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= Introduction to Icon and
== Under Construction Notes ==
This page is a work in progress. The objectives of this page are as follows:
* Provide a place to put detailed documentation or descriptions that can be referenced from task pages or category pages
* Provide something akin to a readers digest condensed version of the books and other references
* Some of the information may be more appropriately moved to Paradigm pages
The initial text of this page has been taken from [[Flow-control_structures#Icon_and_Unicon]]
== Purpose ==
The purpose of this page is to provide a Rosetta Code users with a enough supporting detail about Icon and Unicon to facilitate understanding and appreciation of these languages. More detail can be found in the online books.
== Icon and Unicon Differences ==
[[Icon|The Icon Programming Language]] was the successor of a series of non-numeric languages including Commit, SNOBOL, [[SNOBOL4]], and SL-5. Icon provided several innovations and improvements over its predecessors including: integrating the the powerful pattern matching capabilities of SNOBOL4 into a procedural language, banishing a number of unfortunate foibles, retaining the flexibility of a typeless langauge, reining in some programming side effects, keeping platform independence. Icon was one of the first bytecode languages undergoing continuous improvement from it's inception in the late 1970s.
Over the years various improvements, extensions, and experimental variants were added including a platform independent graphics interface, IDOL (an object oriented pre-processor), MT Icon (a Multi-Threaded variant), Jcon (an implementation in Java), and others. And while the graphics interface was integrated into Icon, many of these variants were not.
[[Unicon|The Unicon Programming Language]] integrated a number of these extensions into a single variant of Icon. Unicon includes object-oriented support, improved system interfaces, and messaging. Additionally, a number of syntactic improvements to the language and semantic extensions to some functions have been implemented. Because of this Unicon isn't completely a superset of Icon.
== Variables, Data Types, and Structures ==
=== un-Declarations ===
Icon and Unicon do not require strict static typing of variables as does languages like [[Pascal]], nor does it require type definitions to reserve space such as in languages such as [[C]]. In fact, variables may happily change type from one moment to the next. Knowing this you might expect that declarations are non-existent.
Declarations are optional and any undeclared variables are either (a) parameters to procedures or (b) local to procedures. This design decision ensured that Icon/Unicon are not susceptible to the kind of side-effects that the global nature of variables in SNOBOL4 led to.
Still, declarations are desirable for clarity and needed for a number of special cases:
* local - variables local to a procedure
* static - permanent variables that transcend individual calls of procedures. While not visible outside of a procedure they are visible between different instances and across recursion of a procedure.
* global - variables with global visibility
Additionally, the following declarations apply to non-variables:
* record - used to define a structure with named fields
* procedure - used to define a procedure and its parameters
* invocable - used to control program linking to ensure procedures are included and available if they are called (e.g. through string invocation)
* class - used to define an object class (Unicon)
=== Self-Descriptive Safe Types ===
=== Mutable and Immutable Types ===
== Operators and Procedures ==
=== Intuitive Generalizations ===
=== Strong Typing through Operators ===
=== Coercion: Implicit Type Conversions ===
== Program Flow ==
====Prelude about Goal-Directed Evaluation and Generators====
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