An article at
http://users.pandora.be/koen.vandamme1/papers/tcl_fileformats/tcl_fileformats.html
(new version at:
http://www.gener8.be/site/articles/tcl_file_formats/tcl_file_formats.html
) discusses the ways one might write out Tcl data structures to disk to make it easier to reuse the data in a later execution, or to communicate it to another application.