'''Background'''

TIP #144 ''Argument Expansion Syntax''
[http://www.tcl.tk/cgi-bin/tct/tip/144.html]
(and the earlier TIP #103 ''Argument Expansion Command''
[http://www.tcl.tk/cgi-bin/tct/tip/103.html])
proposes to add syntax to Tcl to perform argument expansion in a safe
and efficient manner.

For example, instead of having to write:

 eval [linsert $args 0 exec $program]

The TIP would allow one to say:

 exec $program {}$args

where the leading '''{}''' indicates that the remainder of the
word shall be parsed as a list (after applying the usual substitution rules),
and each element of the list is passed as a separate argument to the command.

Naturally, there has been a great deal of discussion about what
syntax should be used to indicate argument expansion.  The two
most popular options seem to be {} and ` (backquote).

The main advantage of the {} syntax is that it can be added to
Tcl 8.5 without breaking backwards-compatibility,
as such usage is currently a syntax error.
Any other option would have to wait until Tcl 9.0.

A similar poll was conducted on the tcl-core mailing list. The result
is on the [Argument Expansion Poll Summary] page.

'''Poll'''

The purpose of this poll is to get a feel for the Tcl community's
preferences regarding the proposed syntaxes.
The poll is in two parts: the first asks which syntax would be preferable
''if backwards compatibility were not an issue''.
The second asks if the backwards-compatible syntax would be
acceptable if it meant the feature could be introduced earlier.

Please vote by signing your name or initials after the proposed option.

Discussion moved to [DISCUSSION: Argument Expansion Syntax]

'''Part 1: which syntax do you prefer?'''

''Option 1: leading {}'':
[Vince], [RS], [Roy Terry], [Jeffrey Hobbs], [EB], [Andreas Leitgeb], [JMN]

''Option 2: leading `'':
[Joe English], [ramsan], [SO], [US], [MC], [NEM], Heiner Marxen

''Option 3: other (please specify)'':
   * ''leading {expand}'' [DGP], [Daniel Steffen], [MS], [KBK], [Peter Spjuth], [de], [Donald Arseneau], [JBR]
   * ''$$foo'', ''$[[foo]]: [Lars H]
   * ''[[expand <whatever you want expanded>]]'' If someone can do it: [Steve Redler IV], [MAK], [Peter De Rijk], [TR], [Jacob Levy], [TP], [davidw], [Salvatore Sanfilippo], [PT], [Joe Mistachkin], [TFW]
   * ''^^$foo and ^^[[foo]]'' : [Setok]
   * Added functionality to Tcl that allows "macro" commands: commands can edit the calling command line. Dangerous in a semi-Tclish fashion. F.ex.  file join [[expand $MyList]] : [Setok] Scott Gargash, [Joe Mistachkin] (see [lconvert]), [MAK] (Well, I'm confused by the different "expand" options.  See [http://sourceforge.net/tracker/index.php?func=detail&aid=781929&group_id=10894&atid=310894]: same idea, but simpler than lconvert.)
   * paired backquotes meaning eval and expand (see [Discussion: Argument Expansion Syntax]): Scott Gargash
   * add switch to eval to control expansion of args. [Larry Smith], [Joe Mistachkin]
  eval arg1 arg2 arg3 arg4 arg5    ; same as before - expands all args
  eval -only { arg4 }              ; expands arg 4
  eval -only { arg1 to arg3 }      ; expand arg 1 to arg3
  eval -- -only arg2               ; -- turns off switch processing, -only just another arg to expand
   * '''Just use a postfix *'''  As in cmd $*var or  [[*cmd]] , has small impact on backwards compatibility. This syntax places expansion back at the parser backend where it has already detected special chars of either $ or [[. [PWQ] [MSW] (although I prefer ruby's *[[cmd]] or *$var)

''Option 4: neither'':
marc, THIRION, [lv] (as long as it truly can be provided as a command) [George Peter Staplin], [Jacob Levy]: (It has proven to be simple enough to implement ''expand'' in pure Tcl.  Therefore I feel that neither is worthy of the trouble.), Bradipo 

''Option 5: anything, just give me the functionality'':
[KPV], [Andreas Leitgeb], [schlenk]

''Option 5a: anything that gives the functionality but which isn't too ugly and which won't be too typo-inclined'':
[DKF], [rmax], [ulis]

'''Part 2: Is {} acceptable for Tcl 8.5?'''

''Yes, {} is acceptable'': [DGP], [Vince], [Daniel Steffen], [RS], [KBK], [Peter Spjuth], [Roy Terry], [EB], [Andreas Leitgeb], [DKF] (if we must), [NEM], Heiner Marxen, [JMN], [Lars H]

''Yes, ` is acceptable (never mind the slight chance of breakage)'': [US], [DKF] (if we can stand that much subtle incompatability)

''Yes, [[expand]] is acceptable, and it is also back-portable to older Tcl versions (noone yet came up with a convincing argument that required additional syntax and was not doable with a command)'': [Jacob Levy], [Steve Redler IV], [TP], [PT], [Joe Mistachkin], [JBR], [TFW]

''Yes, -only is acceptable'': [Larry Smith]

''Yes, anything is acceptable'': [KPV], [ulis] [MSW]

''No, wait until Tcl 9 to add the feature'':
[Joe English], marc, THIRION, [SO], [Setok], [schlenk], Scott Gargash, [MC], [rmax], [davidw], [Salvatore Sanfilippo]

''Not if this functionality can be achieved in some other manner'': [lv], [Jacob Levy], [Joe Mistachkin] (seems it can be implemented as a command)

''No, we do not need this functionality'': ---

''Just skip Tcl version 8.5 and release v9 as next version'': [ramsan]  I'm cool w/this, too. [Larry Smith] [Setok]

''Skipping Tcl 8.5 would be a horrible thing to do'': [Joe Mistachkin]

''If a new syntax rule is added in 8.5, it should be permanent.  No new different rule for 9.0'' [Clif Flynt]