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 [extension]s
   * "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]




[[Mention [SWIG].]]
----
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: [http://mini.net/tcl/10449]. Long ago I've made some automation scripts to generate the frame for this sort of method which is quite possible in tcl.