Actually, bobn is not right in this case. Your "case 2" is very close to the mark -- the right way would be: 
my $change_mode = \&change_mode;
...
# Case 2:  Callback routine called with argument (corrected):
# given that $change_mode is a ref to a sub
$main->Button(-text => 'To Upper Case',
              -command => [ $change_mode, 2 ]
              )->pack;

[download]
The "-command" option on Tk widgets (like the "bind" method) can accept an array ref (anonymous in this case), in which the first element of the array is the subroutine reference, and the remaining elements are args to pass to the sub.

The "bind" case is a little different, because the sub will actually get the widget handle that invoked it as the first arg every time a "bound" event triggers the sub, whereas the "-command" option does not pass the widget handle as the first arg.

In reply to Re: Re: Re: Passing arguments to callback routines with named references by graff
in thread Passing arguments to callback routines with named references by nysus

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.