Re: How to build a real multi-level dispatch table

[George_Sherston]

I've been following this thread with some interest, as I just finished writing a CGI with a very unwieldy set of if / elsif / else statements, and I'm interested in how to put it on a more rational footing (posted below for anyone who wants a laugh). In simpler situations I've used a dispatch table. But here I couldn't work out how to pass (the right) arguments. As far as I can see, this is not handled explicitly above. I'd be interested in how to deal with the need (A) to pass different arguments to different subs; and (B)to pass different args to the *same* sub under different conditions ?

My baobab-style if tree, so we can all see what I'm up against:

    if ($g{'Action'} eq 'MainPage') {
        MainPage($Persist, $UserName);
    }
    if (($g{'Action'} eq 'Course') or ($g{'Action'} eq 'EditCourse')) 
+{
        $g{'CourseID'} = GetNewCourse() unless defined $g{'CourseID'};
        UpdateTempData($g{'CourseID'});
        EditCourse($Persist, $g{'CourseID'}, $g{'Return'});
    }
    elsif ($g{'Action'} eq 'Create Course') {
        my $CourseID = GetNewCourse($UserName);
        UpdateTempData($CourseID);
        EditCourse($Persist, $CourseID, $g{'Return'});
    }
    elsif ($g{'Action'} eq 'EditEvent') {
        EditEvent($Persist, $g{'CourseID'}, $g{'Return'});
    }
    elsif ($g{'Action'} eq 'New Venue') {
        my $VenueID = GetNewVenue($Persist,$UserName);
        EditVenue($Persist, $VenueID, $g{'Return'});
    }
    elsif (($g{'Action'} eq 'Venue') or ($g{'Action'} eq 'EditVenue'))
+ {
        EditVenue($Persist, $g{'VenueID'}, $g{'Return'});
    }
    elsif ($g{'Action'} eq 'Course Overview') {
        CourseView($Persist, $UserName);
    }
    elsif ($g{'Action'} eq 'Venue Overview') {
        VenueView($Persist,$UserName);
    }
    elsif ($g{'Action'} eq 'DeleteCourse') {
        DeleteCourse($Persist, $g{'CourseID'}, $g{'Return'});
    }
    elsif ($g{'Action'} eq 'Delete Course') {
        DeleteCourseYes($Persist, $g{'CourseID'}, $g{'Return'});
        if ($g{'Return'} eq 'CourseView') {
            CourseView($Persist, $UserName);
        }
        else {
            MainPage($Persist, $UserName);
        }
    }
    elsif ($g{'Action'} eq 'Keep Course') {
        if ($g{'Return'} eq 'CourseView') {
            CourseView($Persist, $UserName);
        }
        else {
            MainPage($Persist, $UserName);
        }
    }
    elsif ($g{'Action'} eq 'DeleteEvent') {
        DeleteEvent( $Persist, $g{'EventID'}, $g{'Return'});
    }
    elsif ($g{'Action'} eq 'Delete Event') {
        DeleteEventYes( $Persist, $g{'EventID'});
        if ($g{'Return'} eq 'CourseView') {
            CourseView($Persist, $UserName);
        }
        elsif ($g{'Return'} eq 'EditEvent') {
            EditEvent($Persist, $g{'CourseID'},0,$g{'CourseTitle'});
        }
        else {
            MainPage($Persist, $UserName);
        }
    }
    elsif ($g{'Action'} eq 'Keep Event') {
        if ($g{'Return'} eq 'CourseView') {
            CourseView($Persist, $UserName);
        }
        elsif ($g{'Return'} eq 'EditEvent') {
            EditEvent($Persist, $g{'CourseID'},0,$g{'CourseTitle'});
        }
        else {
            MainPage($Persist, $UserName);
        }
    }
    elsif ($g{'Action'} eq 'DeleteVenue') {
        DeleteVenue($Persist, $g{'VenueID'}, $g{'Return'});
    }
    elsif ($g{'Action'} eq 'Delete Venue') {
        DeleteVenueYes($Persist, $g{'VenueID'}, $g{'Return'});
        if ($g{'Return'} eq 'VenueView') {
            VenueView($Persist, $UserName);
        }
        else {
            MainPage($Persist, $UserName);
        }
    }
    elsif ($g{'Action'} eq 'Keep Venue') {
        if ($g{'Return'} eq 'VenueView') {
            VenueView($Persist, $UserName);
        }
        else {
            MainPage($Persist, $UserName);
        }
    }
    elsif ($g{'Action'} eq 'Save Venue') {
        if (my $Errors = SaveVenue($Persist, $UserName)) {
            EditVenue($Persist, $g{'VenueID'}, $g{'Return'}, $Errors);
        }
        else {
            WriteVenue();
            if ($g{'Return'} eq 'ReturnToEditEvent') {
                SaveVenue($Persist, $UserName);
                EditEvent($Persist, $g{'CourseID'}, $g{'Return'},$g{'C
+ourseTitle'},0);
            }
            elsif ($g{'Return'} eq 'VenueView') {
                SaveVenue($Persist, $UserName);
                VenueView($Persist, $UserName);
            }
            else {
                SaveVenue($Persist, $UserName);
                MainPage($Persist, $UserName);
            }
        }
    }
    elsif ($g{'Action'} eq 'More Keywords') {
        EditCourse($Persist, $g{'CourseID'}, $g{'Return'});
    }
    elsif ($g{'Action'} eq 'Next Step') {
        if (my @Errors = CourseErrorCheck()) {
            EditCourse($Persist, $g{'CourseID'}, $g{'Return'}, \@Error
+s);
        }
        elsif (my $OldTitle = TitleCheck()) {
            UpdateTempData($g{'CourseID'});
            QueryTitle($Persist, $g{'CourseID'}, $g{'Return'}, $OldTit
+le);
        }
        else {
            UpdateTempData($g{'CourseID'});
            EditCourseInfo($Persist, $g{'CourseID'}, $g{'Return'});
        }
    }
    elsif ($g{'Action'} eq 'New Course') {
        my $g = GetFromFile($g{'CourseID'},\%g);
        %g = %$g;
        DestroyTempFile($g{'CourseID'});
        $g{'CourseID'} = GetNewCourse();        
        MakeTempFile($g{'CourseID'});
        UpdateTempData($g{'CourseID'});
        EditCourseInfo($Persist, $g{'CourseID'}, $g{'Return'});
    }
    elsif ($g{'Action'} eq 'Change Name') {
        UpdateTempData($g{'CourseID'});
        EditCourseInfo($Persist, $g{'CourseID'}, $g{'Return'});
    }
    elsif ($g{'Action'} eq 'More Links') {
        UpdateTempData($g{'CourseID'});
        EditCourseInfo($Persist, $g{'CourseID'}, $g{'Return'});
    }
    elsif ($g{'Action'} eq 'Another Page') {
        SaveUserPage($Persist, $g{'CourseID'},$g{'PageTitle'},$g{'Page
+Text'},$g{'WeFormat'},$g{'CurrentPage'});
        $g{'PageTitle'} = undef;
        $g{'PageText'} = undef;
        EditCourseInfo($Persist, $g{'CourseID'}, $g{'Return'},0,1);
    }
    elsif ($g{'Action'} =~ /^Edit Page (\d*)$/) {
        SaveUserPage($Persist, $g{'CourseID'},$g{'PageTitle'},$g{'Page
+Text'},$g{'WeFormat'},$g{'CurrentPage'});
        EditCourseInfo($Persist, $g{'CourseID'}, $g{'Return'}, $g{"Pag
+eID_$1"},1);
    }
    elsif ($g{'Action'} =~ /^Delete Page (\d*)$/) {
        UpdateTempData($g{'CourseID'});
        SaveUserPage($Persist, $g{'CourseID'},$g{'PageTitle'},$g{'Page
+Text'},$g{'WeFormat'},$g{'CurrentPage'});
        QueryDeleteUserPage($Persist, $g{'CourseID'}, $g{'Return'},$g{
+"PageID_$1"},$g{'CurrentPage'});
    }
    elsif ($g{'Action'} eq 'Yes, Delete Page') {
        DeleteUserPage($g{'PageID'});
        UpdateTempData($g{'CourseID'});
        EditCourseInfo($Persist, $g{'CourseID'}, $g{'Return'},$g{'Curr
+entPage'},1);
    }
    elsif ($g{'Action'} eq 'No, Keep Page') {
        UpdateTempData($g{'CourseID'});
        EditCourseInfo($Persist, $g{'CourseID'}, $g{'Return'},$g{'Curr
+entPage'},1);
    }
    elsif ($g{'Action'} eq 'No, Keep Page') {
        UpdateTempData($g{'CourseID'});
        EditCourseInfo($Persist, $g{'CourseID'}, $g{'Return'},$g{'Curr
+entPage'},1);
    }
    elsif ($g{'Action'} eq 'Proceed') {
        SaveUserPage($Persist, $g{'CourseID'},$g{'PageTitle'},$g{'Page
+Text'},$g{'WeFormat'},$g{'CurrentPage'});
        UpdateTempData($g{'CourseID'});
        if (my $TearSheetError = CourseInfoErrorCheck()) {
            EditCourseInfo($Persist, $g{'CourseID'}, $g{'Return'},0,0,
+$TearSheetError);
        }
        else {
            EditEvent($Persist, $g{'CourseID'}, $g{'Return'},$g{'Cours
+eTitle'},0);
        }
    }
    elsif ($g{'Action'} eq 'Save Course') {
        SaveUserPage($Persist, $g{'CourseID'},$g{'PageTitle'},$g{'Page
+Text'},$g{'WeFormat'},$g{'CurrentPage'});
        UpdateTempData($g{'CourseID'});
        if (my $TearSheetError = CourseInfoErrorCheck()) {
            EditCourseInfo($Persist, $g{'CourseID'}, $g{'Return'},0,0,
+$TearSheetError);
        }
        else {
            SaveCourse($Persist, $g{'CourseID'}, $g{'Return'});
            if ($g{'Return'} eq 'CourseView') {
                CourseView($Persist, $UserName);
            }
            else {
                MainPage($Persist, $UserName);
            }
        }
    }
    elsif ($g{'Action'} eq 'Make Venue') {
        my $VenueID = GetNewVenue($Persist,$UserName);
        EditVenue($Persist, $VenueID,'ReturnToEditEvent',0,$g{'CourseI
+D'},$g{'CourseTitle'});
    }
    elsif ($g{'Action'} eq 'Add Event') {
        if (my $Errors = CheckEvent($g{'CourseID'})) {
            EditEvent($Persist, $g{'CourseID'}, $g{'Return'},$g{'Cours
+eTitle'},$Errors);
        }
        else {
            AddEvent($Persist, $g{'CourseID'}, $g{'CourseTitle'});
            EditEvent($Persist, $g{'CourseID'}, $g{'Return'},$g{'Cours
+eTitle'},0);
        }
    }
    elsif ($g{'Action'} eq 'Save All') {
        my $Errors = CheckEvent($g{'CourseID'});
        my $DateError = 0;
        my $VenueError = 0;
        my $DuplicateError = 0;
        if ($Errors) {
            $DateError = 1 if grep {$_ eq 'Date'} @$Errors;
            $VenueError = 1 if grep {$_ eq 'Venue'} @$Errors;
            $DuplicateError = 1 if grep {$_ eq 'Duplicate'} @$Errors;
        }
        if ($DateError + $VenueError == 1) {
            EditEvent($Persist, $g{'CourseID'}, $g{'Return'},$g{'Cours
+eTitle'},$Errors);
        }
        else {
            AddEvent($Persist, $g{'CourseID'}, $g{'CourseTitle'}) unle
+ss ($DuplicateError == 1 or $DateError + $VenueError == 2);
            if (stat "$filepath/tempfiles/$g{'CourseID'}") {
                UpdateTempData($g{'CourseID'});
                SaveCourse($Persist, $g{'CourseID'}, $g{'Return'});
            }
            if (defined $g{'Return'} and $g{'Return'} eq 'CourseView')
+ {
                    CourseView($Persist, $UserName);
            }
            else {
                MainPage($Persist, $UserName);
            }
        }
    }
    else {
        MainPage($Persist, $UserName, $UserCookie);
    }

§ George Sherston

[tye]

That is what closures are for:

my %actions= (
    MainPage => sub { MainPage( $Persis, $UserName ) },
    Course => sub {
        EditCourse(
            $Persist,
            def(\$g{CourseID},sub{GetNewCourse()}),
            $g{Return} )
    },
    EditCourse => 'Course',
    'Create Course' => sub {
        EditCourse( $Persist, GetNewCourse($UserName), $g{Return} )
    },
    EditEvent => sub {
        EditEvent( $Persist, $g{CourseID}, $g{Return} )
    },
    'New Venue' => sub {
        EditVenue(
            $Persist,
            GetNewVenue($Persist,$UserName),
            $g{Return} )
    },
    Venue => sub {
        EditVenue( $Persist, $g{'VenueID'}, $g{'Return'} )
    },
    EditVenue => 'Venue',
    'Delete Course' => \&DeleteCoursePage,
    'Keep Course' => sub {
        if ($g{'Return'} eq 'CourseView') {
            CourseView($Persist, $UserName);
        }
        else {
            MainPage($Persist, $UserName);
        }
    },
    # ...
);
# ...
my $action= $actions{ $g{Action} };
if(  ! $action  ) {
    MainPage( $Persist, $UserName, $UserCookie );
} else {
    $action= $actions{$action}   if  ! ref($action);
    $action->();
}

where you add more subroutines as needed to keep the hash declaration from being too complex.
        - tye (but my friends call me "Tye")