my %h = (
  func1 => sub { return sprintf ("0x%x", shift) },
  func2 => sub { return sprintf ("%b", shift) },
  func3 => sub { return sprintf ("%d", shift) },
);

##</code><code>##

$h{func1}->();

##</code><code>##

my %h = (
  func1 => sub { 
    my $value = shift @_;
    return sprintf ("0x%x", $value) 
  },
  func2 => sub { 
    my $value = shift @_;
    return sprintf ("%b", $value); 
},
  func3 => sub { 
    my $value = shift @_;
    return sprintf ("%d", $value); 
},
);

##</code><code>##

sub foo {
  # requires an even number of parameters in @_
  my %params = @_; 
  return;
}

# to call:

foo(qw/key1 val1 key2 val2 key3 val3/);

##</code><code>##

sub foo {
  # get singular hash reference with any number of key/value pairs
  my $params = shift @_; # or alternatively, my $params = $_[0]
  
  # some may want to dereference (I usually don't)

  my %params = %$params;

  return;
}

# to call:

foo( {'key1' => 'val1', 'key2' => 'val2', 'key3' => 'val3' });

# or without braces,

foo( 'key1' => 'val1',  'key2' => 'val2', 'key3' => 'val3' );