package Foo;
sub new
{
  my($pkg, %args) = @_;
  my $self =
  {
    method => 'correlation',
    %args
  };

  $self->{funcs}{correlation} = \&$self->correlation;

  return bless $self, $pkg;
}

sub correlation
{
  print "This is the correlation function!";
}

##</code><code>##

  my $x = new Foo(method => 'biscuit');

##</code><code>##

  if exists $self->{funcs}{$self->{method}}
  {
    $self->{funcs}{$self->{method}}(params);
  }
  else
  {
    die "Sorry, the method $self->{method} isn't valid!";
  }

##</code><code>##

  #This says "Not a CODE referece at Foo.pm line..."
  $self->{funcs}{correlation} = \&$self->correlation;

  #This says "Can't call method 'correlation' on unblessed
  # reference at Foo.pm line..."
  $self->{funcs}{correlation} = \&{$self->correlation};

  #And this says "Scalar found where operator expected at
  # Foo.pm line...
  $self->{funcs}{correlation} = \&($self->correlation);