AST Node Types

Abstract Syntax Trees

Tokens are a flat list. To understand structure, we build a tree. For 3 + 4 * 2, the tree shows that 4 * 2 is grouped together:

    (+)
   /   \
  3    (*)
      /   \
     4     2

Each node in the tree is called an AST node. We represent them as plain objects:

// A number literal
{ type: "NumberLiteral", value: 42 }

// A binary operation (left op right)
{ type: "BinaryExpr", op: "+", left: ..., right: ... }

Node Types We Need

Printing an AST

To verify our tree, we can write a function that converts it to a string:

function printAST(node) {
    if (node.type === "NumberLiteral") return String(node.value);
    if (node.type === "BinaryExpr") {
        return "(" + node.op + " " + printAST(node.left) + " " + printAST(node.right) + ")";
    }
}

This produces a Lisp-like format: (+ 3 (* 4 2)).

Your Task

Write helper functions num(n), str(s), and binop(op, left, right) that create AST nodes. Then write printAST(node) to display them. For StringLiteral, print the value in double quotes.