Pong in SDL

drose2211 has asked for the wisdom of the Perl Monks concerning the following question:

Hello. I am a complete beginner with Perl and code in general. I was reading the SDL manual and going through the section on how to make Pong. I decided to write each section for myself and try to understand what was happening in each section I ran into a problem in the area where a subroutine is used to render the ball and paddles to the screen. I typed it as shown in the manual but am getting a syntax error at (> . Sorry if this is a stupid question

 
$app-add_show_handler (>
    sub {
        $app->draw_rect( [ 0, 0, $app->w, $app->h ], 0x000000FF );
        $app->draw_rect( $ball->{rect}, 0xFF0000FF );
        $app->draw_rect( $player1->{paddle}, 0xFF0000FF );
        $app->draw_rect( $player2->{paddle}, 0xFF0000FF );
        $app->update;
      }
    );
[download]

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Re: Pong in SDL by roboticus (Chancellor) on Nov 30, 2017 at 16:55 UTC
drose2211: I've not used SDL, and you don't provide enough context for me to be sure. But looking at just the bit of code you presented, I'd guess one of: Perhaps you meant `$app_add_show_handler`?, Or maybe A previous line isn't complete and perl detected the syntax error here instead of a few lines earlier? I then took a look at the cpan page for SDL and noticed the link to the book. A quick search for add_show_handler finds that exact bit of code (sans comments) on page 52. I thought you were using the '>' to indicate the location of the syntax error, but in fact the book shows a '>' symbol there. I expect that's a syntax error right there. Looking around in the text, I'm thinking they made a transposition error and it should be: `$app->add_show_handler(` [download] Where the '>' at the end of the line should be moved left. If so, then they've made the same mistake on page 56 (and possibly elsewhere). Update: Tweaked the first line to make it read better. ...roboticus When your only tool is a hammer, all problems look like your thumb.	[reply] [d/l] [select]
Re^2: Pong in SDL by choroba (Cardinal) on Nov 30, 2017 at 22:41 UTC
That's probably because the pod `C<$app->add_show_handler(>` [download] renders as `$app-add_show_handler(>` [download] and should be written correctly as `C<< $app->add_show_handler( >>` [download] ($q=q:Sq=~/;[c](.)(.)/;chr(-\|\|-\|5+lengthSq)`"S\|oS2"`map{chr \|+ord }map{substrSq`S_+\|`\|}3E\|-\|`7**2-3:)=~y+S\|`+$1,++print+eval$q,q,a, [download]	[reply] [d/l] [select]
Re^2: Pong in SDL by drose2211 (Sexton) on Dec 01, 2017 at 00:01 UTC
You were correct. The '>' was causing the syntax error. It needed to be written as $app->add_show_handler instead and that fixed the problem. Thanks for the help!	[reply]