While this topic might be regarded as merely a special case of the more general topic of "Extending Tcl", many newcomers to the subject conceive it in these more mechanical terms.

[...]

Variations:

• Critcl and so on
• compiled-in extensions
• "impedance-matching" loaders
• Incr TCL has Itcl_RegisterC function to register C functions as @function symbols in Itcl class members

Among the latter, Windows variants include

• Yet another dll caller
• ffidl
• dllcaller

and, in a different way,

• COM (in the broad sense, that is, including OLE and DCOM)
• DDE
• ActiveX
• SIMPL

[Mention SWIG.]

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For those broad-minded enough to replace "function" by process, TV recommends IPC:

TV Don't forget that a possibly completely platform independent method is to pass messages over a socket to a C-code based process. Example: [1]. Long ago I've made some automation scripts to generate the frame for this sort of method which is quite possible in tcl.

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