Note that 

 eval exec $program $args
is not an adequate substitute for 
   eval [linsert $args 0 exec $program]
or
  exec $program {}$args
since it breaks when $program contains spaces.


''Option 4: leading @'':
[Larry Smith]  If you favor a leading character then "@" is easy to
see and read, much more so than `.

   * So... this means [Larry Smith] has no need for the [text] widget?


''Option 4: $(<whatever you want expanded>)'':
[Larry Smith] Personally, I prefer marking a particular string or set
of strings for an additional parsing/substitution pass using something that is
reminicent of the current syntax.  $([[cmd]]) or $([[cmd1]] [[cmd2]]) marks things
clearly as being expanded.  After all, it is the $ that signifies substitution,
not the {}.

   * $([[cmd]]) is already legal syntax within variable substituition and shouldn't be mixed up with expansion.

----

[Jacob Levy] July 28, 2003: What the example above tries to achieve seems to be possible without any new syntax, using a procedure called
apply, which behaves as follows:

 set l {a b c d e}
 apply list $l $l
 ==> {a b c d e a b c d e}

The definition of apply is that its first argument is a function that is applied to rest of the arguments which are evaluated and their values
are collected into a list.

The definition of apply is probably something like:

 proc apply {fn args} {
     set l ""
     foreach a $args {
         set l [lconcat $l $a]
     }
     return [eval $fn $l]
 }

 proc lconcat {pre el} {
     set l $pre
     foreach e $el {lappend l $e}
     return $l
 }

Now there may be more to TIP #144 that is not covered by this; however, at least for the given example, no new syntax is needed for implementing the functionality in Tcl.

[DGP] For this specific example, [[apply]] would be enough, yes.

When you extend things to get a command that can solve '''all''' of
the problems addressed by the proposed syntax, you end up with the
[[expand]] command proposed in TIP 103.

TIP 103 was considered and rejected.

Can we move on now please?

[DGP] For that matter, [[apply]] will not even work for the [[exec]] example
above (when ''$program'' contains spaces).

[Jacob Levy] Fixed the $args handling, above. To handle $prog with spaces in it, you'd need to pass [[list $prog]] to the invocation of apply.

[TP] I like the '''apply''' option best.  I would suggest that the apply command could have it's own ''mini-language''
(ala format, regexp, etc) using the {} or ` formatting.  E.g.

   apply {somecommand {}$expand_this $but_not_this}

[DGP] The "special command with its own mini-language" approach
was TIP 103.

----
[KBK] (2003-07-28) I ''know'' that I have code that will break with
the backquote syntax.