Pico8 (Lua subset) hand rolled parser/lexer

plexy.js

function plexy(src) {
  const TOKEN = {
    STRING: 0,
    NUMBER: 1,
    LABEL: 2,
    SYMBOL: 3,
    '...': 4,
    '..': 5,
    '.': 6,
    '==': 7,
    '=': 8,
    '~=': 9,
    '<=': 10,
    '<': 11,
    '>=': 12,
    '>': 13,
    '-=': 14,
    '-': 15,
    '+=': 16,
    '+': 17,
    '/=': 18,
    '/': 19,
    '*': 20,
    '*=': 21,
    '%=': 22,
    '%': 23,
    '^=': 24,
    '^': 25,
    '#': 26,
    ':': 27,
    ';': 28,
    ',': 29,
    '(': 30,
    ')': 31,
    '{': 32,
    '}': 33,
    '[': 34,
    ']': 35,
    'and': 36,
    'continue': 37,
    'do': 38,
    'else': 39,
    'elseif': 40,
    'end': 41,
    'false': 42,
    'for': 43,
    'function': 44,
    'goto': 45,
    'if': 46,
    'in': 47,
    'local': 48,
    'nil': 49,
    'not': 50,
    'or': 51,
    'repeat': 52,
    'return': 53,
    'then': 54,
    'true': 55,
    'until': 56,
    'while': 57
  };

  var tokens = [];
  function addToken(token, start, end = start + 1) {
    return tokens.push({token: token, start: start, end: end});
  }
  function isDigit(c) { return c >= '0' && c <= '9'; }
  function isAlpha(c) { return (c >= 'a' && c <= 'z') || c === '_'; }

  for (var i = 0; i < src.length; i++) {
    var c = src[i];
    // whitespace (ignore)
    if (c === ' ' || c === '\t' || c === '\r' || c === '\n') {
      while (++i < src.length && (src[i] === ' '  || src[i] === '\t' ||
                                  src[i] === '\r' || src[i] === '\n'));
      c = src[i];
    }

    // comment
    if (c === '-' && src[i+1] === '-') {
      if (src[i+2] === '[' && src[i+3] === '[') {
        i = src.indexOf(']]--', i + 4) + 3;
      } else {
        i = src.indexOf('\n', i + 2);
      }
      continue;
    }

    if (isDigit(c)) {
      var s = i;
      while (++i < src.length && isDigit(src[i]));
      addToken(TOKEN.NUMBER, s, i);
      --i;
      continue;
    }

    if (isAlpha(c)) {
      var s = i;
      while (++i < src.length && (isAlpha(src[i]) || isDigit(src[i])));
      addToken(TOKEN[src.substring(s, i)] || TOKEN.SYMBOL, s, i);
      --i;
      continue;
    }

    switch (c) {
      case '"': case "'":
        var s = i + 1;
        do { i = src.indexOf(c, i + 1); } while (i < src.length && src[i-1] === '\\');
        addToken(TOKEN.STRING, s, i - 1);
        break;
      case '.':
        src[i+1] === '.'
          ? src[i+2] === '.'
            ? addToken(TOKEN['...'], i, i += 2)
            : addToken(TOKEN['..'], i, ++i)
          : addToken(TOKEN['.'], i);
        break;
      case ':':
        if (src[i+1] === ':') {
          s = i + 2;
          i = src.indexOf('::', s) + 1;
          addToken(TOKEN.LABEL, s, i - 2);
          break;
        }
      case '=': case '-': case '+': case '*': case '/':
      case '<': case '>': case '%': case '^':
        if (src[i+1] === '=') {
          addToken(TOKEN[c+'='], i, ++i);
          break;
        }
      case '#': case ';': case ',': case '(': case ')':
      case '{': case '}': case '[': case ']':
        addToken(TOKEN[c], i);
        break;
      case '~': // let it just flow though we ignore ~ by itself.
        if (src[i+1] === '=') {
          addToken(TOKEN['~='], i, ++i);
        }
      default:
        console.log('>>', c, i, '<<');
    }
  }
  return tokens;
}

/*
var src = `
-- hello world
-- by zep

t = 0

function _update()
 t += 1
end

function _draw()
 cls()
  
 for i=1,11 do
  for j0=0,7 do
  j = 7-j0
  col = 7+j
  t1 = t + i*4 - j*2
  x = cos(t0)*5
  y = 38 + j + cos(t1/50)*5
  pal(7,col)
  spr(16+i, 8+i*8 + x, y)
  end
 end
 
  print("this is pico-8",
    37, 70, 14) --8+(t/4)%8)

 print("nice to meet you",
    34, 80, 12) --8+(t/4)%8)
end`;
plexy(src).map((t) => src.substring(t.start, t.end));*/