Troubles when trying to use Tk conditionally

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Hi everyone, here's a simple but annoying problem: I'm trying to use Tk in a multiplatform script. The windows version is packed into a self-contained .exe with PAR::Packer, so on Windows, I can pack in Tk and it works out of the box for the user. On other platforms, I want the script to be able to run without installing Tk.

Now, based on a previous thread, I'm using use if $^O eq "MSWin32", "Tk"; to load Tk conditionally. So far, so good, but of course the code later on contains the compulsory MainLoop; line. This causes a problem on *nix, as I get an error about the Bareword "MainLoop". Understandable, as "MainLoop;" makes no sense to the perl compiler in the absence of the module. if ($gui eq "on") {MainLoop} doesn't help of course, because the error is thrown at compile time. I could just switch off strict subs and warnings and the script would run fine, but that's not very elegant, is it?
So, is there an easy way to run the script with strict and warnings on?

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Re: Troubles when trying to use Tk conditionally by moritz (Cardinal) on Feb 04, 2011 at 14:55 UTC
Use `MainLoop()`. The parenthesis force the perl compiler see the identifier as a subroutine name, not a bareword. Perl 6 - second systems done right	[reply] [d/l]
Re^2: Troubles when trying to use Tk conditionally by elef (Friar) on Feb 04, 2011 at 15:12 UTC
Thank you, that works. I wrote it as bart says: it doesn't get called when no Tk module is available, so there's no error thrown there, either.	[reply]
Re: Troubles when trying to use Tk conditionally by bart (Canon) on Feb 04, 2011 at 15:05 UTC
Try `BEGIN { *MainLoop = \&MainLoop; }` [download] near the top of your script (near the use statement), or plain `Mainloop();` [download] instead of the current call. Even though the function doesn't exist, if it isn't called, it won't complain.	[reply] [d/l] [select]
Re^2: Troubles when trying to use Tk conditionally by moritz (Cardinal) on Feb 04, 2011 at 15:19 UTC
`BEGIN { *MainLoop = \&MainLoop; }` [download] Or a bit less ugly (IMHO): `use vars qw/&MainLoop/;` [download] Perl 6 - second systems done right	[reply] [d/l] [select]
Re^3: Troubles when trying to use Tk conditionally by bart (Canon) on Feb 04, 2011 at 18:25 UTC
I had thought about that, but I was unsure that it works. There's also `use subs`.	[reply]
Re: Troubles when trying to use Tk conditionally by cdarke (Prior) on Feb 04, 2011 at 16:30 UTC
I rather like this solution: `use if $^O ne "MSWin32", "constant" => "MainLoop";` [download]	[reply] [d/l]
Re: Troubles when trying to use Tk conditionally by elef (Friar) on Feb 04, 2011 at 17:41 UTC
What if I wanted to allow non-Windows users to use the Tk gui if they are willing to install Tk themselves? Could I just do `if ($gui eq "on") {require Tk}` and simply sidestep compile-time checking of the module's availability? I could set the $gui variable based on the platform and the user's settings.	[reply] [d/l]
Re^2: Troubles when trying to use Tk conditionally by elef (Friar) on Feb 05, 2011 at 15:29 UTC
I did some testing, `if ($gui eq "on") {require Tk;import Tk}` works fine so far.	[reply] [d/l]