openai.js

function parseSExp(input) {
  const tokens = tokenize(input);
  const [exp, remainingTokens] = readFromTokens(tokens);
  
  if (remainingTokens.length !== 0) {
    throw new SyntaxError(`unexpected token(s): ${remainingTokens.join(' ')}`);
  }
  
  return exp;
}

function tokenize(input) {
  return input
    .replace(/\(/g, ' ( ')
    .replace(/\)/g, ' ) ')
    .trim()
    .split(/\s+/);
}

function readFromTokens(tokens) {
  if (tokens.length === 0) {
    throw new SyntaxError('unexpected EOF while reading');
  }

  const token = tokens.shift();

  if (token === '(') {
    return readList(tokens);
  } else if (token === ')') {
    throw new SyntaxError('unexpected )');
  } else {
    return readAtom(token);
  }
}

function readList(tokens) {
  const lst = [];

  while (tokens[0] !== ')') {
    const [exp, remainingTokens] = readFromTokens(tokens);
    lst.push(exp);
    tokens = remainingTokens;
  }

  if (tokens.shift() !== ')') {
    throw new SyntaxError('missing closing )');
  }

  return [lst, tokens];
}

function readAtom(token) {
  const num = parseFloat(token);

  if (!isNaN(num)) {
    return [num, []];
  } else if (token.startsWith('"')) {
    return readString(token);
  } else if (token === '#t') {
    return [true, []];
  } else if (token === '#f') {
    return [false, []];
  } else if (token === '#\\newline') {
    return ['\n', []];
  } else if (token.startsWith('#\\')) {
    return [readChar(token), []];
  } else {
    return [token, []];
  }
}

function readString(token) {
  let str = '';
  let i = 0;

  while (i < token.length) {
    if (token[i] === '\\') {
      if (token[i+1] === 'n') {
        str += '\n';
        i += 2;
      } else if (token[i+1] === '"') {
        str += '"';
        i += 2;
      } else if (token[i+1] === '\\') {
        str += '\\';
        i += 2;
      } else {
        throw new SyntaxError(`invalid escape sequence: \\${token[i+1]}`);
      }
    } else if (token[i] === '"') {
      return [str, []];
    } else {
      str += token[i];
      i++;
    }
  }

  throw new SyntaxError('missing closing "');
}

function readChar(token) {
  if (token === '#\\space') {
    return ' ';
  } else if (token === '#\\tab') {
    return '\t';
  } else if (token === '#\\return') {
    return '\r';
  } else if (token.length === 3) {
    return token[2];
  } else {
    throw new SyntaxError(`invalid character literal: ${token}`);
  }
}