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

Esteemed monks,

In my never ending search for more elegant looking and self-documenting code I decided to try out the Switch module. In the following fragment of code: 

#!/usr/local/bin/perl

# AppSys: Manage Profile

use strict;
use CGI qw/:standard/;
use CGI::Carp qw(fatalsToBrowser);
use Switch;

my $cgi = CGI->new;

my $control = 'Search';
switch ( $control ) {
    case ("Search") { 
        print $cgi->header;
        print $cgi->start_html;
        print $cgi->p("Search");
        print $cgi->end_html;
         }
}

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produces the following in the Apache error log: 
[error] syntax error at /home/appsys/www/modperl/ap03.pl line 12, near
+ ") {"
syntax error at /home/appsys/www/modperl/ap03.pl line 14, near "}
}"

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When run as an Apache::Registry script.

When run under mod_cgi (i.e. run from the cgi-bin directory on the same server, it works perfectly and prints 'Search' on the browser.

I will ask this on the mod_perl list also, but I have had some good assistance here for mod_perl type questions, so maybe someone can help.

jdtoronto

Replies are listed 'Best First'.
Re: Switch (module) and Apache::Registry problem.
by diotalevi (Canon) on Oct 30, 2003 at 16:27 UTC

    While I don't know the answer I suspect it is because Switch is actually a source filter and it probably isn't generated correct perl for the mod_perl environment. In fact, I quote from the module's documentation.

    BUGSThere are undoubtedly serious bugs lurking somewhere in code this funky :-) Bug reports and other feedback are most welcome.
    I'd almost rather just point you towards something else besides Switch if only because you're introducing such oddball code that I couldn't help but laugh when I read your introductory sentence.

[reply]
Re: Switch (module) and Apache::Registry problem.
by nevyn (Monk) on Oct 30, 2003 at 17:36 UTC

    Well if you really like the look of the switch type construct, TIMTOWTDI...

    SubSwitch.pm

    package SubSwitch;
use strict;

use base 'Exporter';
 
our @EXPORT_OK = qw(
   switch
   case
);
 
our $SubSwitch = undef;
 
sub switch
{
        my ($val, $func) = @_;
 
        local $SubSwitch = $val;
 
        $func->();
}
sub case
{
        my ($val, $func) = @_;
 
        if ($val ne $SubSwitch) { return; }
 
        $func->();
}
 
1;

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    test.pl

    #! /usr/bin/perl -w
 
use strict;
 
use SubSwitch qw(switch case);
 
switch ("foo", sub {
        case ("bar", sub {
                print "not here\n";
        });
        case ("foo", sub {
                print "here\n";
                switch ("bar", sub {
                        case ("bar", sub {
                                print "there\n";
                        });
                });
        });
        case ("bar", sub {
                print "still not here\n";
        });
})

    [download]
    --
    James Antill
[reply]
[d/l]
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Re: Switch (module) and Apache::Registry problem.
by hardburn (Abbot) on Oct 30, 2003 at 16:30 UTC

    Yeah, Switch is really cool. Don't use it.

    ----
    I wanted to explore how Perl's closures can be manipulated, and ended up creating an object system by accident.
    -- Schemer

    : () { :|:& };:

    Note: All code is untested, unless otherwise stated

[reply]
[d/l]
      Okay, so switch is too cool for its own good eh :)

      Thanks guys, now I can go back to my ugly old nested if's and not feel guilty! I always liked the switch/case construct in EBasic back in the CP/M - MP/M days, and then in C of course, always wanted one in Perl - I suppose I have to wait for Perl 6 for given/when.

      jdtoronto

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        Not all is lost for Perl5. A hash containing subroutine refs can be equally readable, though fall-through can be difficult to achieve. It also has the advantage of having O(1) efficiency, just like switches in C (an interesting discussion of which is here).

        In C switches, you trade off some flexibility for efficiency. Perl6 switches will allow any expression to be used as a case, so they're basically as efficient as a bunch of if/elsif statements (though I'm hoping simple cases will be optimized into something like a C switch).

        ----
        I wanted to explore how Perl's closures can be manipulated, and ended up creating an object system by accident.
        -- Schemer

        : () { :|:& };:

        Note: All code is untested, unless otherwise stated

[reply]
[d/l]

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