func damm(digits) {
    static tbl = [
          [0, 3, 1, 7, 5, 9, 8, 6, 4, 2],
          [7, 0, 9, 2, 1, 5, 4, 8, 6, 3],
          [4, 2, 0, 6, 8, 7, 1, 3, 5, 9],
          [1, 7, 5, 0, 9, 8, 3, 4, 2, 6],
          [6, 1, 2, 3, 0, 4, 5, 9, 7, 8],
          [3, 6, 7, 4, 2, 0, 9, 5, 8, 1],
          [5, 8, 6, 9, 7, 2, 0, 1, 3, 4],
          [8, 9, 4, 5, 3, 6, 2, 0, 1, 7],
          [9, 4, 3, 8, 6, 1, 7, 2, 0, 5],
          [2, 5, 8, 1, 4, 3, 6, 7, 9, 0],
    ]

    !digits.flip.reduce({|row,col| tbl[row][col] }, 0)
}

for n in [5724, 5727, 112946] {
    say "#{n}:\tChecksum digit #{ damm(n.digits) ? '' : 'in'}correct."
}