[GRASS-dev] Re: [GRASS-CVS] michael: grass6/gui/tcltk/gis.m mapcanvas.tcl, 1.52, 1.53

[Glynn Clements]

Hamish wrote:

> oh, and FWIW I figured out why my tcl exec solution was failing with:
>  ERROR: region <> not found
> It was trying to run `g.region ""`  (expands to `g.region region=""`)
> 
> It's redundant now, but for the record adding a "concat" fixed it:
> 
> -set regcmd [list exec "g.region" "-ug" $args]
> +set regcmd [list exec "g.region" [concat "-ug " $args]]
>  set retval [catch $regcmd result]

This is bogus. It will fail if $args isn't empty:

	% set args {foo bar baz}
	% set regcmd [list exec "g.region" [concat "-ug " $args]]
	% puts $regcmd
	exec g.region {-ug foo bar baz}
	% set args foo
	% set regcmd [list exec "g.region" [concat "-ug " $args]]
	% puts $regcmd
	exec g.region {-ug foo}

IOW, the entire list of arguments (including the "-ug") will be passed
to g.region as a single argument.

I'm guessing that you're focusing on the case where $args is empty:

	% set args ""
	% set regcmd [list exec "g.region" "-ug" $args]
	% puts $regcmd
	exec g.region -ug {}
	% set args ""
	% set regcmd [list exec "g.region" [concat "-ug " $args]]
	% puts $regcmd
	exec g.region -ug

If so, the correct fix is:

	set regcmd [concat exec g.region -ug $args]

E.g.:

	% set args ""
	% set regcmd [concat exec g.region -ug $args]
	% puts $regcmd
	exec g.region -ug
	% set args foo
	% set regcmd [concat exec g.region -ug $args]
	% puts $regcmd
	exec g.region -ug foo
	% set args {foo bar baz}
	% set regcmd [concat exec g.region -ug $args]
	% puts $regcmd
	exec g.region -ug foo bar baz

NOTE: if a procedure's last formal argument is named "args", it is
treated specially: $args will be a list containing all of the
remaining arguments. This allows variadic procedures to be
implemented.

If you are passing a list of arguments as a list (rather than as
individual arguments), use a name other than "args". Otherwise, the
list will get "wrapped" inside another list.

Only use "args" as an argument variable if the procedure is supposed
to be variadic.

-- 
Glynn Clements <glynn at gclements.plus.com>