bold-engineer.js

console.log(JSON.stringify(parser.parse("(first (list 1 (+ 2 3) 9))")) == JSON.stringify(["first",["list",1,["+",2,3],9]]));

let primitives = {
  "first": (args) => {
      if (args.length != 1) {
        console.error("first called with unexpected number of arguments: ", args.length);
      }
      let the_arg = args[0];
      let the_first_of_the_arg = the_arg[0];
      return the_first_of_the_arg;
    },
  "+": (args) => args.reduce((total, element) => total + element, 0),
  "list": (args) => args
}

function my_eval(ast) {
  switch (typeof ast) {
    case "object":
      // Note: we are assuming if it is an object, then it is an array.
      let args = ast.map(my_eval);
      let f = args.shift();
      return f(args);
    case "string":
      if (primitives[ast]) {
        return primitives[ast];
      } else {
        console.error("not recognized primitive: ", ast);
        return null;
      }
    case "number":
      return ast;
    default:
      console.error("unexpected type: ", typeof ast);
  }
}

// want to see 3
console.log(my_eval(["+", 1, 2]) == 3)
// want to see 6
console.log(my_eval(["+", 1, 2, 3]) == 6)
// want to see [1, 5, 9]
console.log(JSON.stringify(my_eval(["list", 1, ["+", 2, 3], 9])) == JSON.stringify([1, 5, 9]))
// want to see 1
console.log(my_eval(["first", ["list", 1, ["+", 2, 3], 9]]) == 1)

function run(it) {
  return my_eval(parser.parse(it));
}

console.log(JSON.stringify(run("(first (list 1 (+ 2 3) 9))")) == 1);

document.querySelector("button").addEventListener("click", (e) => {
  document.querySelector("#output").innerText = run(document.querySelector("input").value);
})