Purpose: describe the various methods available within Tcl for code reuse.


   Cut/copy and paste:   user maintains a series of text files containing tcl code and then just copies the text when needed.

   source:   tcl has a command called '''source''' which reads a file, treating the contents just as if they were a part of the original file.

   load:   tcl has a command called '''load''' which is used to attach a dynamically loadable object extension to the current library.

   packages:   See Will Duquette's "Guide to Success with Namespaces and Packages" at http://www.wjduquette.com/tcl/namespaces.html .

   unknown:   tcl has a command called '''unknown''' which is invoked whenever the tcl interpreter is unable to determine a particular command.  unknown does some processing and can provide dynamic sourcing of functions.  Details go here. See [Radical Language Modification] for examples how to deal with the unknown.

   exec:   '''exec''' is a tcl command used to invoke a stand alone command.  This command can be written in any language supported by the system.  [Cameron Laird] wrote a nice explanation of some of the common questions about exec on comp.lang.tcl a while ago - see http://x8.dejanews.com/getdoc.xp?AN=389920667 for the article.  This is one of the most common ways people set up Tcl commands to run non-Tcl commands.

   pipe:   tcl supports, in the '''open''' command, the ability to invoke a stand alone command, opening an input and/or output pipeline to it.  It is started in a manner similar to the exec command.  This is one means used to write a tk interface to 'wrap' around an existing program.

   proc:   tcl of course supports the ability to write functions, which is a mechanism many languages provide for writing code once and then calling it multiple times.

   expect:   the [Expect] extension/program is a Tcl package designed to write 'wrappers' around existing tcl or non-tcl programs.  It is a method common to the exec above, but with extensions designed to make interacting with character based applications easier.


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Be sure to read [Concepts of Architectural Design for Tcl Applications] for a great article on this topic.

I hope people stopping by this page will update the above descriptions to fill in a lot of the details (where does pkgIndex, tclIndex come in - what other options are available, etc.).



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