Java + Antlr，树深度

Question

我正在使用antlr库来开发Pascal到C的翻译器。其中一个功能应该是解析器输出树的可视化，类似于Eclipse插件生成的：

eclipse plugin tree

我已经取得的成就是：

my graphviz tree

正如您所看到的，使用GraphViz工具生成的树是平的。以下是我用于测试的示例pascal代码：

program DataFiles;

type
   StudentRecord = record
      Number: Integer;
      Name: String;
   end;

var
   Student: StudentRecord;
   f: file of StudentRecord;

begin
   Assign(f  , 'MyFiledat');
   Rewrite(f);
   Student.Number := 12345;
   Student.Name := 'John Smith';
   Write(f , Student);
   Close(f);
end.

Java代码：

Core core = Core.getInstance();
String hello = core.readFile(new File("test/test_sources/Program1.p"));

CharStream stream = 
    new ANTLRStringStream(hello);
PascalTreeLexer lexer = new PascalTreeLexer(stream);
TokenStream tokenStream = new CommonTokenStream(lexer);
PascalTreeParser parser = new PascalTreeParser(tokenStream);

CommonTree tree = (CommonTree) parser.program().getTree();
DOTTreeGenerator gen = new DOTTreeGenerator();
StringTemplate st = gen.toDOT(tree);

System.out.println(st);

最后，DOTTree：

digraph {

    ordering=out;
    ranksep=.4;
    bgcolor="lightgrey"; node [shape=box, fixedsize=false, fontsize=12, fontname="Helvetica-bold", fontcolor="blue"
        width=.25, height=.25, color="black", fillcolor="white", style="filled, solid, bold"];
    edge [arrowsize=.5, color="black", style="bold"]

  n0 [label=""];
  n1 [label="program"];
  n2 [label="DataFiles"];
  n3 [label=";"];
  n4 [label="type"];
  n5 [label="StudentRecord"];
  n6 [label="="];
  n7 [label="record"];
  n8 [label="Number"];
  n9 [label=":"];
  n10 [label="Integer"];
  n11 [label=";"];
  n12 [label="Name"];
  n13 [label=":"];
  n14 [label="String"];
  n15 [label=";"];
  n16 [label="end"];
  n17 [label=";"];
  n18 [label="var"];
  n19 [label="Student"];
  n20 [label=":"];
  n21 [label="StudentRecord"];
  n22 [label=";"];
  n23 [label="f"];
  n24 [label=":"];
  n25 [label="file"];
  n26 [label="of"];
  n27 [label="StudentRecord"];
  n28 [label=";"];
  n29 [label="begin"];
  n30 [label="Assign"];
  n31 [label="("];
  n32 [label="f"];
  n33 [label=","];
  n34 [label="'MyFiledat'"];
  n35 [label=")"];
  n36 [label=";"];
  n37 [label="Rewrite"];
  n38 [label="("];
  n39 [label="f"];
  n40 [label=")"];
  n41 [label=";"];
  n42 [label="Student"];
  n43 [label="."];
  n44 [label="Number"];
  n45 [label=":="];
  n46 [label="12345"];
  n47 [label=";"];
  n48 [label="Student"];
  n49 [label="."];
  n50 [label="Name"];
  n51 [label=":="];
  n52 [label="'John Smith'"];
  n53 [label=";"];
  n54 [label="Write"];
  n55 [label="("];
  n56 [label="f"];
  n57 [label=","];
  n58 [label="Student"];
  n59 [label=")"];
  n60 [label=";"];
  n61 [label="Close"];
  n62 [label="("];
  n63 [label="f"];
  n64 [label=")"];
  n65 [label=";"];
  n66 [label="end"];
  n67 [label="."];

  n0 -> n1 // "" -> "program"
  n0 -> n2 // "" -> "DataFiles"
  n0 -> n3 // "" -> ";"
  n0 -> n4 // "" -> "type"
  n0 -> n5 // "" -> "StudentRecord"
  n0 -> n6 // "" -> "="
  n0 -> n7 // "" -> "record"
  n0 -> n8 // "" -> "Number"
  n0 -> n9 // "" -> ":"
  n0 -> n10 // "" -> "Integer"
  n0 -> n11 // "" -> ";"
  n0 -> n12 // "" -> "Name"
  n0 -> n13 // "" -> ":"
  n0 -> n14 // "" -> "String"
  n0 -> n15 // "" -> ";"
  n0 -> n16 // "" -> "end"
  n0 -> n17 // "" -> ";"
  n0 -> n18 // "" -> "var"
  n0 -> n19 // "" -> "Student"
  n0 -> n20 // "" -> ":"
  n0 -> n21 // "" -> "StudentRecord"
  n0 -> n22 // "" -> ";"
  n0 -> n23 // "" -> "f"
  n0 -> n24 // "" -> ":"
  n0 -> n25 // "" -> "file"
  n0 -> n26 // "" -> "of"
  n0 -> n27 // "" -> "StudentRecord"
  n0 -> n28 // "" -> ";"
  n0 -> n29 // "" -> "begin"
  n0 -> n30 // "" -> "Assign"
  n0 -> n31 // "" -> "("
  n0 -> n32 // "" -> "f"
  n0 -> n33 // "" -> ","
  n0 -> n34 // "" -> "'MyFiledat'"
  n0 -> n35 // "" -> ")"
  n0 -> n36 // "" -> ";"
  n0 -> n37 // "" -> "Rewrite"
  n0 -> n38 // "" -> "("
  n0 -> n39 // "" -> "f"
  n0 -> n40 // "" -> ")"
  n0 -> n41 // "" -> ";"
  n0 -> n42 // "" -> "Student"
  n0 -> n43 // "" -> "."
  n0 -> n44 // "" -> "Number"
  n0 -> n45 // "" -> ":="
  n0 -> n46 // "" -> "12345"
  n0 -> n47 // "" -> ";"
  n0 -> n48 // "" -> "Student"
  n0 -> n49 // "" -> "."
  n0 -> n50 // "" -> "Name"
  n0 -> n51 // "" -> ":="
  n0 -> n52 // "" -> "'John Smith'"
  n0 -> n53 // "" -> ";"
  n0 -> n54 // "" -> "Write"
  n0 -> n55 // "" -> "("
  n0 -> n56 // "" -> "f"
  n0 -> n57 // "" -> ","
  n0 -> n58 // "" -> "Student"
  n0 -> n59 // "" -> ")"
  n0 -> n60 // "" -> ";"
  n0 -> n61 // "" -> "Close"
  n0 -> n62 // "" -> "("
  n0 -> n63 // "" -> "f"
  n0 -> n64 // "" -> ")"
  n0 -> n65 // "" -> ";"
  n0 -> n66 // "" -> "end"
  n0 -> n67 // "" -> "."

}

我的问题是：为什么所有节点都直接连接到根？如何使这个树看起来与Eclipse插件类似呢？感谢