Updated 2014-12-23 00:40:36 by pooryorick

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  edit

Example: Given
set abc 123

The following command are equivalent
set xyz $abc
set xyz [set abc]

script ~~ eval {script}  edit

See Many ways to eval

lindex "string" ~~ subst {string}  edit


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 ...  edit

set colors {taupe puce heliotrope}
set countries {Djibouti Brazil Azerbaijan}

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 ...  edit

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

global varname ~~ ::varname  edit

upvar #0 varname varname ~~ ::varname

set abc $::env(HOME)

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