[antlr-interest] Re: AST writer

[thrutchy]

--- In antlr-interest at yahoogroups.com, "atripp54321" <atripp at c...> wrote:
> --- In antlr-interest at yahoogroups.com, "thrutchy" <eric_mahurin at y...>
> wrote:
> > Is there a way to write out an AST in the same format as it was
> parsed
> > into the AST without having to write a tree-parser rule for each
> rule
> > of the parser?  To do this, I would assume you couldn't put in any
> > "!"/"^" in the rules and the text can't be munged or ignored (i.e.
> > whitespace/comments).
> > 
> > I would like to write a language munger that does this:
> > 
> > 1. Read language input into an AST
> > 
> > 2. Do manipulations to the AST (via a tree-walker or manually)
> > 
> > 3. Write the AST out in the same input language
> > 
> > I would prefer not to have to specify the language twice - once in
> the
> > parser and once in the writer.
> 
> It seems to me that if you avoid "!" and all the other fancy
> ANTLR constructs in your grammar (other than "^", which you do
> need, as Monty points out), then your language output really
> could be just an in-order traversal of the AST.
> 
> One thing you might want to try is to compare the java.g that
> compes with ANTLR with the print() method in
> this code that prints out a Java AST:
> http://jazillian.com/antlr/JavaEmitter.java
> The java.g strips out all the "syntax stuff", and this code
> puts it all back in.
> 
> Andy


Thanks guys.  I've finally had some time to figure out the AST's. 
Below is what I came up with if you don't do any of this:

- use "!" or manipulate the text (i.e. remove quotes from strings)
- root anything but the first thing in a rule (you could use imaginary
tokens where needed)

I'm also using the stuff from preserve whitespace example.  Here what
I have:

public static void printHiddenBefore(AST a) {
    java.util.List before = new ArrayList();
    for (
        CommonHiddenStreamToken t =
((CommonASTWithHiddenTokens)a).getHiddenBefore() ;
        t!=null ;
        t = t.getHiddenBefore() )
    {
        before.add(t.getText());
    }
    for (int i=before.size()-1;i>=0;--i) {
        System.out.print(before.get(i));
    }
}
public static void printAST(AST a) {
    while (a!=null) {
        String s = a.toString();
        if (s!=null) System.out.print(s);
        for (
            CommonHiddenStreamToken t =
((CommonASTWithHiddenTokens)a).getHiddenAfter() ;
            t!=null ;
            t = t.getHiddenAfter() )
        {
            System.out.print(t.getText());
        }
        printAST(a.getFirstChild());
        a = a.getNextSibling();
    }
}


Just call these two in sequence using the root AST node.

Eric




 
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