toAST.js

const ASTNode = require("./astNode");
const nodeTypes = require("./nodeTypes");
const tokenTypes = require("./tokenTypes");

function additive(tokenReader) {
  let child1 = multiply(tokenReader);
  let node = child1;
  if (child1 != null) {
    while (true) {
      let token = tokenReader.peek();
      if (
        token != null &&
        (token.type === tokenTypes.Plus || token.type === tokenTypes.Minus)
      ) {
        token = tokenReader.read();
        let child2 = multiply(tokenReader);
        node = new ASTNode(
          token.type === tokenTypes.Plus ? nodeTypes.Additive : nodeTypes.Minus
        );
        node.appendChild(child1);
        node.appendChild(child2);
        child1 = node;
      } else {
        break;
      }
    }
  }
  return node;
}
function multiply(tokenReader) {
  let child1 = primary(tokenReader);
  let node = child1;
  if (child1 != null) {
    while (true) {
      let token = tokenReader.peek();
      if (
        token != null &&
        (token.type === tokenTypes.Multiply || token.type === tokenTypes.Divide)
      ) {
        token = tokenReader.read();
        let child2 = primary(tokenReader);
        node = new ASTNode(
          token.type === tokenTypes.Multiply
            ? nodeTypes.Multiplicative
            : nodeTypes.Divide
        );
        node.appendChild(child1);
        node.appendChild(child2);
        child1 = node;
      } else {
        break;
      }
    }
  }
  return node;
}
function primary(tokenReader) {
  let node = number(tokenReader);
  if (!node) {
    let token = tokenReader.peek();
    if (token != null && token.type === tokenTypes.LeftPara) {
      tokenReader.read();
      node = additive(tokenReader);
      tokenReader.read();
    }
  }
  return node;
}
function number(tokenReader) {
  let node = null;
  let token = tokenReader.peek();
  if (token != null && token.type === tokenTypes.Number) {
    token = tokenReader.read();
    node = new ASTNode(nodeTypes.Numeric, token.value);
  }
  return node;
}

function toAST(tokenReader) {
  let rootNode = new ASTNode(nodeTypes.Program);
  let child = additive(tokenReader);
  if (child) {
    rootNode.appendChild(child);
  }
  return rootNode;
}

module.exports = toAST;