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From: [email protected] (Peter Prymmer)
Newsgroups: comp.lang.perl.tk,comp.lang.perl.announce,comp.answers,news.answers
Subject: comp.lang.perl.tk FAQ part3 of 5
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Date: Mon, 07 Oct 1996 17:21:23 GMT
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Perl/Tk FAQ part 3 of 5 - More Programming
******************************************


______________________________________________________________________



10. How do I get a Canvas to ... ?

The Canvas widget is the most configurable and versatile. With versatility
comes complication however, and it is certainly deserving of its own
special section within this FAQ...

You might also see the examples in the widget demo especially the
"canvas item types" selection (which runs the items.pl demo script).

______________________________________________________________________



10.1. Display a bitmap?

Unlike other widgets the Canvas does not take the -bitmap
configuration option. One of the ways to place things - including bitmaps
- onto a Canvas is to call create on it. To emphasize how a Canvas
handles bitmaps differently from the configurable widgets let me assume
that you wanted to specify the 'hourglass' built in bitmap in the following.
(For more on xbm file specification see a previous question [9.9] within
this FAQ.) Here is a way to combine the Canvas; and create; calls:

    my($canvar) = $main->Canvas();
    my($bittag) = $canvar->create('bitmap',10,10, -bitmap=>'hourglass');
    $canvar->pack;

You can also create an image that will display a bitmap (plus a whole lot
more):

    my($canvar) = $main->Canvas();
    my($bitmap) = $main->Bitmap(-data => $data);
    my($bittag) = $canvar->create(qw(image 10 10), -image => $bitmap);
    $canvar->pack;
    MainLoop;

______________________________________________________________________



10.2. Erase a display?

To erase something like a bitmap call delete on the item. Assuming your
Canvas tag is $canvar and your item tag it $bittag (as in the previous
[10.1] question) then the call proceeds like:

    $canvar -> delete($bittag);

This is of course useful in a callback. For example to configure a Button
to do your deletion for you you could say something like:

    $main->Button(-text   => 'clear',
                  -command=>sub{$canvar -> delete($bittag)}
                 )->pack;

To remove an entire MainWindow() call the withdraw() method:

    $main -> withdraw;

______________________________________________________________________



10.3. Display an Image?

Just as for the other widget types there is a two step process of first getting
a "Photo" handle on the file of interest. For the Canvas (unlike the other
widgets) one then makes a call to create an image as in the following
example where 'IMG' is the Photo handle for a GIF file that comes
distributed with the Tk kit (it just happens to be handled in this example
via the scalar variable $img):

    #!/usr/bin/perl -w
    use strict;
    use Tk;
    my $main = new MainWindow;
    my $canvar = $main ->Canvas;
    $canvar->pack;
    my $file = 'demos/images/earth.gif';
    my $img =
     $canvar->Photo( 'IMG',
                     -file => Tk->findINC($file) );

    $canvar->create( 'image',0,0,
                     '-anchor' => 'nw',
                     '-image'  => $img );

    MainLoop;
    __END__

______________________________________________________________________



10.4. What things can be created on a Canvas?

The following types can be used in $canvar->create calls:

    arc        sections of circle
    bitmap     for X11 bitmap files/builtins
    image      for Photo image types (gif, xpm, xbm, ...)
    line
    oval       includes circles
    polygon    may be -filled
    rectangle  may also be -filled
    text       similar to Text widget primitive
    window     allows embeddding of other widgets

______________________________________________________________________



10.5. How do I redraw a line on a Canvas?

By calling the ->coord method on the item as in the following example:

    #!/usr/bin/perl
    use Tk;
    $m = MainWindow->new;
    $c = $m -> Canvas;
    $i = $c -> create('line', 0,0 => 50,50 );
    $c -> pack;
    $b = $m -> Button('-text' => 'extend',
                      '-command' => sub{push_it($c,$i)},
                     )->pack;
    MainLoop;

    sub push_it {
        my ($canvas, $line) = @_;
        $canvas -> coords($line, 0,0 => 100,100 );
    }

Thanks to Christopher Dunn and Harry Bochner
<[email protected]> for providing this question and answer.

______________________________________________________________________



10.6. How do I use the Canvas as a geometry manager?

In a call to create a window (or anything) on your Canvas you need to
specify its position - this is in part how a Canvas can be used as a
geometry manager. e.g.:

    my($bittag) = $canvar->create('bitmap',10,10, -bitmap=>'hourglass');

Specifies the x=10, y=10 screen pixel location (from the upper left). Other
possible units are:


    tag  unit             example
         pixels           25,50   # i.e. no unit tag at all
    m    milliimeters     10c,20c
    c    centimeters      1c,2c
    p    points (1/72")   35p,70p

There can be a great deal more to it than just units, however. Note the
following question posed and answered by Eric J. Bohm.

    Eric J. Bohm <[email protected]> wrote:
    !I've got a row of entries packed side by side in a frame.
    !These frames are packed on top of each other.
    !So, when someone deletes a row, the lower ones bubble
    !up automatically.  This works just fine and dandy, and let me
    !extend my thanks to our brave and energetic pTk team.
    !
    !The trick here is what widget do I put this in so that
    !it will be scrollable when I have too many rows to
    !fit on the screen?
      [details and complaints]

 Following up to my own message here.

 All right, after several false leads, I spent 3 hours fighting a canvas
 widget and pounding my head against the canvas.html doc, until I
 finally understood how to include my entries in a frame in a window
 in the canvas and get things to scroll nicely.

 Turns out that the whole thing isn't all that hard to do once I
 understood how canvas widgets work.

 Not sure if its of general interest, but here's the snippet, which was
 stolen from the items demo inside the widget_lib and then brutally
 hacked.

 Perhaps a simpler demo would have been easier to use as a guide, but
 I got there eventually, so my thanks for the widget demo.

    #----------------------------------------
    my $c = $w_frame->Canvas();
    $c->configure(
         -height       => '300',
         -width        => '600',
         -relief       => 'sunken',
         -bd => 2,
     );
     my $w_frame_vscroll = $w_frame->Scrollbar(
                                         -command => ['yview', $c]
                                              );
     my $w_frame_hscroll = $w_frame->Scrollbar(
                                         -orient => 'horiz',
                                         -command => ['xview', $c]
                                               );
     $c->configure(-xscrollcommand => ['set', $w_frame_hscroll]);
     $c->configure(-yscrollcommand => ['set', $w_frame_vscroll]);
     $w_frame_hscroll->pack(-side => 'bottom', -fill => 'x');
     $w_frame_vscroll->pack(-side => 'right', -fill => 'y');
     $c->pack(-expand => 'yes', -fill => 'both',-side=>'top');
     my $entryframe=$c->Frame;
     my $c_win= create $c 'window','0','0',
                          -window=>$entryframe,
                          -anchor=>'nw';
     #----------------------------------------

 Where $c -> configure( -scrollregion => [$top,
 $left, $right, $bottom]) can be used to size things nicely
 once you find out how big it'll be.

 And the widgets you want scrolled should be slaves of $entryframe.

 Vastly more robust than anything I had running in the BLT Table.

 EJB

______________________________________________________________________



10.7. How do I get a Canvas to output PostScript(c)?

Many thanks to Tom Oelke <[email protected]> for providing this
question, answer & snippet of code:

 The following section of code gets the postscript code for the section
 of canvas that's top-left corner is at $min_x, $min_y, and has a
 width and height equivalent to the displayed region. This ps code is
 then piped out to lpr to be printed.

    my $ps = $canvas->postscript( '-x' => $min_x,
                                  '-y' => $min_y,
                                  -width => $canv->Width,
                                 -height => $canv->Height);
    open (PS, "| lpr"); # customize with -Pname e.g.
    print PS $ps;
    close (PS);

Whereas you would use something like:

    open (PS, ">file.ps"); # to output to a file
    print PS $ps;
    close (PS);

______________________________________________________________________



10.8. How do I get a PostScript(c) output of a Canvas w/ widgets?

In general you don't. You can't do it in Tcl/Tk either (if that is any
consolation). Nick Ing-Simmons posted an explicit discussion of what is
involved:


Subj: RE: Canvases and postscript output

On Tue, 28 Nov 95 14:37:09 PST
Davis <[email protected]> writes:
! I have a canvas with text and some entry widgets that I want to create
!postscript from. I used the
!widget->postscript( -file => 'ld.ps', -colormode  => 'gray');
!the file gets created but its empty. Is there some other options I need?

 Core Tk cannot write postscript for embedded windows, the best it
 could do would be to grab a Pixmap of the window as displayed. This
 is fine if the window is visible, but if it is scrolled off screen or under
 another application there is no pixmap.

 Only complete fix is to have a ->postscript method for every
 possible widget which can render un-mapped widgets. This is
 non-trivial task.


!Also I have a scrollbar for this canvas and when I scroll  the entry widget
!actually scroll part way out of the frame the canvas is in. Why does this
!happen and can I fix it?

 The Entry widgets need to be descendants of the canvas or they just
 get clipped to their parent.

______________________________________________________________________



10.9. How do I get the size of a Canvas? After a re-size?

    $canvas->cget(-width);

simply returns the size of the canvas when it was created, whereas

    $canvas->Width;

will get the answer even after a re-size. Substitute [Hh]eight for
[Ww]idth in the above if that is what you want.

Nick Ing-Simmons points out that if you want to have your Canvas be
able to grow to arbitrarily large sizes be sure to specify the -expand or
-fill options when you ->pack the Canvas.

______________________________________________________________________



10.10. How do I bind different actions to different areas of the same
Canvas?

KOBAYASI Hiroaki <[email protected]> recently posted an
extraordinary little script that addresses this question quite succinctly:

 How about this?
 ## I don't know whether this is a good solution or not.
 ## but it works under Tk-b9 + perl5.002b1f.


    #!/usr/local/bin/perl -w
    use Tk;

    ($c = MainWindow->new->Canvas)->
       pack(-fill => 'both', -expand => 1);
    # to survive under Tk-b8.
    # You don't need paren before pack in b9.

    ($pop1 = $c->Menu)->command(-label => "FOO");
    ($pop2 = $c->Menu)->command(-label => "BAR");

    $c->create(oval => 0, 0, 100, 100,
               -fill => 'black',
               -tags => ['popup']);

    $c->Tk::bind($c, '<3>', [\&PopupOnlyThis, $pop1]);
    $c->bind('popup', '<3>', [\&PopupOnlyThis, $pop2]);

    sub PopupOnlyThis {
        print "@_\n";
        my($c, $pop) = @_;

        # to prevent multiple popup.
        Tk->break if defined $Tk::popup;

        my $e = $c->XEvent;
        $pop->Popup($e->X, $e->Y);
        # Tk::Menu::Popup sets $Tk::popup.

    }
    MainLoop;

    $Tk::popup = undef; # to kill warning.

    __END__

______________________________________________________________________



11. Common Problems.

Everything in Tk-land is a reference. When defining callbacks take care to
pass variables by reference. Callbacks are closures and to ensure a variable
gets its current value, as opposed to its value when the callback is defined,
pass by reference, e.g.:

    $frog = 123;
    $b = $mw->Button(
        -text    => 'Push Me',
        -command => [
            sub {
               my($widget, $frog) = @ARG;
               print STDERR "widget=$widget!\n";
               print STDERR "frog=$$frog!\n";
            }, $mw, \$frog,
         ],
    ); # end Button definition

If $frog is not passed by reference the print statement will always
output "123" (actually, the print as it exists will print nothing since it's
trying to dereference $frog, which presumably is now not a reference).
Note that by definition all perl/Tk widgets are already references, since
they're simply Perl objects, and that's why you do not have to print
$$widget!

A good "reference" for handling references and dereferencing are the
perlref(1) and perlobj(1) man pages. A good "reference" for the
various data types you will encounter in this kind of perl programming is
Tom Christiansen's Perl Data Structures Cookbook which is now available
as the perldsc(1) man page.

Also beware the traps that befall perl4 programmers in making the move
to perl 5. References for this include the new perltrap(1) man page as well
as William Middleton's perl425 trap document at:

    http://www.perl.com/perl/all_about/perl425.html
or
    http://w4.lns.cornell.edu/~pvhp/ptk/misc/perl425.html

______________________________________________________________________



11.1. What do the ->, => and :: symbols mean?

The -> is the "infix dereference operator". In other words it is the means
by which one calls a sub with a pass by reference (among other things you
can do with ->). As stated above most things in calls to perl/Tk routines
are passed by reference. The -> is used in perl just as in C or C++. (Most of
the widget primitives are elements of the Tk:: "perl class".) A simple
example of dereferencing would be:

    $x = { def => bar };  # $x is a reference to an anon. hash
    print $x->{def},"\n"; # prints ``bar''

Note that in the case of calling perl/Tk subs there may be more than one
way to call by reference. Compare

    my($top) = MainWindow->new;

with

    my($top) = new MainWindow;

But in general you will be making extensive use of calls like:

    $top -> Widge-type;

There is a clear and succint discussion of references, dereferences, and
even closures in man perlref(1) or see the perl 5 info page at:

    http://www.metronet.com/perlinfo/perl5.html

The use of the => operator is quite common in perl/Tk scripts. Quoting
from man perlop(1):

 The => digraph is simply a synonym for the comma operator. It's
 useful for documenting arguments that come in pairs.

You could say that => is used for aesthetic or organizational reasons. Note
in the following how hard it is to keep track of whether or not every
-option has an argument:

    $query -> Button(-in,\$reply,-side,'left',-padx,2m,-pady,
     2m,-ipadx,2m,-ipady,1m)->pack(-side,'bottom');

As opposed to:

    $query ->Button( -in => \$reply,
                     -side => 'left',
                     -padx => 2m,
                     -pady => 2m,
                     -ipadx => 2m,
                     -ipady => 1m
                    )->pack(-side => 'bottom');

By the way if you wanted the numeric "greater than or equal" you would
use >= not =>.

While the :: symbol can be thought of as similar to the period in a C
struct, it is much more akin to the :: class scope operator in C++:

    a.b.c;       /* something in C */
    a::b::c();   // function in C++
    $a::b::c;    # a scalar in Perl 5
    @a::b::c;    # a list in Perl 5
    %a::b::c;    # an associative array or "hash" in Perl 5
    &a::b::c;    # a function in Perl 5

It is also analogous to the single forward quotation mark in perl 4:

    $main'foo;   # a $foo scalar in perl 4
    $main::foo;  # a $foo scalar in Perl 5

For backward compatibility perl 5 allows you to refer to $main'foo but
$main::foo is recommended.

______________________________________________________________________



11.2. What happened to the ampersands &?

Perl 4 programmers especially may be surprised to find that as of Perl 5.0
the ampersand & may be omitted in a call to a subroutine if the subroutine
has been declared before being used. Actually you can even get around the
declare before omit ampersand rule by using the subs.pm pragma, or by
pre-declaring (without defining) as in a script like:

    #!/usr/bin/perl -w
    use strict;
    use Tk;
    sub Mysub;  #pre-declare allows calling Mysub()

    ...Other main/Tk stuff -
            including call to Mysub() sans &...

    sub Mysub {

        ...Mysub stuff...

    }

Note however that one place the \& reference is sometimes used in perl/Tk
in the setting up a callback for a widget. Other references are possible: e.g.
\$foo is a reference to the scalar variable $foo (this was true even under
perl 4).

______________________________________________________________________



11.3. What happened to the quotation marks?

Perl 4 programmers especially may be surprised to find a serious dearth of
quotation marks around strings in perl 5 scripts such as in perl/Tk. The
"rules have been relaxed" somewhat for the use of quotation marks.
Basically it is OK to leave them out if the context of the string in question
is unambiguous. However, it never hurts to leave them in and may help
readability.

Here is Larry Wall's synopsis of the string situation:

Newsgroups:
   comp.lang.perl.misc
Subject:
   Re: To string or not to string...

In article <[email protected]>,
Andy Finkenstadt <[email protected]> wrote:
! Back when I was learning perl (after receiving a review copy of
! learning perl, and buying the real perl book, each from ORA),
! I always got bit by when I needed to use "strings" and when
! I could get away with bare_words within braces for associative
! arrays.  (Yes, this is under 4.036 if it matters.)
!
! the most typical example would be:
!
! When must I use $assoc{"trailer"} and when can I get away with
! $assoc{trailer}?   Similarly, $ENV{CONTENT_LENGTH} versus
! $ENV{"CONTENT_LENGTH"}?  Unfortunately sometimes my strings
! end up being numbers in their own right, i.e.:  $message{"0"}
! or $msg=0; $message{$msg}.  Which is more appropriate,
! which are merely stylistic, and which are stricly perl5
! features now that I'm upgrading most of my installations
! of perl.

 Perl 4 let you use a "bareword" for a string if it had no other
 interpretation. It would warn you under -w if you used a word
 consisting entirely of lower-case characters, since such a word might
 gain an interpretation someday as a keyword.

 Perl 5 still works the same way, but with several twists.

 1. ) Since you can now call predeclared subroutines as though they
   were builtins, you have to worry about collisions with subroutine
   names too. However...
 2. ) You can completely disallow the default interpretation of
   barewords by saying "use strict subs", which requires any such
   bareword to be a predeclared subroutine. But...
 3. ) Overriding all that, Perl 5 (in recent versions) will FORCE string
   interpretation of any bare identifier used where a single hash
   subscript is expected, either within curlies or before a =>. (Those
   are the places you might usually want the old barewords anyway.)

 The upshot of these rules is that you can write Perl 5 with much less
 punctuation than Perl 4, yet also with less ambiguity. If you so choose.

 Larry

Tcl programmers should note that in Perl the single quotation marks ''
act much as the curly brace {} enclosure does in Tcl (no escaping special
characters $@\ etc.). Whereas the double quotation marks "" allow for
substitution of $variables (the rules are a little different between Tcl
and Perl however).

Note also that a frequently seen short hand in perl5/Tk scripts is the @list
returned by qw():

    @list = qw(zoom schwartz bufigliano);

which is equivalent to:

    @list = split(' ','zoom schwartz bufigliano');

or more simply:

    @list = ('zoom','schwartz','bufigliano');

i.e. the qw/STRING/ @list is not equivalent to the quotation marks
provided by q/STRING/, qq/STRING/, or qq(STRING)...

There are, ironically enough, situations in perl/Tk where one needs to use
quotation marks as in the following by post by
<[email protected]>:


 Paul Wickman wrote in article <[email protected]>:
!
!    Why does the following statement work fine:
!
!$day->pack(-before => $year, -side => 'left');
!
!    But the below generates the given error:
!
!$day->pack(-after => $year, -side => 'left');
!
!Ambiguous use of after => resolved to "after" => at line 191.
!

 Because there is a sub after in scope, probably imported from Tk
 via use Tk;.

 There are two workrounds:

    use Tk qw(MainLoop exit ...); # just ones you use

 or

    $day->pack('-after' => $year, -side => 'left');

______________________________________________________________________



11.4. Must I use "my" on all my variables?

If you use strict; (as recommended) the answer is "probably". This
confines the variables names to your namespace - so your variable does
not conflict with one in the module(s) your are using (you are at the least
useing Tk;). my does "lexical scoping" on a variable rather than the
"dynamic scoping" done by local (like auto variables in C). The
difference between these two is that the scope of my $var is confined to
the block (sub, if, foreach, etc.) in which it is declared and used, as
opposedto local $iable which can propogate to all blocks called by the
block in which it is declared. In general the confined scope of my $var
means that its use will proceed quicker and more efficiently than local
$iable.

If you give a fully qualified variable name such as

    $main::var = 1;  # No "my" needed

Then no my $var is needed. However, the lexical scoping of my $var
makes it preferable.

If you choose to use my (as recommended) then beware that you should
declare a variable my only at the first use (instantiation) of a variable.
Consider yet another way to re-write the "Hello World!" script:

    #!/usr/local/bin/perl -w
    use strict;
    use Tk;
    my $main = new MainWindow;
    my $label = $main->Label(-text => 'Hello World!');
    my $button = $main->Button(-text => 'Quit',
                               -command => sub{exit});
    $label->pack;  #no "my" necessary here
    $button->pack; #or here
    MainLoop;

Considering the finite number of names (in particular the high probability
that a variable named $label or $button was used in one or more of the
extensions to perl that you may be using) it helps one's programming to
use strict; and declare variables yours alone with my.

James M. Stern points out that redundant my declarations are not simply
useless they can be dangerous as in the following script which will not
work:

    #!/usr/local/bin/perl -w
    use strict;
    use Tk;
    my $main = new MainWindow;
    my $label = $main->Label(-text => 'Hello World!');
    my $main;   #WRONG: this $main overrides previous
    my $button = $main->Button(-text => 'Quit', #will now fail
                               -command => sub{exit});
    $label->pack;
    $button->pack;
    MainLoop;

______________________________________________________________________



11.5. Is there a way to find out what is in my perl/Tk "PATH"?

Presuming this question is asking for a little more than the answer you get
when you type:

    ls perl5/lib/Tk/*.pm

there are ways to find out what gets EXPORTED by Tk.pm. Use a script
like:

    #!/usr/bin/perl

    use Tk;
    require 'dumpvar.pl';

    dumpvar('Tk');

or more succintly at the shell command prompt:

    perl -e 'use Tk; require "dumpvar.pl"; dumpvar("Tk");'

The advantage of using dumpvar over ls is that it gives you a brief
summary of all the arguments your widgets want. Note that the output is
many lines and you may wish to pipe through more or less.

If you wish to determine the Configuration options a given widget accepts
(and what the values are at a given point in a script) you may use the
->configure method with no arguments to retrieve the list of lists, as in
this example:

    #!/usr/bin/perl

    use Tk;
    my $main = MainWindow -> new;
    my $scrl = $main -> Scrollbar('-orient' => 'horizontal');

    @scrollconfig = $scrl -> configure;
    for (@scrollconfig) {
        print "@$_\n";
    }

    etc.

Such code is useful for development but is probably best left out,
commented out, or switched out of "production line" code.

______________________________________________________________________



11.6. What is the difference between use and require?

The short answer is that something like:

    use Tk;

is equivalent to:

    BEGIN { require "Tk.pm"; import Tk; }

Hence the essential difference is that a mere require Tk; does not
achieve the import of function/method names. The significance of this is
that it allows one to call ->Button rather than having to call the fully
qualified ->Tk::Button e.g.. For further details on this subject see man
perlmod(1) or see Tom Christiansen's document at:

    ftp://ftp.perl.com/perl/info/everything_to_know/use_vs_require

______________________________________________________________________



11.7. How do I change the cursor/color?

Nick Ing-Simmons <[email protected]> and others posted a series of
answers to this type of question. In summary what they said was:

 Basically

    $mw->configure(-cursor => ... );

 Unless you use one of built-in cursors it gets messy.

 Here copy of what Tk/demos/color_editor does:

    #!/usr/local/bin/perl -w
    use Tk;
    my $mw = MainWindow->new;
    $mw->configure(-cursor => ['@' . Tk->findINC('demos/images/cursor.xbm'),
                                    Tk->findINC('demos/images/cursor.mask'),
                                     'red', 'green']);
    MainLoop;

 That says that argument to -cursor is a list of 4 things:

 1. . Pathname to bitmap with '@' prepended to say it isn't a built in
   name (Using findINC to locate file relative to Tk install location.)
 2. . Pathname to mask bitmap (no @ required)
 3. . Foreground colour
 4. . Background colour


! I want to remap it for the MainWindow
! and will be using a pixmap.

 You won't be using a Pixmap with normal X11. X11 allows *bitmap*
 with optional mask (another bitmap), and two colours.

 The optional nature of the mask means that a simple call with a list
 reference like:

    $mw->configure(-cursor => ['watch', 'red', 'blue']);

 should work alright.

You may also obtain the value of the default cursor for a widget using
something like ->optionGet.

______________________________________________________________________



11.8. How do I ring the bell?

The short answer is

   $widget -> bell;

A slightly longer answer might include a fully functioning script:

    #!/usr/bin/perl
    use Tk;
    $main = MainWindow -> new;
    $butn = $main->Button(-text => 'bell')
    $butn->configure(-command => sub{ $butn->bell; });
    $butn->pack();
    MainLoop;

An even longer answer would be a fully functioning script with a callback:

    #!/usr/bin/perl
    use Tk;
    $main = MainWindow -> new;
    $but = $main->Button(-text => 'bell',
                         -command => sub{ringit($main)})->pack;
    MainLoop;

    sub ringit {
        my $m = shift;
        $m->bell;
    }

Simon Galton <[email protected]> reminds us to be careful in that

 some systems remap this [the "console bell"] to anything from a
 digital sound to a flash on the screen.

______________________________________________________________________



11.9. How do I determine the version of perl/Tk that I am running?

With an up to date perl installation one may query the local perl setup and
all extensions via the command:

    perldoc perllocal

For the Tk extension: version numbering has changed recently and
determining the version of perl/Tk that you are running now depends on
what version you are running:

Tk-b10++:
Tk-b10 (and higher) has changed to $Tk::VERSION (rather than the
older "$Tk:Version") to be consistent with other packages.

Tk-b9.01:
The version numbers as of Tk-b9.01 are stored in the following variables:

    Core Tk version : $Tk::version
    Tk patchLevel :   $Tk::patchLevel
    library :         $Tk::library
    perl/Tk Version : $Tk::Version

At your shell prompt you could say something like the following to
determine you perl/Tk Version:

    perl -e 'use Tk; print "$Tk::Version\n";'

The switch to Tk-b9.01 from previous versions included a large number of
method name changes. Nick was kind enough to include a b9names script
in the distribution that assists with the job of updating your older scripts.
See the b9names script for a rather complete discussion of the name
changes. Geoffroy Ville also posted a notice of some of the changes. Here
is a brief (and very incomplete!) summary:


older                         Tk-b9.01++
packslaves                    pack('slaves')
packpropagate                 pack('propagate')
packForget                    pack('forget')
                              pack('info')

$w->delete if ($w);            $w->destroy if ($w);

Tk-b8(--):
A little script (Tk_module) can tell you and return the value:

    #!/usr/bin/perl
    use Tk;
    local(*Tk_m) = \$Tk::Tk_module;
    print "$Tk_m\n";

Or more succintly say something like the following (at your shell prompt):

    perl -e 'use Tk; print "$Tk::Tk_module\n";'

You can obtain the version of Tk in use with the following (at your shell
prompt):

    perl -e 'use Tk; print "$Tk::tk_version\n";'

where this command returned "4.0" when the previous one (or Tk_module)
returned "b8".

All Tk versions:
Don't forget that you can always determine your Perl version/patchlevel/
etc. with:

    perl -v

(at the shell prompt - it's actually a little harder to get as much
information from within a #!script.) As of perl 5.002 you can use perl -V
to determine your perl Configuration.

OZAWA Sakuro <[email protected]> points out some ways
to do it in a script:

 1. '$]' holds the version number.
 2. In Perl5, 'require NUMBER;' will complain if version is younger
   than NUMBER. (e.g. require 5.001;)
 3. Of course, newly imported (and incompatible) features in newer
   scripts will bailout before execution if parsed by an old interpreter.

Note that if you use English; then $PERL_VERSION holds the version
number.

To determine your MakeMaker version number try something like this
(5.002):

    perl -MExtUtils::MakeMaker -e 'print "$ExtUtils::MakeMaker::VERSION\n";'

or this (5.001m ok):

    perl -e 'use ExtUtils::MakeMaker;print"$ExtUtils::MakeMaker::VERSION\n";'

or even this (older perls and MakeMakers):

    perl -e 'use ExtUtils::MakeMaker;print"$ExtUtils::MakeMaker::Version\n";'

Please note that thoughout this FAQ document there are references to
things like Tk-b10(++) or Tk-b10++ which roughly translated to use
English; means something like "I think this will work with this version
of Tk and (maybe) higher versions...". You might also see Tk-b8(--)
which means something like "it worked with that old version and probably
worked with prior versions and if you are stuck with an old Tk version you
might have to do it this way...".

______________________________________________________________________



11.10. How do I call perl from C?

You need to see a recent copy of the perlembed(1) pod page. By "recent"
it needs to be up to date with at least perl5.002.

Borrowing from Jon Orwant's preamble to that document:

Do you want to:

Use C from Perl?
   Read (at least) the perlcall(1), the perlapi(1), the
   perlxs(1), the perlxstut(1), and the perlguts(1)
   manpages.
Use C++ from Perl?
   Recent changes to MakeMaker will make this easier. Be sure you
   are familiar with the perlcall(1), the perlapi(1), the
   perlxs(1), the perlxstut(1), and the perlguts(1)
   manpages.
Use an executable program from Perl?
   Read about backquotes ``, system(), and exec() built in perl
   functions. Try reading the perlfunc(1) manpage.
Use Perl from Perl?
   Read about do, eval, use and require. The perlfunc(1)
   manpage discusses these. For complete scripts you may also make
   use of the backquotes ``, system(), or exec() built in perl
   functions, but you may take a performance hit in doing so (see
   perlfunc(1) for information).
Use C from C?
   Rethink your design.
Use C++ from C++?
   See previous.
Use Perl from C?
   Read (at least) the perlembed(1) and the perlguts(1)
   manpages.
Use Perl from C++?
   Read (at least) the perlembed(1) and the perlguts(1)
   manpages.

There is also an Doug MacEachern's <[email protected]> embedder's
development kit on CPAN and at a URL of the following form:

    http://www.osf.org/~dougm/perl/Devel-embed-*.tar.gz
or
    http://www.perl.com/cgi-bin/cpan_mod?module=ExtUtils::embed

______________________________________________________________________



11.11. How do I call Tcl code from perl/Tk?

One "official way" to call Tcl from perl/Tk would be via the ->send()
and the ->Receive() methods.

It is also worth noting that you can still have access to a complete Tcl
script from perl via the perl system, or `` (backtick), or even exec
mechanisms. Just be careful with I/O waits and return values if you try one
of these approaches. Further suggestions may be found in the various
perlipc files at:

    ftp://ftp.perl.com/perl/info/everything_to_know/

A more satisfactory Tcl/Tk-wish-like behavior can be embedded in perl
by making appropriate modifications to Dov Grobgeld's perl script that
uses sockets for perl<->wish communication:

#!/usr/local/bin/perl
#####################################################################
#  An example of calling wish as a subshell under Perl and
#  interactively communicating with it through sockets.
#
#  The script is directly based on Gustaf Neumann's perlwafe script.
#
#  Dov Grobgeld [email protected]
#  1993-05-17
#####################################################################

    $wishbin = "/usr/local/bin/wish";

    die "socketpair unsuccessful: $!!\n" unless socketpair(W0,WISH,1,1,0);
    if ($pid=fork) {
            select(WISH); $| = 1;
            select(STDOUT);

        # Create some TCL procedures
            print WISH 'proc echo {s} {puts stdout $s; flush stdout}',"\n";

        # Create the widgets
        print WISH <<TCL;
        # This is a comment "inside" wish

        frame .f -relief raised -border 1 -bg green
        pack append . .f {top fill expand}

        button .f.button-pressme -text "Press me" -command {
            echo "That's nice."
        }
        button .f.button-quit -text quit -command {
            echo "quit"
        }
        pack append .f .f.button-pressme {top fill expand} \\
                       .f.button-quit {top expand}
TCL
        # Here is the main loop which receives and sends commands
        # to wish.
        while (<WISH>) {
            chop;
            print "Wish sais: <$_>\n";
            if (/^quit/) { print WISH "destroy .\n"; last; }
        }
            wait;
    } elsif (defined $pid) {
        open(STDOUT, ">&W0");
        open(STDIN, ">&W0");
        close(W0);
        select(STDOUT); $| = 1;
        exec "$wishbin --";
    } else {
        die "fork error: $!\n";
    }

Ilya Zakharevich <[email protected]> has a "ptcl.h" header file
for the construction of tcl bindings from pTk (there are limitations to this
approach). It was posted to the mailing list archive at:

    http://sun20.ccd.bnl.gov/~ptk/archive/ptk.1995.11/0057.html

If you absolutely must pass large amounts of pre-parsed data between Tcl
and perl then perhaps you should look into Malcolm Beattie's Tcl/Tk
extensions to Perl instead. Those modules are distrubuted at CPAN sites.
As mentioned above running Tcl/Tk/perl is incompatible with running
perl/Tk.

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