print join ",", map { &{$field_info{$_}{format}}($deal) } @fields;
##</code><code>##

#!/usr/bin/perl -w

use strict;

#I am sure there are more fields than this
my @fields = qw(a b);

#Subroutines that return a value.  I imagine
#you had alot more processing in here, but
#this is all make-believe =)
my %field_info = (
  a => { format => sub {return $_[0]->{deep}{inside}{a}} },
  b => { format => sub {return $_[0]->{deep}{inside}{b}} },
);

#Had to simulate a reasonable amount of data, that could
#potentially cause a slowdown

#Let's make @ deals
my @deals;
for(my $i = 0; $i < 10000; $i++) {
  push @deals, { deep => { inside => { a => "a[$i]", b => "b[$i]"} } };
}

#Force commas to be the field seperator inside 
#print(), so we can drop the join(), and pass an array
#to print, rather than one long "joined" string - it should be faster
local $, = ',';

#Set the output record seperator, so that each call to
#print tags on a "\n" after printing out the $deal
local $\ = "\n";

#Dereference the subroutines, so that we aren't doing a hash traversal
#each time through the @deals loop AND the map.
my @dereferenced_subs = map { $_->{format} } @field_info{ @fields };

#Print out each $deal
foreach my $deal (@deals) {
  print map { $_->($deal) } @dereferenced_subs;
}