Chapter 18. Getting started with Tcl/Tk

18.1. Introduction to Tcl/Tk

Tool command language (Tcl) is a dynamic programming language. The interpreter for this language, together with the C library, is provided by the tcl package.

Using Tcl paired with Tk (Tcl/Tk) enables creating cross-platform GUI applications. Tk is provided by the tk package.

Note that Tk can refer to any of the the following:

  • A programming toolkit for multiple languages
  • A Tk C library bindings available for multiple languages, such as C, Ruby, Perl and Python
  • A wish interpreter that instantiates a Tk console
  • A Tk extension that adds a number of new commands to a particular Tcl interpreter

For more information about Tcl/Tk, see the Tcl/Tk manual or Tcl/Tk documentation web page.

18.2. Notable changes in Tcl/Tk 8.6

Red Hat Enterprise Linux 7 used Tcl/Tk 8.5. With Red Hat Enterprise Linux 8, Tcl/Tk version 8.6 is provided in the Base OS repository.

Major changes in Tcl/Tk 8.6 compared to Tcl/Tk 8.5 are:

  • Object-oriented programming support
  • Stackless evaluation implementation
  • Enhanced exceptions handling
  • Collection of third-party packages built and installed with Tcl
  • Multi-thread operations enabled
  • SQL database-powered scripts support
  • IPv6 networking support
  • Built-in Zlib compression

  • List processing

    Two new commands, lmap and dict map are available, which allow the expression of transformations over Tcl containers.

  • Stacked channels by script

    Two new commands, chan push and chan pop are available, which allow to add or remove transformations to or from I/O channels.

Major changes in Tk include:

  • Built-in PNG image support

  • Busy windows

    A new command, tk busy is available, which disables user interaction for a window or a widget and shows the busy cursor.

  • New font selection dialog interface
  • Angled text support
  • Moving things on a canvas support

For the detailed list of changes between Tcl 8.5 and Tcl 8.6, see Changes in Tcl/Tk 8.6.

18.3. Migrating to Tcl/Tk 8.6

Red Hat Enterprise Linux 7 used Tcl/Tk 8.5. With Red Hat Enterprise Linux 8, Tcl/Tk version 8.6 is provided in the Base OS repository.

This section describes migration path to Tcl/Tk 8.6 for:

  • Developers writing Tcl extensions or embedding Tcl interpreter into their applications
  • Users scripting tasks with Tcl/Tk

18.3.1. Migration path for developers of Tcl extensions

To make your code compatible with Tcl 8.6, use the following procedure.

Procedure

  1. Rewrite the code to use the interp structure. For example, if your code reads interp→errorLine, rewrite it to use the following function: 

    Tcl_GetErrorLine(interp)

    This is necessary because Tcl 8.6 limits direct access to members of the interp structure.

  2. To make your code compatible with both Tcl 8.5 and Tcl 8.6, use the following code snippet in a header file of your C or C++ application or extension that includes the Tcl library: 

    # include <tcl.h>
# if !defined(Tcl_GetErrorLine)
# define Tcl_GetErrorLine(interp) (interp→errorLine)
# endif

18.3.2. Migration path for users scripting their tasks with Tcl/Tk

In Tcl 8.6, most scripts work the same way as with the previous version of Tcl.

To migrate you code into Tcl 8.6, use this procedure.

Procedure

  • When writing a portable code, make sure to not use the commands that are no longer supported in Tk 8.6: 

    tkIconList_Arrange
tkIconList_AutoScan
tkIconList_Btn1
tkIconList_Config
tkIconList_Create
tkIconList_CtrlBtn1
tkIconList_Curselection
tkIconList_DeleteAll
tkIconList_Double1
tkIconList_DrawSelection
tkIconList_FocusIn
tkIconList_FocusOut
tkIconList_Get
tkIconList_Goto
tkIconList_Index
tkIconList_Invoke
tkIconList_KeyPress
tkIconList_Leave1
tkIconList_LeftRight
tkIconList_Motion1
tkIconList_Reset
tkIconList_ReturnKey
tkIconList_See
tkIconList_Select
tkIconList_Selection
tkIconList_ShiftBtn1
tkIconList_UpDown

    Note that you can check the list of unsupported commands also in the /usr/share/tk8.6/unsupported.tcl file.