[antlr-interest] v3: going through the AST

[Thomas Brandon]

Without any restructuring the default tree output from a grammar will
be a single tree node for each token, without any child or parent
relationships. So a rule "a: A B C;" will simply produce the tree "A B
C" which is basically a linked list. You need to add either tree
rewrite rules or tree operators to structure the tree as you would
like. For instance to make a give token the root suffix it with "^".
So something like "a: A^ B C;"
would produce the tree "(A B C)". Or you can use a rewrite rule. So
"a: A B C -> ^(A C B);" would produce the tree "(A C B)".

Also, the Antlrworks debug functionality will allow you to view the
AST tree in a visual form rather than having to print it out to text.

Tom.
On 8/16/06, Dieter Frej <dieter_frej at gmx.net> wrote:
> Hi,
>
> I added output=AST; to the options section of the latest java.g grammar in
> order to get the AST. This makes a new method public Object getTree()
> available.
> What I would like to get was something like the tree structure visualised
> in antlrworks. So I tried the following:
>
> CommonTree tree = (CommonTree) parser.compilationUnit().getTree();
> String[] names = parser.getTokenNames();
> int childCount = tree.getChildCount();
> for(int i = 0; i < childCount; ++i) {
>     CommonTree ct = (CommonTree) tree.getChild(i);
>     System.out.println("childcount: " + ct.getChildCount());
>     System.out.println("tree type: " + ct.getType() + "|" + names[ct.getType()]);
>     System.out.println("text: " + ct.token.getText());
>     System.out.println("line: " + ct.getLine());
>     System.out.println("toString: " + ct.toString());
>     System.out.println("toStringTree: " + ct.toStringTree());
>     System.out.println();
> }
>
> but tree.getChildCount() is always 1. It is more like a linked list than a
> tree.
>
> Any suggestions? Or is my code wrong? (because of the lack of examples
> that could also be the case ;-)
>
> - Didi
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>
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