AST visitor pattern?

[pcj]

Great that you are implementing the commonmark spec in java.

I like the way pegdown implements the Visitor Pattern to be able to modify or interpret the AST once constructed. Is there a similar or planned facility for commonmark-java? For example, in pegdown:

import org.pegdown.PegDownProcessor;
import org.pegdown.Extensions;
import org.pegdown.ast.RootNode;
import org.pegdown.ast.Visitor;

...

int exts
    = Extensions.DEFINITIONS
    | Extensions.AUTOLINKS
    | Extensions.HARDWRAPS
    | Extensions.TABLES
    | Extensions.STRIKETHROUGH
    | Extensions.SUPPRESS_ALL_HTML
    ;

PegDownProcessor processor = new PegDownProcessor(exts);
RootNode root = processor.parseMarkdown(s.toCharArray());

MyVisitor visitor = new MyVisitor();
root.accept(visitor);

...

class MyVisitor implements Visitor {

    @Override
    public void visit(org.pegdown.ast.Node node) {
        log.debug("visit {}", node);
    }

   ...
}

Thanks,
Paul

[robinst]

Hey!

In org.commonmark.node, there is both a Visitor interface and an AbstractVisitor class already. An example use:

Node node = parser.parse("...");
MyVisitor visitor = new MyVisitor();
node.accept(visitor);

class MyVisitor extends AbstractVisitor {
    @Override
    public void visit(Paragraph paragraph) {
        // Do something with paragraph (override other methods for other nodes):
        log.debug("visit {}", paragraph);
        // Descend into children:
        visitChildren(paragraph);
    }
}

Does that help? I guess this should be documented with an example in the README (and also do #4).

[pcj]

Yes that's it. Looks pretty obvious from the source now. Example in the README a good idea.

Thanks!

[robinst]

Done now.