Tutorial for walking ANTLR ASTs in C#?

Question

Is anyone aware of tutorials for walking ANTLR-generated ASTs in C#? The closest I was able to find is this, but it\'s not terribly helpful.

My goal is to walk through t

Answer 1

Normally you walk ASTs with recursion, and perform different actions based on the kind of the node. If you're using polymorphic tree nodes (i.e. different subclasses for different nodes in the tree), then double-dispatch in the Visitor pattern may be appropriate; however, that's usually not very convenient with Antlr.

In pseudocode, walking usually looks somewhat like this:

func processTree(t)
    case t.Type of
        FOO: processFoo t
        BAR: processBar t
    end

// a post-order process
func processFoo(foo)
    // visit children
    for (i = 0; i < foo.ChildCount; ++i)
        processTree(foo.GetChild(i))
    // visit node
    do_stuff(foo.getText())

// a pre-order process
func processBoo(bar)
    // visit node
    do_stuff(bar.getText())
    // visit children
    for (i = 0; i < foo.ChildCount; ++i)
        processTree(foo.GetChild(i))

The kinds of processing are highly dependent on the semantics of the language. For example, handling an IF statement, with structure (IF []), when generating code for a stack machine like the JVM or CLR, might look somewhat like this:

func processIf(n)
    predicate = n.GetChild(0)
    processExpr(predicate) // get predicate value on stack
    falseLabel = createLabel()
    genCode(JUMP_IF_FALSE, falseLabel) // JUMP_IF_FALSE is called brfalse in CLR,
                                       // ifeq in JVM
    if_true = n.GetChild(1)
    processStmt(if_true)
    if_false = n.ChildCount > 2 ? n.GetChild(2) : null
    if (if_false != null)
        doneLabel = createLabel()
        genCode(JUMP, doneLabel)
    markLabel(falseLabel)
    if (if_false != null)
        processStmt(if_false) // if-false branch
        markLabel(doneLabel)

Generally everything is done recursively depending on the type of the current node, etc.