TCLA
Tcl Community Association
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TCLA

Birds of a feather flock together

Tcl/Tk Conference: 2007

The 2007 Tcl Conference was held in New Oleans, LA in the heart of the French Quarter. As ever, New Orleans was a treat to visit.

Our invited guest was Miguel Sofer. Miguel has been active in reworking the Tcl interpreter internals and explained the rationale and results of The Great (internal) Var Reform of 2007

Our Keynote speaker was Damon Courtney with a talk on developing seamless cross platform applications with Tcl/Tk.

A copy of the proceedings can be purchased as hardcopy at the Tcl Community Association Press storefront on Lulu.

GUIs and GUI Techniques


Remzi Arpaci-Dusseau
Making Beautiful Graphs with ZPlot
This paper introduces Zplot, a Tcl library for making two- dimensional data plots. Zplot provides a simple set of primitives that allow users to input and manipulate data, plot said data in a variety of formats, and decorate the re- sulting graphs with axes, labels, and other textual accents. Zplot then outputs encapsulated PostScript for ease of in- clusion in technical documents.

Ron Fox
Tcl/Tk Tools for EPICS Control Systems
The Experimental Physics and Industrial Control System (EPICS) is a control system in wide use in the control systems of accelerator laboratories across the world as well as in large-scale particle physics experiments. This paper will describe a Tcl package that provides access to EPICS control systems and a set of widgets that allow user interfaces to EPICS systems to be easily constructed. The extension will be compared and contrasted with the et_wish EPICS aware extended wish, and a justification for choosing to write a new extension will be given.

Tcl/Tk Development and Debugging Tools


Florian Murr
XTrace: A High Level Extension of Tcl Trace
In this paper two Tcl-packages written in pure XOTcl are presented. The first "Xcom" is yet another socket-communication package; the second "Xtrace" uses Xcom to provide an observer command across multiple processes called "xtrace" that is modeled along the lines of the well-known Tcl "trace" command, but much more high-level.

Axel Nagelschmidt
Eti: An Extensible Framwork For Creating Applications
Writing a complete editor is possible after one month of learning TCL!

Usage of object orientation seemed to be a good idea: Have a mini editor for any kind of text. Derive HTML editor, TCL editor etc. from this. Have a set of classes needed for graphic programs, derive different graphical drawings / simulations from this. Specify a set of common used actions to include into the menu or a toolbar Have multiple instances of the same type, so can use a notebook with several tabs incr TCl offering classes and incr TK offering megawidgets like notebook seemed natural

But (1) ... incr TK seemed to be more complicated than necessary incr TK seemed to be slow because of code overhead. This led to the development of the Eti Framework.


Invited Talk


Miguel Sofer
The Great (internal) Var Reform of 2010
The Var struct used as internal representation for Tcl's variables currently contains six pointers and 2 integers, or 32 bytes on a 32-bit platform. For variables in hashtables, be they namespace variables or array elements, a hash entry structure consuming a further minimum of 24 bytes (but typically 28) is also maintained. These requirements reflect a history of the structure, and are far from optimal. We will explain the requirements that have to be satisfiedd, how they gave rise to this structure, and a way to thin them down considerably: compiled variables are reduced to 8 bytes (75% reduction), hashtable variables to a grand total of 24 bytes (60% reduction) . Further performance advantages of the new implementation will also be described.

Tcl as Glue (Traditional Tcl)


Michael Cleverly
Tcl In the Middle
Tcl has long been recognized as an excellent language to glue existing components together to create new applications. Tcl is just as useful when interjected into the middle of functioning N-tier "enterprise" systems. SockSpy is probably the best known example of a "man in the middle" Tcl application. What may not be as widely appreciated, however, is that Tcl's strong TCP sockets and event- drive I/O make construction of custom "man in the middle solutions" (or proxies) quite straight- forward. These custom solutions solve real business problems often at a fraction of the cost of other potential solutions. This paper will look at a handful of examples where Tcl has been employed in this manner at Intermountain Healthcare.

Kevin B. Kenny
An ODE Solver for Tcl: Old Fortran in a New Interface
LSODAR is a Fortran subroutine for integration of ordinary differential equations that has been actively maintained for over twenty years and gives high-quality results for a variety of problems. This paper demonstrates how such a "dusty deck" can be adapted to interface cleanly to a modern high-level language like Tcl, be made safe to use in the presence of threads and recursion, and take advantage of the symbolic computation capabilities available to Tcl. The result is an ODE solver for Tcl that is production-ready, at the expenditure of considerably less effort than it would take to develop comparable capabilities targeted specifically at Tcl. It presents a few tricks that should be handy in connecting other legacy Fortran applications to Tcl.

Tcl Applications


Will Duquette
Anatomy of a Large Application: Architectural Patterns and Solutions
JNEM, the Joint Non-kinetic Effects Model, is a large simulation application. Written almost entirely in Tcl/Tk, it makes architectural use of the Snit object system and the SQLite3 database engine. This paper addresses a number of architectural patterns and solutions that have been found useful during the two- plus years of JNEM development. Patterns include the three-layer package architecture (application, domain, and utility); Snit types as application modules; saving and restoring application state; the database-backed objects; SQLite3 as an application memory debugger; and a generalization of the scrollbar/scrollable pattern.

Clif Flynt
Twelve Years of TclTutor
TclTutor is a Computer Aided Instruction application for learning the Tcl programming language.

This paper discusses the application's development and some of the technical details, along with lesson's learned and potential future work.


Tcl Does Data(bases)


Sean Woods
General Purpose Database Interface Adaptor for Tcl
TDIF is a uniform methodology for accessing external data within Tcl.

Its genesis stems from a need on my part to have the same software run under multiple platforms with different drivers to access MySQL. One distro of linux would ship with tclmysql. Another would ship with mysqltcl. Windows ships with tclodbc. And then there was the change in mysqltcl's interface between mysql_ and mysql::.

At the same time sqlite was coming into it's own, and I found myself replacing some MySql applications with it. I was also having to occasionally dump data out of MS Sql and MS Access. Being a lazy programmer, I developed a shorthand for all of the various database interactions I needed, and then wrote a suite of tools to convert that shorthand to the native interface of the storage engine.

TDIF is my attempt to adapt my own techniques, developed over time, into a formal interface.


Karl Lehenbauer
Speed Tables
Speed tables provides an interface for defining tables containing zero or more rows, with each row containing one or more fields. The speed table compiler reads the table definition and generates C code to create and manage corresponding structures, currently producing a set of C access routines and a C language extension for Tcl to create, access and manipulate those tables. It then compiles the extension, links it as a shared library, and makes it loadable on demand via Tcl's "package require" mechanism.

Speed tables are well-suited for applications for which this table/row/field abstraction is useful, with row counts from the dozens to the tens of millions, for which the performance requirements for access or update frequency exceed those of the available SQL database, a C compiler chain is available, and the application does not require "no transaction loss" behavior in the event of a crash.


Gerry Snyder
GEB: SQLite in Tcl/Tk
GEB is a Tcl/Tk program for displaying and manipulating SQLite databases. Each of its major functions is stored in an SQLite table. It has much of the functionality of the SQLite stand-alone executable, plus spreadsheet-like table display, nearly complete ALTER TABLE functions, SQLite version 2 to version 3 conversion, the ability to execute a table as either SQL or Tcl, and a few other functions I had a need for. The name GEB was chosen because using an SQLite database to store the program which displays and modifies the SQLite database itself seemed reminiscent of the "self reference at a higher level" which was a recurring theme in the book "Godel Escher Bach: An Eternal Golden Braid." If you insist on interpreting it as an acronym, it could stand for "Gerry's Experimental Box," but that is really a backronym.

Tcl Does Web


Gerald Lester
Using and Providing Web Services in Tcl
This paper discuss how to call Web Services from Tcl using the WebServices for Tcl package and how to provide, under Tcl based Web Servers, WebServices written in Tcl. Also discussed is how Web Service data is represented in Tcl.

Programming Techniques


Donal K. Fellows
OO For Tcl
For the past two years, I have been working on developing a new OO system for Tcl that is intended to serve as a basis for a wide range of OO styles. In this pa- per, I will describe and explain the current status of the work, discuss the issues involved in producing a high-performance flexible OO system, and describe a number of issues that have been encountered during work (with Arnulf Wiede- mann) to build a version of [incr Tcl] on top of the core OO system.

Kevin B. Kenny
Symbolic Differentiation in Tcl: Re-using the Tcl Parser for Symbolic Algebra
Symbolic differentiation is one of the easier problems in symbolic algebra; it is often presented as a student exercise in artificial-intelligence courses. Even though it is easy, it remains useful (and often underutilized) for mathematical computations such as root- finding, minimization and maximization of functions, and solving ordinary differential equations.

The most time-consuming part of writing a symbolic differentiator, in many languages, is writing a parser for the expressions to be differentiated. Fortunately, Tcl, being an interpretive language, comes with a parser for expressions that is available at run time. While the parser is not normally exported to scripts, the parser interface that the instrumentor in TclPro uses allows for script access via an extension. One advantage to using the built-in parser is that the programmer can be certain that the language of expressions to be differentiated is exactly the language of expressions to be evaluated.


Philip J. Mercucio
Poet: An OOP Extension to Tcl Supporting Constraints, Persistence, and End-User Modification
Poet (Prototype Object Extension for Tcl) extends the Tcl language with objects featuring dynamic, prototype-based inheritance, persistence, and one-way constraints between object attributes. Poet includes wrappers around the Tk and BWidget widgets that are automatically generated using introspection. This paper also describes Poetics (Poet Integrated Construction Set), a sub-project within Poet to create tools to allow a Poet application's code and user interface to be modified by the end-user, from within a running Poet application. The goal of Poetics is to provide some of the functionality of an integrated development environment to the user of a Poet application. An object inspector and code editor are the beginnings of the Poetics toolset.