Start
  prog
    Nodes[Nstmt]
      stmt_assign
        id@(1:1-1:2)='x'
        '='@(1:3-1:4)
        expr
          id@(1:5-1:6)='y'
        ';'@(1:6-1:7)
      stmt_while
        'while'@(2:1-2:6)
        '('@(2:7-2:8)
        expr
          id@(2:8-2:9)='z'
        ')'@(2:9-2:10)
        '{'@(2:11-2:12)
        Nodes[Nstmt]
          stmt_print
            'print'@(2:13-2:18)
            '('@(2:18-2:19)
            expr
              id@(2:19-2:20)='t'
            ')'@(2:20-2:21)
            ';'@(2:21-2:22)
          stmt_assign
            id@(2:23-2:24)='k'
            '='@(2:24-2:25)
            expr
              id@(2:25-2:26)='u'
            ';'@(2:26-2:27)
        '}'@(2:28-2:29)
  Eof@(3:1-3:1)=''