Richard Suchenwirth 2001-06-10 -- Never change a running system, some of them say. But a Tcl interpreter with its accessories is a changing system from startup (every newly defined proc changes the language, for instance), and it's easy to extend or modify it while it runs.

Stefan Haefele wrote in comp.lang.tcl: I am trying to programm a user interface, which allows to add dynamically modules to this interface. The modules are tcl source files with several functions. Now I have problems to call the functions from the added tcl file.

Is there any easy way to let my application know where to call those functions?

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Easiest way (pedestrian):

Assume you have your modules in Tcl files like 'module1.tcl' which contain only procedure definitions (well, maybe some variable settings too): For each module you want, just call source:

        source my/module/dir/module1.tcl

Here procs with the same names can be defined in different modules. The last one you source wins.

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Classic way (auto):

Have your modules in one place (or few), create a TclIndex there (a Tcl script telling which file to source in order to get what proc). For this method, you'd better not have equal-named procs in different files, otherwise it's hard to predict what is sourced last. At startup of your application, just say

        lappend auto_path my/module/path ...

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Modern way:

Look at the package command. In your module file, write

        package provide mymodule1 1.5

Make sure you have a valid package index. This Tcl source file describes what actions to take if a package is required. In your application, demand

        package require mymodule1 1.5

and all procedures that your package provides are available.

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Finally, Tcl modules are packages designed to load very quickly - a module is a single file in one well-defined place (no search necessary).

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For experimenting, an interactive console is always great. As a starting point, look at a minimal console.

Don Porter has provided a console for Unix.

This console is known to work on Linux, win9x, and MAC.

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George Peter Staplin 2006.08.01 - Whim has an interactive console, and my primary Tcl code editor ProcMeUp has an "Attach" option that works with the "Sync" button to send updated procs to a running attached application (via send). It's much faster than restarting an app. I wish I had done this long ago.

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Something that might be desired is the ability for the user to specify new directories or packages to be added dynamically, rather than hard coded packages. This should be simple - I believe if you take a look at tkconsole, it is already set up to discover what packages are known to tcl and dynamically setting of a menu (only at startup time I think though - too bad it doesn't notice when new things are installed...)

schlenk The basic package require mechanism detects new packages in the auto_path. You just have to require a nonexisting packages or use some of the more elaborate, but better, constructs always recommended by dgp. This indexes all packages and you can see what's there with package names.

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RS 2007-10-04: One new and very fascinating way is to change the system by adding C functions interactively, e.g. with Odyce:

 31% critcl::cproc sigmsg {int i} char* {return Tcl_SignalMsg(i);}
 32% sigmsg 2
 interrupt

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