ASTs and tree traversals
Lecture 8

(Abstract) syntax trees

Review tree traversals, differences between pre and post order, recursion

Illustrate the visitor pattern on the tree example

tree: left is either a node, leaf, or null right is either a node, leaf, or null data

walk_and_print_each_nodes_data_postorder(tree): // base if tree == null: return

// recursive step walk_and_print_each_nodes_data_postorder(tree.left) walk_and_print_each_nodes_data_postorder(tree.right) print(tree.data)

Start with the LabeledExpr grammar
Download ANTLR examples
- Start with code/tour/LabeledExpr.g4 and code/tour/Calc.java
We will hand-write the EvalVisitor.java evaluator together