Inspired by having recently worked my way through Aristotle's nice article on the Y Combinator in Perl, I wondered if Howto avoid large hard-coded else-if function calls could be done using a similar technique. I eventually got it to go, but only by moving to 5.8.8 (rather than 5.8.6) and applying some hacks to work around (further) limitations of the List::Util::reduce() operator.

In the following code, the list of functions to be applied are built up (curried?) together to produce a single code ref that can be applied to the inputs and produce the outputs in a single pass (kinda):

#! perl -slw
require 5.8.8;
use strict;
use List::Util qw[ reduce ]; $a = $b;

my %dispatch = (
    A => sub{ map{ $_ +1 } @_ },
    B => sub{ map{ $_ *2 } @_ },
    C => sub{ map{ $_**2 } @_ },
    D => sub{ map{ $_ +3 } @_ },
    E => sub{ map{ $_ *5 } @_ },
);

my $func_com = $ARGV[ 0 ] || 'ABC';
my @some_val = 1 .. 10;

my $combo = reduce{
    { ## 1 
        my( $x, $y ) = ( $a, $b ); ## 3
        $a = sub{ $y->( $x->( @_ ) ) }
    } ## 2 
} map{
    $dispatch{ $_ }||sub{ @_ }
} split '', $func_com;

printf "[ %s ]", join ',', $combo->( @some_val );

__END__
c:\test>\AS817\perl\bin\perl5.8.8.exe junk6.pl ABCDE
[ 95,195,335,515,735,995,1295,1635,2015,2435 ]
[download]

The hacks (this doesn't work before 5.8.8 because of closure bugs with reduce() that got recently fixed):

1. (## 1 & ## 2) It doesn't work unless I nest a bare block inside the er, bare block passed to reduce().

   Shouldn't the outer bare block be sufficient to form the closures?

2. (## 3) It also doesn't work unless I assign the globals $a & $b to lexicals.

   It's perfectly possible to close over package globals in other instances, so is this a bug?

   Or is it the alias nature of $a & $b that prevents the closure working correctly?

Both hacks are still required of 5.8.9 5.9.x (circa a month or so ago), so are either or both worth raising a perlbug over?