# -*- mode: cperl6; -*-

# 2011 Perl 6 Coding Contest
# Edgar Gonzàlez i Pellicer

# Multisets
module Multiset;


# Take a n-multiset
# Recursive helper function
sub multisets-rec(Array $src, Int $n, Int $i, Array $cur) {
  # No more?
  if $n == 0 {
    # Add it
    take [ $cur.clone ];
  }
  else {
    # For each one
    for $i ..^ $src.elems -> $j {
      # Add it to current
      $cur.push($src[$j]);

      # Recurse from there
      multisets-rec($src, $n - 1, $j, $cur);

      # Remove
      $cur.pop;
    }
  }
}


# Generate all n-multisets
sub multisets(Array $src, Int $n) is export {
  return gather {
    # Recurse
    multisets-rec($src, $n, 0, []);
  }
}