[CMcC] {et al} 2008-07-08:

Tcl contains some semantic equivalences.  ''~~'' can be read as
''approximates''.  Add more if you find them.  The idea is to find cases where
''there is more than one way to do it''.  The hunt is on.

In the following examples, `[lindex]` is used as the identity command, i.e.,
a command that returns its argument, verbatim.


** `$varname ~~ [set] varname` **

Example:  Given

======
set abc 123
======

The following command are equivalent

======
set xyz $abc
set xyz [set abc]
======



** `script ~~ [eval] {script}` **

See [Many ways to eval]



** `lindex "string" ~~ [subst] {string}` **

Example:

Using `string` can result in quoting hell for some strings while using subst is
more verbose but "cleaner".

[[replace with example]]



** `"$list1 $list2" ... ~~ [concat] $list1 $list2 ...` **

Example:

======
#given
set colors {taupe puce heliotrope}
set countries {Djibouti Brazil Azerbaijan}

#equivalents
set var "$colors $countries"
set var [concat $colors $countries]
set var [list {*}$colors {*}$countries]
set var [string cat $colors { } $countries]
======


** `lindex {a b c ...} ~~ list a b c ...` **

Example:

======
set var "1 2 3"
set var {1 2 3}
set var 1\ 2\ 3
set var [list 1 2 3]
======



** global varname ~~ ::varname **

'''`[upvar] #0 varname varname ~~ ::varname`'''

Example:

======
set abc $::env(HOME)
======

or

======
global env
upvar #0 env env2
set abc $env(HOME)
set abc2 $env2(HOME)
======


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