Documentation is at http://tcllib.sourceforge.net/doc/struct_set.html 

This part of the [struct] (data structures) submodule of [tcllib] provides procedures for manipulating sets.
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''[escargo] 16 Feb 2007'' - The documentation assumes that you can guess how sets are implemented.

For example, there are no examples.  The published interface does not say how to create a set,
nor how to determine the value of a set.

Apparently set are built on top of lists; wherever a set argument is used by a ::struct::set
subcommand, a list will work.

Therefore, there is no need to have a set constructor (since you can just use a list).
There is also no need for a separate iterator over a set, since a set is a list.

But the documentation does not make that clear.
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[[
[Category Package], see [struct] / [tcllib] |
[Category Mathematics] |
[Category Data Structure] |
]]