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diff --git a/doc/faq.txt b/doc/faq.txt index 91b4eb9..8538984 100644 --- a/doc/faq.txt +++ b/doc/faq.txt @@ -1,8 +1,7 @@ - Frequently Asked Questions about the Icon programming language www.cs.arizona.edu/icon/faq.htm - Last updated November 14, 2005 + Last updated April 12, 2010 Learning about Icon A1. What is Icon? @@ -23,7 +22,7 @@ C1. What is the Icon Project? C2. How often is the on-line material updated? C3. Where did Icon come from? - C4. Where is Icon going? + C4. Where is Icon going? Support D1. Is there a users' group for Icon? @@ -41,41 +40,43 @@ Learning about Icon A1. 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 with semantics at a much higher level. + 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 with semantics at a much higher + level. 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. + 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. + 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. + 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. + 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. A2. 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 especially - strong at building software tools, for processing text, and for experimental - and research applications. + repertoire, Icon can be used for most programming tasks. It's + especially strong at building software tools, for processing text, and + for experimental and research 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. - Consequently, Icon is used both for short, one-shot tasks and for very - complex applications. + programmer's time and the importance of getting programs to work + quickly. Consequently, Icon is used both for short, one-shot tasks and + for very complex applications. A3. What are Icon's distinguishing characteristics? @@ -85,7 +86,8 @@ Learning about Icon * Usually interpreted * Evolved from programming languages (vs. scripting languages) - * Procedural control flow plus generators and goal-directed evaluation + * Procedural control flow plus generators and goal-directed + evaluation * Values have types; variables are typeless, accept any value * Static scoping: global or (procedure) local @@ -97,14 +99,17 @@ Learning about Icon * Also has sets, tables, records (structs), reals (doubles), more * No second-class "primitive types" - * Not "object-oriented" (no classes, inheritance, or instance methods) + * Not "object-oriented" (no classes, inheritance, or instance + methods) * No exception catching - * No concurrency (no threads, monitors, semaphores, or synchronization) + * No concurrency (no threads, monitors, semaphores, or + synchronization) * Has co-expressions (coroutines) * Basic least-common-denominator system interface (a la ANSI C) - * Procedural graphics (event-driven paradigm available but not mandated) + * Procedural graphics (event-driven paradigm available but not + mandated) * Retained windows (programs are never called to repaint) * Simple GUI builder that can re-edit its generated code * Turtle graphics package @@ -113,15 +118,17 @@ Learning about Icon A4. What is the Icon program library? - The library is a collection of programs and procedures written in Icon. User - contributions are welcome and form a significant portion of the library. + The library is a collection of programs and procedures written in + Icon. User contributions form a significant portion of the library. - Library procedures effectively augment the built-in functions available to - an Icon program. A wide variety of procedures currently exists, and most - graphically-based programs are built around library procedures. + Library procedures effectively augment the built-in functions + available to an Icon program. A wide variety of procedures currently + exists, and most graphically-based programs are built around library + procedures. The core and graphics core modules are the most carefully + vetted. - The programs in the library range from simple demonstrations to handy tools - to complex graphical applications. + The programs in the library range from simple demonstrations to handy + tools to complex graphical applications. The library is a resource for both new and experienced programmers. In addition to their basic utility, its programs and procedures serve as @@ -138,32 +145,37 @@ Learning about Icon www.mitchellsoftwareengineering.com/icon * John Shipman's tutorial: www.nmt.edu/tcc/help/lang/icon + For the graphics facilities: + * The Icon Project Overview: + www.cs.arizona.edu/icon/ftp/doc/ipd281.pdf + A6. Where are some simple examples? - For some simple text-based programs, see any of those introductory documents - in the preceding question. For some simple graphics programs, see - www.cs.arizona.edu/icon/gb/progs/progs.htm. + For some simple text-based programs, see any of those introductory + documents in the preceding question. For some simple graphics + programs, see www.cs.arizona.edu/icon/gb/progs/progs.htm. - Many more examples, typically larger, are found in the Icon program library; - see the indexes of Basic Programs and Graphics Programs. + Many more examples, typically larger, are found in the Icon program + library; see the indexes of Basic Programs and Graphics Programs. A7. How about comprehensive documentation? - Two books define the Icon language. The core language is covered in The Icon - Programming Language (third edition), by Griswold and Griswold. Graphics - facilities are described in Graphics Programming in Icon by Griswold, - Jeffery, and Townsend. These books contain both tutorial and reference - material. + Two books define the Icon language. The core language is covered in + The Icon Programming Language (third edition), by Griswold and + Griswold. Graphics facilities are described in Graphics Programming in + Icon by Griswold, Jeffery, and Townsend. These books contain both + tutorial and reference material. - Icon's internals are detailed in The Implementation of the Icon Programming - Language by Griswold and Griswold. Although considerable changes have - occurred since Version 6, described in the book, the basic structure of Icon - remains the same. Two technical reports, IPD112 and IPD239, describe - subsequent changes. + Icon's internals are detailed in The Implementation of the Icon + Programming Language by Griswold and Griswold. Although considerable + changes have occurred since Version 6, described in the book, the + basic structure of Icon remains the same. Two technical reports, + IPD112 and IPD239, describe subsequent changes. - Printed copies of the Language and Graphics books are available from Jeffery - Systems (www.zianet.com/jeffery/books). All three books can be downloaded at - no charge from the Icon books page, www.cs.arizona.edu/icon/books.htm. + Printed copies of the Language and Graphics books are available from + Jeffery Systems (http://unicon.org/books/). All three books can be + downloaded at no charge from the Icon books page, + www.cs.arizona.edu/icon/books.htm. The Icon Programming Language Handbook, by Thomas W. Christopher, is available on the web at www.tools-of-computing.com/tc/CS/iconprog.pdf. @@ -171,101 +183,107 @@ Learning about Icon An on-line index to the Icon program library is found at www.cs.arizona.edu/icon/library/ipl.htm. - There is a large amount of additional information at the Icon web site, - www.cs.arizona.edu/icon. + There is a large amount of additional information at the Icon web + site, www.cs.arizona.edu/icon, including complete sets of back issues + of the Icon Newsletter and Icon Analyst. _________________________________________________________________ Implementations B1. What platforms support Icon? - Current implementations with graphics support are available for Unix - (including Linux) and Windows. The Unix implementation also runs on Darwin, - the Macintosh development environment, or the Cygwin environment under - Windows. Older versions of Icon are available for some other systems. An - alternative Java-based implementation for Unix, Jcon, is also available. + The current implementation of Icon is a Unix implementation. This + includes Linux, BSD, Solaris, Macintosh, and the Cygwin environment + under Windows. Version 9.5 of Icon has been tested on all these + platforms. - B2. How do I get started with Icon? + Older versions are available for Windows and some other systems. An + alternative Java-based implementation for Unix, Jcon, is also + available. - Version 9.4.3 of Icon for Unix can be downloaded from - www.cs.arizona.edu/icon/v943. Source and binary packages are available, each - with the complete Icon program library. + None of these environments includes a window-based development + environment. While Icon programs can open windows and use graphics, + programming is done using Unix editors and other tools from a command + shell. + + B2. How do I get started with Icon? - Version 9.3 of Icon for Windows is compatible at the source level with - version 9.4.3. It can be downloaded from www.cs.arizona.edu/icon/v93w.htm. - The Version 9.4.3 library can be obtained separately from - www.cs.arizona.edu/icon/v943. + The current version of Icon for Unix can be downloaded from + www.cs.arizona.edu/icon/current. Source and binary packages are + available, each with the complete Icon program library. - For older implementations, start at www.cs.arizona.edu/icon/implver.htm. - Jcon is at www.cs.arizona.edu/icon/jcon. + For older implementations, start at + www.cs.arizona.edu/icon/implver.htm. Jcon is at + www.cs.arizona.edu/icon/jcon. B3. Is there a Unicode version of Icon? - No. Icon is defined in terms of 8-bit characters, and changing this presents - several design challenges that would likely break existing programs. Also, - modifying the C implementation is probably infeasible, but a Unicode version - of Jcon might be possible. + No. Icon is defined in terms of 8-bit characters, and changing this + presents several design challenges that would likely break existing + programs. Also, modifying the C implementation is probably infeasible, + but a Unicode version of Jcon might be possible. B4. What happened to the compiler? - For a while, Unix distributions included both an interpreter and a compiler; - but the interpreter is is usually fast enough even for production work, and - most people found that using the compiler wasn't worth the extra compilation - time or the hassles involved. We no longer advertise the compiler or produce - binaries for it. It is still part of the source code distribution, and we - have not deliberately broken it, but we no longer support it and we cannot - offer help if problems arise. + For a while, Unix distributions included both an interpreter and a + compiler. The compiler was an interesting research project but it has + not been maintained and is no longer supported. The interpreter is + much easier to use and is generally quite fast enough, even for + production applications. _________________________________________________________________ Administration C1. What is the Icon Project? - The Icon Project is a name used by the group that distributes and supports - the Icon programming language. The project maintains the Icon web site at - www.cs.arizona.edu/icon. A non-commercial organization, the project is - supported by the Department of Computer Science at the University of - Arizona. + The Icon Project is a name used by the group that distributes and + supports the Icon programming language. The project maintains the Icon + web site at www.cs.arizona.edu/icon. A non-commercial organization, + the project is supported by the Department of Computer Science at the + University of Arizona. C2. How often is the on-line material updated? - New material is added when it's available. Established implementations - usually are updated only when there's a new version. This typically is every - year or two. The Icon program library is updated on a similar schedule. + The Icon implementation is now in maintenance mode, with new releases + produced only when necessary. This typically happens every few years + when a change in the Gnu tools cause the source to stop building. C3. 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 1960s. 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. Although it has similar - objectives and many similar capabilities, Icon bears little superficial - resemblance to SNOBOL4. - - Icon implementations were developed by faculty, staff, and students at the - University of Arizona, with significant contributions from volunteers around - the world. An Icon history by Ralph and Madge Griswold appears in the - preprints of the second History of Programming Languages Conference - (HOPL-II), ACM SIGPLAN Notices, March 1993 (Vol 28, No 3). + 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 1960s. 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. Although it has similar objectives and many similar + capabilities, Icon bears little superficial resemblance to SNOBOL4. + + Icon implementations were developed by faculty, staff, and students at + the University of Arizona, with significant contributions from + volunteers around the world. An Icon history by Ralph and Madge + Griswold appears in the preprints of the second History of Programming + Languages Conference (HOPL-II), ACM SIGPLAN Notices, March 1993 (Vol + 28, No 3). The name Icon is not an acronym, nor does it stand for anything in - particular, although the word iconoclastic was mentioned when the name was - chosen. The name predates the now common use of icon to refer to small - images used in graphical user interfaces. This sometimes misleads people - into thinking that Icon is designed to create or manipulate icons, but - there's no good solution to that problem. + particular, although the word iconoclastic was mentioned when the name + was chosen. The name predates the now common use of icon to refer to + small images used in graphical user interfaces. This sometimes + misleads people into thinking that Icon is designed to create or + manipulate icons, but there's no good solution to that problem. C4. Where is Icon going? - We continue to use Icon on a daily basis, but no significant changes are - planned. We expect to support the Unix version for the forseeable future, - and to distribute ports to other systems as supplied by volunteers. + We continue to use Icon on a daily basis, but no significant changes + are planned. We expect to support the Unix version for the foreseeable + future, and to distribute ports to other systems as supplied by + volunteers. - The Unicon project is developing an object-oriented language based on Icon. - For more information, see unicon.sourceforge.net. An earlier object-oriented - extension to Icon, Idol, can be found in the Icon program library. + The Unicon project is developing an object-oriented language based on + Icon. For more information, see unicon.sourceforge.net. An earlier + object-oriented extension to Icon, Idol, can be found in the Icon + program library. _________________________________________________________________ Support @@ -277,61 +295,59 @@ Support D2. 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: + 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: * For programming questions, submit a query to the Usenet newsgroup comp.lang.icon. * For porting assistance or Unix problems, contact icon-project@cs.arizona.edu. - * For problems with the Windows implementation, contact the implementor, - jeffery@cs.nmsu.edu. - * For general information and additional documentation, visit the Icon web - site: www.cs.arizona.edu/icon. + * For general information and additional documentation, visit the + Icon web site: www.cs.arizona.edu/icon. _________________________________________________________________ Programming E1. Why doesn't read() work with every? - every s := read() do {...} doesn't loop because read() produces a single - value and then fails if resumed. Other "consumer" procedures such as get() - and pop() work the same way. Use a while loop with these procedures, and - save every for use with generators such as !x or key(T). + every s := read() do {...} doesn't loop because read() produces a + single value and then fails if resumed. Other "consumer" procedures + such as get() and pop() work the same way. Use a while loop with these + procedures, and save every for use with generators such as !x or + key(T). E2. Why doesn't string invocation such as "foo"() work? - String invocation works if the procedure is present; the catch is that the - linker removes unreferenced procedures. To ensure a procedure's presence, - reference it in the main() procedure. A simple reference suffices, as in - refs := [foo, bar, baz]; it's not necessary to actually call it. + String invocation works if the procedure is present; the catch is that + the linker removes unreferenced procedures. To ensure a procedure's + presence, reference it in the main() procedure. A simple reference + suffices, as in refs := [foo, bar, baz]; it's not necessary to + actually call it. - (Why does the linker remove unreferenced procedures? Because this can save - huge amounts of memory for programs that use the library.) + (Why does the linker remove unreferenced procedures? To significantly + reduce the memory requirements of programs that use the library. There + was a time when this mattered.) E3. How can I call a C function? - You can't call an arbitrary C function, but if you're willing to write a - function to Icon's specifications, there are two approaches. Under Unix, - which provides loadfunc(), you can load one or more functions from a shared - library, and then treat them as if they had been written in Icon. Some - examples can be found in the cfuncs and packs/loadfuncs directories of the - Icon program library. The more cumbersome approach is to add code to the - Icon interpreter and rebuild it; some hooks are provided for this purpose. - Both approaches are discussed in Calling C Functions from Icon, - www.cs.arizona.edu/icon/docs/ipd240.htm. + You can't call an arbitrary C function, but you can load and call one + that is written to Icon's specifications. A tutorial appears in Icon + Analyst 36. Some examples can be found in the cfuncs and + packs/loadfuncs directories of the Icon program library. The Jcon implementation allows Icon programs to call Java code that is written to Jcon specifications. E4. Can I open a bidirectional pipe? - No, this is not possible. Although the concept is simple — write a line to a - program via a pipe, then read that program's output — it probably wouldn't - work. Most I/O libraries don't write anything to a pipe until they've filled - a buffer, and the most likely consequence would be a deadlock, with each - program waiting for the other to send more data. + No, this is not possible. Although the concept is simple -- write a + line to a program via a pipe, then read that program's output -- it + probably wouldn't work. Most I/O libraries don't write anything to a + pipe until they've filled a buffer, and the most likely consequence + would be a deadlock, with each program waiting for the other to send + more data. _________________________________________________________________ - This FAQ is edited by Gregg Townsend. It includes contributions from Ralph - Griswold, Cliff Hathaway, Clint Jeffery, Bob Alexander, and Todd Proebsting. + This FAQ is edited by Gregg Townsend. It includes contributions from + Ralph Griswold, Cliff Hathaway, Clint Jeffery, Bob Alexander, and Todd + Proebsting. |