programmers. The library contains numerous examples of how
to do things with Icon. The library also provides many useful applications, as
well as hundreds of procedures that supplement Icon's built-in repertoire.

The library, like other Icon material, is available via FTP in /icon/library
and on diskettes from the Icon Project.

15. What is Idol?

Idol is an object-oriented extension to Icon that provides concepts such as
classes and multiple inheritance. Idol is written in Idol and is distributed as
part of the Icon program library. Idol runs on almost all of the platforms that
support Icon.

Additional Idol information is available from Clint Jeffery,

     [e-mail].

16. How often is material in Icon's FTP area updated?

New material is added when it's available. Established implementations usually
are updated only when there's a major new release. This typically is every year
or two. The Icon program library is updated on a similar schedule.

17. How do I stay up to date with what's going on with Icon?

The best way to find out about developments related to Icon is to read the Icon
Newsletter.

You can stay up to date on the source code, which is changed much more
frequently than the version on FTP is updated, by subscribing to the source
update service, which provides a new version about twice a year.

There also is a subscription service for updates to the Icon program library,
which provides new material about twice a year.

There is on-line information about subscribing to these services.

18. Is there a users' group for Icon?

There is no official Icon users' group. The Icon Project maintains an
electronic mailing list,

     [e-mail].

Mail sent to this address is forwarded to subscribers. To subscribe (or
unsubscribe), send a message to

     [e-mail].

There is a gateway between icon-group and comp.lang.icon, an unmoderated
newsgroup for discussing issues related to Icon. The gateway, which exchanges
messages between the two systems, is imperfect and not under the control of the
Icon Project.

The newsgroup generally provides faster response than the mailing list, is less
intrusive, but sometimes suffers from inappropriate postings. The Icon Project
usually sends messages of interest to the Icon community to icon-group.

19. How do I get technical support?

The Icon Project is not a commercial organization, and its capacity for
providing technical support is limited. Please use the appropriate resource
when you need assistance:

Ordering Icon Material

mail:   Icon Project
        Department of Computer Science
        The University of Arizona
        P.O. Box 210077
        Tucson, Arizona 85721-0077
        U.S.A.

fax:    [phone]
voice:  [phone]
e-mail: [e-mail]

Getting On-Line Information and Material

web:    http://www.cs.arizona.edu/icon/www/
ftp:    ftp.cs.arizona.edu (cd /icon)
e-mail: [e-mail]

Send a message consisting of the word help.

Assistance with Installing Icon

e-mail: [e-mail]

Bug Reports

e-mail: [e-mail]
fax:    [phone]

Assistance with Programming Problems

e-mail: [e-mail]
news:   comp.lang.icon

Uploading Files

ftp:    ftp.cs.arizona.edu (cd /incoming)

After uploading, send e-mail to [e-mail].

20. Should I use the Icon interpreter or compiler?

As the question indicates, there are two forms of the implementation of Icon,
an interpreter and a compiler. The interpreter gets a program into execution
quickly and is recommended for program development, debugging, and most
production situations. The compiler produces code that executes somewhat faster
than interpreted code (a factor of 2 or 3 is typical), but the compiler
requires a large amount of resources and is very slow in producing executable
code. It also requires additional time and effort at installation time. The
compiler is recommended only for small programs where execution speed is the
paramount concern.

21. What do I need to run the interpreter?

The Icon interpreter will run on most computers. Under MS-DOS, the Icon
interpreter needs 500 KB of application RAM to work well.

22. What do I need to run the compiler?

The Icon compiler is another matter. It requires a C compiler, a fast CPU for
tolerable compilation times, a considerable amount of disk space, and a lot of
memory -- at least several megabytes.

The Icon compiler generates C code, which must then be compiled to produce an
executable program. The flexibility that Icon provides to programmers makes
compilation technically difficult and the process requires a large amount of
memory. The C code it produces is voluminous and stresses the most robust C
compilers.

Generally speaking, the Icon compiler is practical for platforms in the
workstation class but not for personal computers.

23. Can I build my own implementation of Icon for a new platform?

As mentioned above, Icon is written in C and the source code is available. The
existing implementations are testament to its portability. (A small amount of
assembly-language code is required for a context switch, but this is only
needed for an optional feature -- co-expressions -- that can be disabled
without affecting most of Icon.)

New ports involve platform-specific configuration parameters and, in some
cases, platform-specific code. The feasibility of a new port and the amount of
work it may take depends on the platform -- its architecture, its C compiler,
and its environment.

Ports to new Unix platforms generally are easy, although novel architectures
may present problems. Ports to new operating systems generally are more
difficult, especially if Icon's graphics facilities are implemented.

The Icon Project provides what help it can with new ports. In return, it asks
that code related to the port to be returned to the Icon Project for inclusion
in future versions of the source code for Icon. This makes the new port
available to others as well as to the porter when Icon is updated.