tabloid-fake-closure/static/js/lang.js

/* Tabloid: the clickbait headline programming language */

/* tokenizer */

/**
 * Reads in char or word chunks
 */
class Reader {
  constructor(str, base = "") {
    this.base = base;
    this.i = 0;
    this.str = str;
  }
  peek() {
    return this.str[this.i];
  }
  next() {
    return this.str[this.i++];
  }
  hasNext() {
    return this.str[this.i] !== undefined;
  }
  backstep() {
    this.i--;
  }
  readUntil(pred) {
    let result = this.base.slice();
    while (this.hasNext() && !pred(this.peek())) {
      result += this.next();
    }
    return result;
  }
  dropWhitespace() {
    this.readUntil((c) => !!c.trim());
  }
  expect(tok) {
    const next = this.next();
    if (next !== tok) {
      throw new Error(`Parsing error: expected ${tok}, got ${next}`);
    }
  }
}

/**
 * Split into words for easier tokenization
 * with keywords.
 */
class Wordifier {
  constructor(str) {
    this.reader = new Reader(str.trim());
    this.tokens = [];
  }
  wordify() {
    if (this.tokens.length) return this.tokens;

    while (this.reader.hasNext()) {
      const next = this.reader.next();
      switch (next) {
        case "(": {
          this.tokens.push("(");
          break;
        }
        case ")": {
          this.tokens.push(")");
          break;
        }
        case ",": {
          this.tokens.push(",");
          break;
        }
        case '"':
        case "'": {
          this.wordifyString(next);
          break;
        }
        default: {
          // read until WS
          this.reader.backstep();
          this.tokens.push(
            this.reader.readUntil((c) => {
              return !c.trim() || ["(", ")", ","].includes(c);
            })
          );
        }
      }
      this.reader.dropWhitespace();
    }
    return this.tokens;
  }
  wordifyString(endChar) {
    let acc = "";
    acc += this.reader.readUntil((c) => c == endChar);
    while (acc.endsWith("\\") || !this.reader.hasNext()) {
      acc = acc.substr(0, acc.length - 1);
      this.reader.next(); // endChar
      acc += endChar + this.reader.readUntil((c) => c == endChar);
    }
    this.reader.next(); // throw away closing char
    this.tokens.push('"' + acc);
  }
}

const T = {
  LParen: Symbol("LParen"),
  RParen: Symbol("RParen"),
  Comma: Symbol("Comma"),
  DiscoverHowTo: Symbol("DiscoverHowTo"),
  With: Symbol("With"),
  Of: Symbol("Of"),
  RumorHasIt: Symbol("RumorHasIt"),
  WhatIf: Symbol("WhatIf"),
  LiesBang: Symbol("LiesBang"),
  EndOfStory: Symbol("EndOfStory"),
  ExpertsClaim: Symbol("ExpertsClaim"),
  ToBe: Symbol("ToBe"),
  YouWontWantToMiss: Symbol("YouWontWantToMiss"),
  LatestNewsOn: Symbol("LatestNewsOn"),
  TotallyRight: Symbol("TotallyRight"),
  CompletelyWrong: Symbol("CompletelyWrong"),
  IsActually: Symbol("IsActually"),
  And: Symbol("And"),
  Or: Symbol("Or"),
  Plus: Symbol("Plus"),
  Minus: Symbol("Minus"),
  Times: Symbol("Times"),
  DividedBy: Symbol("DividedBy"),
  Modulo: Symbol("Modulo"),
  Beats: Symbol("Beats"), // >
  SmallerThan: Symbol("SmallerThan"), // <
  ShockingDevelopment: Symbol("ShockingDevelopment"),
  PleaseLikeAndSubscribe: Symbol("PleaseLikeAndSubscribe"),
};

const BINARY_OPS = [
  T.IsActually,
  T.And,
  T.Or,
  T.Plus,
  T.Minus,
  T.Times,
  T.DividedBy,
  T.Modulo,
  T.Beats,
  T.SmallerThan,
];

function tokenize(prog) {
  const reader = new Reader(new Wordifier(prog).wordify(), []);
  const tokens = [];

  while (reader.hasNext()) {
    const next = reader.next();
    switch (next) {
      case "DISCOVER": {
        reader.expect("HOW");
        reader.expect("TO");
        tokens.push(T.DiscoverHowTo);
        break;
      }
      case "WITH": {
        tokens.push(T.With);
        break;
      }
      case "OF": {
        tokens.push(T.Of);
        break;
      }
      case "RUMOR": {
        reader.expect("HAS");
        reader.expect("IT");
        tokens.push(T.RumorHasIt);
        break;
      }
      case "WHAT": {
        reader.expect("IF");
        tokens.push(T.WhatIf);
        break;
      }
      case "LIES!": {
        tokens.push(T.LiesBang);
        break;
      }
      case "END": {
        reader.expect("OF");
        reader.expect("STORY");
        tokens.push(T.EndOfStory);
        break;
      }
      case "EXPERTS": {
        reader.expect("CLAIM");
        tokens.push(T.ExpertsClaim);
        break;
      }
      case "TO": {
        reader.expect("BE");
        tokens.push(T.ToBe);
        break;
      }
      case "YOU": {
        reader.expect("WON'T");
        reader.expect("WANT");
        reader.expect("TO");
        reader.expect("MISS");
        tokens.push(T.YouWontWantToMiss);
        break;
      }
      case "LATEST": {
        reader.expect("NEWS");
        reader.expect("ON");
        tokens.push(T.LatestNewsOn);
        break;
      }
      case "IS": {
        reader.expect("ACTUALLY");
        tokens.push(T.IsActually);
        break;
      }
      case "AND": {
        tokens.push(T.And);
        break;
      }
      case "OR": {
        tokens.push(T.Or);
        break;
      }
      case "PLUS": {
        tokens.push(T.Plus);
        break;
      }
      case "MINUS": {
        tokens.push(T.Minus);
        break;
      }
      case "TIMES": {
        tokens.push(T.Times);
        break;
      }
      case "DIVIDED": {
        reader.expect("BY");
        tokens.push(T.DividedBy);
        break;
      }
      case "MODULO": {
        tokens.push(T.Modulo);
        break;
      }
      case "BEATS": {
        tokens.push(T.Beats);
        break;
      }
      case "SMALLER": {
        reader.expect("THAN");
        tokens.push(T.SmallerThan);
        break;
      }
      case "SHOCKING": {
        reader.expect("DEVELOPMENT");
        tokens.push(T.ShockingDevelopment);
        break;
      }
      case "PLEASE": {
        reader.expect("LIKE");
        reader.expect("AND");
        reader.expect("SUBSCRIBE");
        tokens.push(T.PleaseLikeAndSubscribe);
        break;
      }
      case "TOTALLY": {
        reader.expect("RIGHT");
        tokens.push(T.TotallyRight);
        break;
      }
      case "COMPLETELY": {
        reader.expect("WRONG");
        tokens.push(T.CompletelyWrong);
        break;
      }
      case "(": {
        tokens.push(T.LParen);
        break;
      }
      case ")": {
        tokens.push(T.RParen);
        break;
      }
      case ",": {
        tokens.push(T.Comma);
        break;
      }
      default: {
        if (!isNaN(parseFloat(next))) {
          // number literal
          tokens.push(parseFloat(next));
        } else {
          // string or varname
          tokens.push(next);
        }
      }
    }
  }
  return tokens;
}

/* parser */

const N = {
  NumberLiteral: Symbol("NumberLiteral"),
  StringLiteral: Symbol("StringLiteral"),
  BoolLiteral: Symbol("BoolLiteral"),
  FnDecl: Symbol("FnDecl"),
  FnCall: Symbol("FnCall"),
  Ident: Symbol("Ident"),
  Assignment: Symbol("Assignment"),
  BinaryOp: Symbol("BinaryOp"),
  IfExpr: Symbol("IfExpr"),
  ExprGroup: Symbol("ExprGroup"),
  ReturnExpr: Symbol("ReturnExpr"),
  ProgEndExpr: Symbol("ProgEndExpr"),
  PrintExpr: Symbol("PrintExpr"),
  InputExpr: Symbol("InputExpr"),
};

class Parser {
  constructor(tokens) {
    this.tokens = new Reader(tokens, []);
  }
  /**
   * Atom
   *  Ident
   *  NumberLiteral
   *  StringLiteral
   *  BoolLiteral
   *  FnCall
   *  FnDecl
   *  ExprGroup
   *
   * Expression:
   *  (begins with atom)
   *      BinaryOp
   *      Atom
   *  (begins with keyword)
   *      IfExpr
   *      Assignment
   *      ReturnExpr
   *      ProgEndExpr
   *      PrintExpr
   *      InputExpr
   *
   */
  parse() {
    const nodes = [];
    while (this.tokens.hasNext()) {
      nodes.push(this.expr());
    }

    if (nodes[nodes.length - 1].type !== N.ProgEndExpr) {
      throw new Error(
        "Parsing error: A Tabloid program MUST end with PLEASE LIKE AND SUBSCRIBE"
      );
    }

    return nodes;
  }
  expectIdentString() {
    const ident = this.tokens.next();
    if (typeof ident === "string" && !ident.startsWith('"')) {
      return ident;
    }
    throw new Error(
      `Parsing error: expected identifier, got ${ident.toString()}`
    );
  }
  atom() {
    const next = this.tokens.next();
    if (typeof next === "number") {
      return {
        type: N.NumberLiteral,
        val: next,
      };
    } else if (typeof next === "string") {
      if (next.startsWith('"')) {
        return {
          type: N.StringLiteral,
          val: next.substr(1),
        };
      }
      const ident = {
        type: N.Ident,
        val: next,
      };
      if (this.tokens.peek() === T.Of) {
        return this.fnCall(ident);
      }
      return ident;
    } else if (next === T.TotallyRight) {
      return {
        type: N.BoolLiteral,
        val: true,
      };
    } else if (next === T.CompletelyWrong) {
      return {
        type: N.BoolLiteral,
        val: false,
      };
    } else if (next === T.DiscoverHowTo) {
      // fn literal
      const fnName = this.tokens.next();
      if (this.tokens.peek(T.With)) {
        this.tokens.next(); // with
        // with args
        const args = [this.expectIdentString()];
        while (this.tokens.peek() === T.Comma) {
          this.tokens.next(); // comma
          args.push(this.expectIdentString());
        }
        return {
          type: N.FnDecl,
          name: fnName,
          args: args,
          body: this.expr(),
        };
      } else {
        return {
          type: N.FnDecl,
          name: fnName,
          args: [],
          body: this.expr(),
        };
      }
    } else if (next === T.RumorHasIt) {
      // block
      const exprs = [];
      while (this.tokens.hasNext() && this.tokens.peek() !== T.EndOfStory) {
        exprs.push(this.expr());
      }
      this.tokens.expect(T.EndOfStory);
      return {
        type: N.ExprGroup,
        exprs: exprs,
      };
    } else if (next === T.LParen) {
      // block, but guarded by parens, for binary exprs
      const exprs = [];
      while (this.tokens.hasNext() && this.tokens.peek() !== T.RParen) {
        exprs.push(this.expr());
      }
      this.tokens.expect(T.RParen);
      return {
        type: N.ExprGroup,
        exprs: exprs,
      };
    }

    throw new Error(
      `Parsing error: expected ident, literal, or block, got ${next.toString()} before ${this.tokens
        .peek()
        .toString()}`
    );
  }
  expr() {
    const next = this.tokens.next();
    if (next === T.WhatIf) {
      // if expr
      const cond = this.expr();
      const ifBody = this.expr();

      let elseBody = null;
      if (this.tokens.peek() == T.LiesBang) {
        this.tokens.next(); // LiesBang
        elseBody = this.expr();
      }
      return {
        type: N.IfExpr,
        cond: cond,
        ifBody: ifBody,
        elseBody: elseBody,
      };
    } else if (next === T.ExpertsClaim) {
      // assignment
      const name = this.expectIdentString();
      this.tokens.expect(T.ToBe);
      const val = this.expr();
      return {
        type: N.Assignment,
        name,
        val,
      };
    } else if (next === T.ShockingDevelopment) {
      // return
      return {
        type: N.ReturnExpr,
        val: this.expr(),
      };
    } else if (next === T.PleaseLikeAndSubscribe) {
      // prog end
      return {
        type: N.ProgEndExpr,
      };
    } else if (next === T.YouWontWantToMiss) {
      // print expr
      return {
        type: N.PrintExpr,
        val: this.expr(),
      };
    } else if (next === T.LatestNewsOn) {
      // input expr
      return {
        type: N.InputExpr,
        val: this.expr(),
      };
    }

    this.tokens.backstep();
    const atom = this.atom();
    if (BINARY_OPS.includes(this.tokens.peek())) {
      // infix binary ops
      const left = atom;
      const op = this.tokens.next();
      const right = this.atom();
      return {
        type: N.BinaryOp,
        op,
        left,
        right,
      };
    }

    return atom;
  }
  fnCall(fnNode) {
    this.tokens.expect(T.Of);
    const args = [this.expr()];
    while (this.tokens.peek() === T.Comma) {
      this.tokens.next(); // comma
      args.push(this.expr());
    }
    //    if (this.tokens.peek() === T.Of) {
    //      const x = this.fnCall(fnNode);
    //      return {
    //        type: N.FnCall,
    //        fn: x,
    //        args: args,
    //      };
    //    }

    const x = {
      type: N.FnCall,
      fn: fnNode,
      args: args,
    };
    //    console.log("Top", x);
    return x;
  }
}

/* executor (tree walk) */

/**
 * Abused (slightly) to easily return values upstack
 */
class ReturnError {
  constructor(value) {
    this.value = value;
  }
  unwrap() {
    return this.value;
  }
}

class Environment {
  constructor(runtime) {
    /**
     * Runtime contains the following functions:
     *  - print(s)
     *  - input(s)
     */
    this.runtime = runtime;
    this.scopes = [{}]; // begin with global scope
  }
  run(nodes) {
    let rv;
    for (const node of nodes) {
      rv = this.eval(node);
    }
    return rv;
  }

  putClosureOnAllSubNodes(node, closure) {
    if (Array.isArray(node)) {
      for (let i = 0; i < node.length; ++i) {
        node[i] = this.putClosureOnAllSubNodes(node[i], closure);
      }
    } else if (typeof node === "object") {
      for (let key of Object.keys(node)) {
        node[key] = this.putClosureOnAllSubNodes(node[key], closure);
      }
      node.closure = { ...closure };
    }
    return node;
  }

  eval(node) {
    const scope = this.scopes[this.scopes.length - 1];

    switch (node.type) {
      case N.NumberLiteral:
      case N.StringLiteral:
      case N.BoolLiteral:
        return node.val;
      case N.FnDecl: {
        console.log("DECL", node, scope);
        node.closure = { ...scope };
        if (node.closure) {
          node.closure = { ...node.closure, ...scope };
        }
        scope[node.name] = node;
        return node;
      }
      case N.FnCall: {
        const fn = this.eval(node.fn);

        console.log("fn - closure", node);
        fn.body = this.putClosureOnAllSubNodes(fn.body, fn.closure);
        console.log("fn", fn);

        const args = node.args.map((arg) => this.eval(arg));
        const calleeScope = {};
        fn.args.forEach((argName, i) => {
          calleeScope[argName] = args[i];
        });

        this.scopes.push(calleeScope);
        let rv;
        try {
          this.eval(fn.body);
        } catch (maybeReturnErr) {
          if (maybeReturnErr instanceof ReturnError) {
            rv = maybeReturnErr.unwrap();
          } else {
            // re-throw
            throw maybeReturnErr;
          }
        }
        this.scopes.pop();

        return rv;
      }
      case N.Ident: {
        let i = this.scopes.length - 1;
        while (i >= 0) {
          if (node.val in this.scopes[i]) {
            return this.scopes[i][node.val];
          }
          i--;
        }
        if (node.closure && node.closure.hasOwnProperty(node.val)) {
          return node.closure[node.val];
        }
        throw new Error(`Runtime error: Undefined variable "${node.val}"`);
      }
      case N.Assignment: {
        scope[node.name] = this.eval(node.val);
        console.log("assn", node);
        return scope[node.name];
      }
      case N.BinaryOp: {
        const left = this.eval(node.left);
        const right = this.eval(node.right);
        switch (node.op) {
          case T.IsActually:
            return left === right;
          case T.And:
            return left && right;
          case T.Or:
            return left || right;
          case T.Plus:
            return left + right;
          case T.Minus:
            return left - right;
          case T.Times:
            return left * right;
          case T.DividedBy:
            return left / right;
          case T.Modulo:
            return left % right;
          case T.Beats:
            return left > right;
          case T.SmallerThan:
            return left < right;
          default:
            throw new Error(
              `Runtime error: Unknown binary op ${node.op.toString()}`
            );
        }
      }
      case N.IfExpr: {
        if (this.eval(node.cond)) {
          return this.eval(node.ifBody);
        }
        if (node.elseBody != null) {
          return this.eval(node.elseBody);
        }
      }
      case N.ExprGroup: {
        if (!node.exprs.length) {
          throw new Error(
            "Runtime error: Empty expression group with no expressions"
          );
        }

        let rv;
        for (const expr of node.exprs) {
          rv = this.eval(expr);
        }
        return rv;
      }
      case N.ReturnExpr: {
        const rv = this.eval(node.val);
        throw new ReturnError(rv);
      }
      case N.ProgEndExpr: {
        // do nothing
        break;
      }
      case N.PrintExpr: {
        let val = this.eval(node.val);
        // shim for boolean to-string's
        if (val === true) {
          val = "TOTALLY RIGHT";
        } else if (val === false) {
          val = "COMPLETELY WRONG";
        }
        this.runtime.print(val);
        return val;
      }
      case N.InputExpr: {
        let val = this.eval(node.val);
        // shim for boolean to-string's
        if (val === true) {
          val = "TOTALLY RIGHT";
        } else if (val === false) {
          val = "COMPLETELY WRONG";
        }
        return this.runtime.input(val);
      }
      default:
        console.log(JSON.stringify(node, null, 2));
        throw new Error(
          `Runtime error: Unknown AST Node of type ${node.type.toString()}:\n${JSON.stringify(
            node,
            null,
            2
          )}`
        );
    }
  }
}