pairs.rs

macro_rules! pairs{
  () => {};
  ($h : expr, $($t : expr,)*) =>
  {
      println!("({},{})", $h, $h);
      $(println!("({},{})", $h, $t);)*
      $(println!("({},{})", $t, $h);)*
      pairs!{$($t,)*}
  }
}

macro_rules! pairs{
  ({} { $($r: expr),* }) => {};
  ({$lh : expr, $($lt : expr,)*} { $($r: expr),* }) =>
  {
       $(println!("({},{})", $lh, $r);)*
       pairs!{{$($lt,)*} {$($r),*}}
  }
}