sub mapfirst {
    my( $sub )= shift( @_ );
    &$sub( map { $_->[0] } @_ );
#          ^^^^^^^^^^^^^^^^^^ Here is the selection code
}
my @a= ( 1..3 );
my @b= ( 4..6 );
my @c= ( 7..9 );
sub addten { $_ += 10  for @_ }
mapfirst( \&addten, \@a, \@b, \@c );
mapfirst( sub { print "@_\n" }, \@a, \@b, \@c );

##</code><code>##

    if( 0 == @_ ) {
        &$sub();
    } elsif( 1 == @_ ) {
        &$sub( $_[0][0] );
    } elsif( 2 == @_ ) {
        &$sub( $_[0][0], $_[1][0] );
    } elsif( 3 == @_ ) {
        &$sub( $_[0][0], $_[1][0], $_[2][0] );
    # etc to some arbitrary maximum number of arguments
    }

##</code><code>##

    eval "&\$sub( " . join( ", ", map "\$_[$_][0]", 0..$#_ ) . " )"

##</code><code>##

    $av= sub { \@_ }->( @$av, $_->[0] )   for  @_;

##</code><code>##

sub mapfirst {
    my( $sub )= shift( @_ );

    my $av= [];
    $av= sub { \@_ }->( @$av, $_->[0] )   for  @_;
    &$sub( @$av );

    ## &$sub( map { $_->[0] } @_ );
}
my @a= ( 1..3 );
my @b= ( 4..6 );
my @c= ( 7..9 );
sub addten { $_ += 10  for @_ }
mapfirst( \&addten, \@a, \@b, \@c );
mapfirst( sub { print "@_\n" }, \@a, \@b, \@c );

##</code><code>##

    ( $x, $y )= ( $y, $x );

##</code><code>##

sub swapPairs { @_[ map $_^1, 0..$#_ ]= @_ }

##</code><code>##

    $_= $something  for @_;

##</code><code>##

use Algoritm::Loops 'MapCarE';
sub swapValues { MapCarE { $_[0]= $_[1] } \@_, [reverse @_] }