[NEM] ''Transparent'' values in Tcl, are those which directly represent
the value, as opposed to [handle] values which are more like pointers
or references in other languages. Transparent values include things like
lists, dicts (in 8.5) and strings. Transparent values are ''first-class'' in that
they can be passed directly to commands, and returned from commands.
Handles are first-class, but the things that they are handles for (what is
being pointed to) are not first-class, as they can only be passed around
via a handle. For instance, commands are a handle value - you pass
around the name of the command, rather than the command itself (Tcl
uses a hashtable or similar to map the name to the actual command
internally). On the particular issue of commands, see [TIP]s 187, 194,
and 196 which all try to introduce first-class transparent commands
into Tcl.
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