Version 32 of Icon

Updated 2013-04-02 01:09:08 by escargo

The word icon can have several meanings within the computing community.

For instance, an icon can be a graphical image used within a GUI application to represent some action to take. Tklib includes an ico package with specific icon-related capabilities.

The BWidget toolkit supports toolbars with icons very nicely.

You can get an excellent collection of beautiful icons, complete with the supporting software to integrate them into your Tk application, from Adrian Davis' Tk ICONS project.

See also:

Icon [L1 ] is a programming language with a long and rich history, although it is even more obscure than Tcl.

Also, see About Tcl and popularity

There are several points of similarity between the two languages, along with many more differences.

  • Interpreted with a byte-code compiler
  • Portable across a range of different systems
  • Built-in memory allocation and garbage collection
  • Portable graphical tool kit
  • High degree of introspection
  • Rich built-in data structures (character sets, lists, records, sets, strings, tables)
  • Invocation of procedures based on a dynamic string value
  • Two memory scopes, global and local
  • Strongly typed values, but untyped variables (SS: I don't agree this is a common point between Tcl and Icon).
  • Primitives for determining if a variable has a value
  • No "go to" statement

The data structures are implemented in a way that allows a substantial amount of polymophism. The syntax for iterating through all the values in a set, or all the elements in a list, or even all the characters in a string is pretty much the same.

Some of the differences are equally significant.

  • The syntax looks more like C than tcl
  • Many, many operators
  • Procedures can have local variables that are declared static instead of local so that they retain their values between invocations (for Tcl, see Static variables and variables in namespaces)
  • Parameters are passed by value (for primitive types) or reference (for structures)
  • No dynamic creation of procedures
  • No namespaces
  • Pattern matching is a normal extension of expression evaluation
  • Backtracking built into the language
  • Expressions can yield 0 or more values (not necessarily all at once)
  • Generators and co-expressions
  • Character set limited to 8-bit characters
  • Separate compilation of procedures (not a just-in-time compiler)

escargo 10/28-30/2002

ulis, 2005-04-22. (following text comprise excerpts from [L2 ])

Icon has notions of success and failure that added to the notion of generator permits thing such:

   sentence := "Store it in the neighboring harbor" 
   every i := find("or", sentence)
     do write(i)

which writes all the positions at which "or" occurs in sentence. For the example above, these are 3, 23, and 33.

Compare Tcl's

 % regexp -all -indices -inline or "Store it in the neighboring harbor"
 {2 3} {22 23} {32 33}

Other interesting notion is suspension:

   procedure findodd(s1, s2)
     every i := find(s1, s2) do
        if i % 2 = 1 then suspend i
   end

is a procedure that generates the odd-valued positions at which s1 occurs in s2. The suspend control structure returns a value from the procedure, but leaves it in suspension so that it can be resumed for another value. When the loop terminates, control flows off the end of the procedure without producing another value.

See continuation or coroutine.

MC: The book The Icon Programming Language went out-of-print, rights reverted to the authors who placed the book in the public domain, and PDFs online at [L3 ].

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