metagen/parser2.inc.php

<?php

class mtgMetaInfoParser2 implements mtgIMetaInfoParser
{
  const T_NonOrdMark         = 1000; //marks start of non 'ord(..)' values
  const T_EOF                = 1001;
  const T_StringConstant     = 1002;
  const T_IntegerConstant    = 1003;
  const T_FloatConstant      = 1004;
  const T_Enum               = 1005;
  const T_RPC                = 1006;
  const T_UserSymbol         = 1008;
  const T_Struct             = 1009;
  const T_Prop               = 1010;
  const T_Extends            = 1011;
  const T_Func               = 1012;
  const T_RawStringConstant  = 1013;
  const T_Interface          = 1014;
  const T_Implements         = 1015;
  const T_MinType            = 1019; //built-in types begin mark
  const T_string             = 1020;
  const T_uint32             = 1021;
  const T_int32              = 1022;
  const T_uint16             = 1023;
  const T_int16              = 1024;
  const T_uint8              = 1025;
  const T_int8               = 1026;
  const T_float              = 1027;
  const T_uint64             = 1028;
  const T_int64              = 1029;
  const T_bool               = 1030;
  const T_blob               = 1031;
  const T_Service            = 1032;
  const T_MaxType            = 1034; //built-in types end mark

  private array $config = array();
  private mtgMetaInfo $current_meta;
  private array $parsed_files = array();
  private array $file_stack = array();
  private ?mtgMetaParsedModule $module = null;
  private string $file = "";
  private string $source = "";
  private int $cursor_pos = 0;
  private string $cursor_char = '';
  private int $line = 0;
  //TODO: setting it an 'int' type makes PHPStan produce many 
  //      false positives
  //token numeric identifier 
  private $T = 0;
  //token extra string value which depends on concrete T 
  private string $T_value = "";
  /** @var array<string,int>*/
  private $symbol2T = array();
  /** @var array<int,string>*/
  private $T2descr = array();
  private array $shared_tokens = array();
  private array $scopes = array();

  function __construct($config = array())
  {
    $this->_initTables();

    self::_addDefaultTokens($config);

    $this->config = $config;
    if(!isset($this->config['include_path']))
      $this->config['include_path'] = array('.');
  }

  private function _initTables()
  {
    $this->symbol2T = [
      "string" => self::T_string,
      "uint32" => self::T_uint32,
      "int32" => self::T_int32,
      "uint16" => self::T_uint16,
      "int16" => self::T_int16,
      "uint8" => self::T_uint8,
      "int8" => self::T_int8,
      "float" => self::T_float,
      "double" => self::T_float,
      "uint64" => self::T_uint64,
      "int64" => self::T_int64,
      "bool" => self::T_bool,
      "blob" => self::T_blob,

      "true" => self::T_IntegerConstant,
      "false" => self::T_IntegerConstant,

      "struct" => self::T_Struct,
      "interface" => self::T_Interface,
      "enum" => self::T_Enum,
      "RPC" => self::T_RPC,
      "service" => self::T_Service,
      "extends" => self::T_Extends,
      "implements" => self::T_Implements,
      "func" => self::T_Func,
    ];

    $this->T2descr = array_flip($this->symbol2T);
    $this->T2descr[self::T_EOF] = '<EOF>';
    $this->T2descr[self::T_StringConstant] = '<StringConstant>';
    $this->T2descr[self::T_RawStringConstant] = '<RawStringConstant>';
    $this->T2descr[self::T_IntegerConstant] = '<IntegerConstant>';
    $this->T2descr[self::T_FloatConstant] = '<FloatConstant>';
    $this->T2descr[self::T_Enum] = '<enum>';
    $this->T2descr[self::T_RPC] = '<RPC>';
    $this->T2descr[self::T_Service] = '<Service>';
    $this->T2descr[self::T_UserSymbol] = '<Identifier>';
    $this->T2descr[self::T_Struct] = '<struct>';
    $this->T2descr[self::T_Interface] = '<interface>';
    $this->T2descr[self::T_Prop] = '<@prop>';
    $this->T2descr[self::T_Extends] = '<extends>';
    $this->T2descr[self::T_Implements] = '<implements>';
    $this->T2descr[self::T_Func] = '<func>';
  }

  private static function _addDefaultTokens(array &$config)
  {
    if(!isset($config['valid_tokens']))
      $config['valid_tokens'] = array();

    $config['valid_tokens'][] = 'class_id';
    $config['valid_tokens'][] = 'shared_tokens';
    $config['valid_tokens'][] = 'enum_override';
    $config['valid_tokens'][] = 'enum_replace';
  }

  function parse(mtgMetaInfo $meta, string $raw_file)
  {
    $this->current_meta = $meta;

    $file = realpath($raw_file);
    if($file === false)
      throw new Exception("No such file '$raw_file'");

    $this->_parse($file);
  }

  private function _parse(string $file)
  {
    if(isset($this->parsed_files[$file]))
      return;
    $module = new mtgMetaParsedModule($file);
    $this->parsed_files[$file] = $module;
    $this->file_stack[] = $file;
    $source = file_get_contents($file);

    try
    {
      if($source === false)
        throw new Exception("Could not read file '$file'");

      $this->_resolveIncludes($module, $source);
    }
    catch(Exception $e)
    {
      throw new Exception(end($this->file_stack) . " : " . $e->getMessage());
    }

    array_pop($this->file_stack);

    $this->module = $module;
    $this->file = $file;
    $this->source = $source;
    $this->line = 1;
    $this->cursor_pos = -1;
    $this->_cursorNext();
    $this->shared_tokens = array();

    try
    {
      $this->_nextT();
      while($this->T != self::T_EOF)
      {
        if($this->T == self::T_Prop)
          $this->_parseSharedTokens($this->_parsePropTokens());
        else if($this->T == self::T_Enum)
          $this->_parseEnum();
        else if($this->T == self::T_Struct)
          $this->_parseStruct();
        else if($this->T == self::T_Interface)
          $this->_parseInterface();
        else if($this->T == self::T_Func)
          $this->_parseFreeFunc();
        else if($this->T == self::T_RPC)
          $this->_parseRPC();
        else if($this->T == self::T_Service)
          $this->_parseService();
        else
          $this->_error("Unexpected symbol ('" . $this->_toStr($this->T) . "' " . $this->T_value . ")");
      }
    }
    catch(Exception $e)
    {
      throw new Exception("$file@{$this->line} : " .  $e->getMessage() . " " . $e->getTraceAsString());
    }
  }

  private function _parseInclude(mtgMetaParsedModule $module, string $file)
  {
    $this->_parse($file);

    $module->addInclude($this->parsed_files[$file]);
  }

  private function _parseSharedTokens(array $tokens)
  {
    if(!isset($tokens['shared_tokens']))
      return;

    $this->shared_tokens = json_decode($tokens['shared_tokens'], true);
    if(!is_array($this->shared_tokens))
      $this->_error("Invalid 'shared_tokens' formant, invalid JSON");
  }

  private function _parseType(bool $can_be_multi = false)
  {
    $types = array();

    while(true)
    {
      $type = null;
      
      if($this->T == self::T_Func)
      {
        $origin = new mtgOrigin($this->file, $this->line);
        $func_type = $this->_parseFuncType();
        $type = new mtgTypeRef($func_type, $this->_scope(), $origin);
      }
      else if($this->T == self::T_UserSymbol)
      {
        $origin = new mtgOrigin($this->file, $this->line);
        $type_name = $this->_parseDotName();
        $type = new mtgTypeRef($type_name, $this->_scope(), $origin);
      }
      else
      {
        $origin = new mtgOrigin($this->file, $this->line);
        $type_name = $this->T_value;
        $type = new mtgTypeRef(new mtgBuiltinType($type_name), $this->_scope(), $origin);
        $this->_nextT();
      }

      if($this->T == ord('['))
      {
        $origin = new mtgOrigin($this->file, $this->line);
        $this->_nextT();
        $this->_checkThenNext(ord(']'));
        $type = new mtgTypeRef(new mtgArrType($type), $this->_scope(), $origin);
      }
      $types[] = $type;

      if(!$can_be_multi)
        break;

      if($this->T != ord(','))
        break;
      $this->_nextT();
    }

    if(sizeof($types) > 1)
      return new mtgTypeRef(new mtgMultiType($types), $this->_scope(), new mtgOrigin($this->file, $this->line));
    else
      return $types[0];
  }

  private function _parseFuncType()
  {
    $ftype = new mtgMetaFunc('');

    $this->_nextT();

    $this->_checkThenNext(ord('('));

    $c = 0;
    while(true)
    {
      if($this->T == ord(')'))
      {
        $this->_nextT();
        break;
      }
      else if($c > 0)
      {
        $this->_checkThenNext(ord(','));
      }

      $arg_type = $this->_parseType();
      $c++;
      $arg = new mtgMetaField("_$c", $arg_type);
      $ftype->addArg($arg);
    }

    if($this->T == ord(':'))
    {
      $this->_nextT();
      $ret_type = $this->_parseType(true/*can be multi-type*/);
      $ftype->setReturnType($ret_type);
    }
    return $ftype;
  }

  private function _resolveIncludes(mtgMetaParsedModule $module, string &$text)
  { 
    $include_paths = $this->config['include_path'];

    $result = array();
    $lines = explode("\n", $text);
    foreach($lines as $line)
    {
      if(preg_match('~^#include\s+(\S+)~', $line, $m))
      {
        $this->_processInclude($module, $m[1], $include_paths);
        $result[] = "";
      }
      else
        $result[] = $line;
    }
    $text = implode("\n", $result);
  }

  private function _processInclude(mtgMetaParsedModule $module, string $include, array $include_paths)
  {
    $file = false;
    foreach($include_paths as $include_path)
    {
      $file = realpath($include_path . "/" . $include);
      if($file !== false)
        break;
    }

    if($file === false)
      throw new Exception("#include {$include} can't be resolved(include path is '". implode(':', $include_paths) . "')");

    $this->_parseInclude($module, $file);
  }

  private function _parseEnumOrValues()
  {
    $values = array();
    while(true)
    {
      if($this->T == self::T_UserSymbol)          
      {
        $values[] = $this->T_value;
        $this->_nextT();
        if(!$this->_nextIf(ord('|')))
          break;
      }
      else
        break;
    }

    return $values;
  }

  private function _parseEnum($is_global = true)
  {
    $this->_nextT();
    $name = $this->_parseDotName();

    $this->_checkThenNext(ord('{'));

    $enum = new mtgMetaEnum($name);
    $tokens = $this->shared_tokens;
    if($this->T == self::T_Prop)
      $tokens = array_merge($tokens, $this->_parsePropTokens());
    $enum->setTokens($tokens);

    $or_values = array();
    while(true)
    {
      if($this->_nextIf(ord('}')))
        break;
      $key = $this->T_value;
      $this->_checkThenNext(self::T_UserSymbol);
      $this->_checkThenNext(ord('='));
      if($this->T == self::T_UserSymbol)
      {
        $or_values[$key] = $this->_parseEnumOrValues();
      }
      else
      {
        $value = $this->T_value;
        $this->_checkThenNext(self::T_IntegerConstant);
        $enum->addValue($key, $value);
      }
    }
    $enum->addOrValues($or_values);

    //NOTE: special case for enums when we allow to 'override' the original one, 
    //      with additional values 
    if($enum->hasToken('enum_override'))
    {
      if(!$is_global)
        $this->_error("Override supported for global enums only");

      $existing = $this->current_meta->findUnit($enum->getMetaId());
      if(!$existing)
        throw new Exception("Not found '{$name}' enum to override values");
      if(!($existing->object instanceof mtgMetaEnum))
        throw new Exception("Not an enum struct '{$name}'");

      $existing->object->override($enum);
    }
    //NOTE: special case for enums when we allow to 'replace' the original one, 
    //      with additional values 
    else if($enum->hasToken('enum_replace'))
    {
      if(!$is_global)
        $this->_error("Replace supported for global enums only");

      $existing = $this->current_meta->findUnit($enum->getMetaId());
      if(!$existing)
        throw new Exception("Not found '{$name}' enum to replace values");
      if(!($existing->object instanceof mtgMetaEnum))
        throw new Exception("Not an enum struct '{$name}'");

      $existing->object->replace($enum);
    }
    else if($is_global)
      $this->_addUnit(new mtgMetaInfoUnit($this->module, $enum));

    return $enum;
  }

  static private function _isBuiltinType(int $t) : bool
  {
    return $t > self::T_MinType && $t < self::T_MaxType;
  }

  private function _pushScope(mtgScope $scope)
  {
    $this->scopes[] = $scope;
  }

  private function _popScope()
  {
    array_shift($this->scopes);
  }

  private function _scope() : mtgScope
  {
    if(!$this->scopes)
      return $this->module;

    return $this->scopes[count($this->scopes)-1];
  }

  private function _parseFields(callable $next_doer)
  {
    $flds = array();

    while(true)
    {
      if($next_doer())
        break;

      if($this->T == self::T_UserSymbol)
      {
        $name = $this->T_value;
        $this->_nextT();
        $this->_checkThenNext(ord(':'));

        if($this->T == self::T_UserSymbol || 
          $this->T == self::T_Func ||
          self::_isBuiltinType($this->T))
        {
          $type = $this->_parseType();

          $fld = new mtgMetaField($name, $type);

          if($this->T == self::T_Prop)
            $fld->setTokens($this->_parsePropTokens());

          $flds[] = $fld;
        }
        else
          $this->_error("Type expected");
      }
      else
        $this->_error("Unexpected fields symbol");
    }

    return $flds;
  }

  private function _parseFuncs()
  {
    $end_token = ord('}');

    $funcs = array();

    while(true)
    {
      $fn = $this->_parseFunc();
      $funcs[] = $fn;

      if($this->T == $end_token)
      {
        $this->_nextT();
        break;
      }
      
      $this->_nextT();
    }

    return $funcs;
  }

  private function _parseDotName() : string
  {
    $dot_name = '';

    while(true)
    {
      if($this->T != self::T_UserSymbol)
        $this->_error("Unexpected name symbol");
      
      $dot_name .= $this->T_value;
      $this->_nextT();
      if($this->T != ord('.'))
        break;
      $dot_name .= '.';
      $this->_nextT();
    }

    return $dot_name;
  }

  private function _parseFunc() : mtgMetaFunc
  {
    $name = $this->_parseDotName();
    $fn = new mtgMetaFunc($name);

    $this->_checkThenNext(ord('('));
    if($this->T == self::T_Prop)
      $fn->setTokens($this->_parsePropTokens());
    $args = $this->_parseFields(function() 
      { return $this->_nextIf(ord(')')); } 
    );
    $fn->setArgs($args);

    $ret_type = null;
    if($this->T == ord(':'))
    {
      $this->_nextT();
      if($this->T == self::T_UserSymbol ||
         $this->T == self::T_Func ||
        self::_isBuiltinType($this->T))
      {
        $ret_type = $this->_parseType(true/*can be multi-type*/);
        $fn->setReturnType($ret_type);
      }
      else
        $this->_error("Unexpected func type");
    }

    return $fn;
  }

  private function _addUnit(mtgMetaInfoUnit $unit)
  {
    $this->current_meta->addUnit($unit);
    $this->module->addUnit($unit);
  }

  private function _parseFreeFunc()
  {
    $this->_nextT();
    $fn = $this->_parseFunc();
    $fn->setTokens(array_merge($this->shared_tokens, $fn->getTokens()));
    $this->_addUnit(new mtgMetaInfoUnit($this->module, $fn));
  }

  private function _parseStruct()
  {
    $this->_nextT();
    $struct_origin = new mtgOrigin($this->file, $this->line);
    $name = $this->_parseDotName();

    $parent = null;
    if($this->T == self::T_Extends)
    {
      $this->_nextT();
      $origin = new mtgOrigin($this->file, $this->line);
      $parent_name = $this->_parseDotName();
      $parent = new mtgTypeRef($parent_name, $this->_scope(), $origin);
    }

    $implements = array();
    if($this->T == self::T_Implements)
    {
      do 
      {
        $this->_nextT();
        $origin = new mtgOrigin($this->file, $this->line);
        $if_name = $this->_parseDotName();
        $implements[] = new mtgTypeRef($if_name, $this->_scope(), $origin);
      } while($this->T == ord(','));
    }

    $this->_checkThenNext(ord('{'));

    $s = new mtgMetaStruct($name, array(), $parent, array(), $implements);
    $s->setOrigin($struct_origin);
    $this->_addUnit(new mtgMetaInfoUnit($this->module, $s));

    $tokens = $this->shared_tokens;
    if($this->T == self::T_Prop)
      $tokens = array_merge($tokens, $this->_parsePropTokens());
    $s->setTokens($tokens);

    $seen_funcs = false;
    $flds = $this->_parseFields(
      function() use(&$seen_funcs) 
      { 
        if($this->_nextIf(ord('}')))
          return true;
        if($this->_nextIf(self::T_Func)) 
        {
          $seen_funcs = true;
          return true;
        }
      }
    );
    foreach($flds as $fld)
      $s->addField($fld);

    if($seen_funcs)
    {
      $funcs = $this->_parseFuncs();
      foreach($funcs as $fn)
        $s->addFunc($fn);
    }
  }

  private function _parseInterface()
  {
    $this->_nextT();
    $name = $this->_parseDotName();

    $s = new mtgMetaInterface($name);
    $this->_addUnit(new mtgMetaInfoUnit($this->module, $s));

    $tokens = $this->shared_tokens;
    if($this->T == self::T_Prop)
      $tokens = array_merge($tokens, $this->_parsePropTokens());
    $s->setTokens($tokens);

    if($this->T !== ord('}'))
    {
      $this->_nextT();
      $funcs = $this->_parseFuncs();
      foreach($funcs as $fn)
        $s->addFunc($fn);
    }
    else
      $this->_nextT();
  }

  private function _parseRPC($is_global = true)
  {
    $this->_nextT();
    $code = $this->T_value;
    $this->_checkThenNext(self::T_IntegerConstant);
    $name = $this->_parseDotName();
    $this->_checkThenNext(ord('('));

    $tokens = $this->shared_tokens;
    if($this->T == self::T_Prop)
      $tokens = array_merge($tokens, $this->_parsePropTokens());

    $req_fields = $this->_parseFields(function() 
      { return $this->_nextIf(ord(')')); } 
    );

    $this->_checkThenNext(ord('{'));

    $rsp_fields = $this->_parseFields(function() 
      { return $this->_nextIf(ord('}')); } 
    );

    $req = new mtgMetaPacket($code, $is_global ? "RPC_REQ_$name" : "Request");
    $req->setFields($req_fields);
    $rsp = new mtgMetaPacket($code, $is_global ? "RPC_RSP_$name" : "Response");
    $rsp->setFields($rsp_fields);

    $rpc = new mtgMetaRPC($is_global ? "RPC_$name" : $name, $code, $req, $rsp, $tokens);

    if($is_global)
      $this->_addUnit(new mtgMetaInfoUnit($this->module, $rpc));

    return $rpc;
  }

  private function _parseService()
  {
    $this->_nextT();
    $name = $this->_parseDotName();

    $this->_checkThenNext(ord('{'));

    $service = new mtgMetaService($name, $this->_scope());
    $this->_pushScope($service);

    $tokens = $this->shared_tokens;
    if($this->T == self::T_Prop)
      $tokens = array_merge($tokens, $this->_parsePropTokens());
    $service->setTokens($tokens);

    while(true)
    {
      if($this->_nextIf(ord('}')))
        break;
      $key = $this->T_value;
      if($this->T == self::T_RPC)
        $service->addRPC($this->_parseRPC(false));
      else if($this->T == self::T_Enum)
        $service->addUserType($this->_parseEnum(false));
      else
        $this->_error("Unsupported type");
    }

    $this->_popScope();

    $this->_addUnit(new mtgMetaInfoUnit($this->module, $service));
  }

  private function _parsePropTokens() : array
  {
    $prop_tokens = array();

    while(true)
    {
      if($this->T != self::T_Prop)
        break;

      $name = ltrim($this->T_value, '@');
      $this->_validatePropToken($name);
      $this->_nextT();

      $value = null;
      if($this->T == ord(':'))
      {
        //let's read the value
        while(true)
        {
          //TODO: The code below is ugly and must be heavily refactored,
          //      it just tries to be convenient and keep BC: any token property
          //      value can have almost any kind of symbols excluding new line. 
          //      In the future we should restrict property values to certain types only
          $this->_nextT(true/*stop on new line*/);

          if($this->T == ord("\n"))
          {
            $this->_nextT();
            break;
          }
          else if($this->T == self::T_Prop)
          {
            break;
          }
          else
          {
            $tmp = $this->T_value; 
            if($this->T == self::T_StringConstant)
              $tmp = "\"$tmp\"";
            if($value === null)
              $value = '';
            $value .= $tmp;
          }
        }
      }

      $prop_tokens[$name] = $value;
    }
    return $prop_tokens;
  }

  private function _validatePropToken(string $name)
  {
    if(!isset($this->config['valid_tokens']) || 
       !is_array($this->config['valid_tokens']))
      return;

    if(!in_array($name, $this->config['valid_tokens']))
      throw new Exception("Unknown property token '@$name'");
  }

  private function _nextT(bool $stop_on_new_line = false)
  {
    while(true)
    {
      $c = $this->cursor_char;

      //setting default values
      $this->T = ord($c);
      $this->T_value = $c;

      //NOTE: current 'cursor_pos' is ahead of 'c' by one character
      $this->_cursorNext();

      switch($c)
      {
        case '': $this->T = self::T_EOF; return;
        case "\n": if($stop_on_new_line) return; else break;
        case ' ': case "\r": case "\t": break;
        case '{': case '}': case '(': case ')': case '[': case ']': case '|': return;
        case ',': case ':': case ';': case '=': return;
        case '.':
          if(!ctype_digit($this->cursor_char)) 
            return;
          $this->_error("Floating point constant can't start with .");
          break;
        case '"':
          $this->T_value = '';
          while($this->cursor_char != '"') 
          {
            if(ord($this->cursor_char) < ord(' '))
              $this->_error("Illegal character in string constant");
            if($this->cursor_char == '\\') 
            {
              $this->_cursorNext();
              switch($this->cursor_char) 
              {
                case 'n':  $this->T_value .= "\n"; $this->_cursorNext(); break;
                case 't':  $this->T_value .= "\t"; $this->_cursorNext(); break;
                case 'r':  $this->T_value .= "\r"; $this->_cursorNext(); break;
                case '"': $this->T_value .= '"'; $this->_cursorNext(); break;
                case '\\': $this->T_value .= '\\'; $this->_cursorNext(); break;
                default: $this->_error("Unknown escape code in string constant"); break;
              }
            }
            else // printable chars + UTF-8 bytes
            {
              $this->T_value .= $this->cursor_char;
              $this->_cursorNext();
            }
          }
          $this->T = self::T_StringConstant;
          $this->_cursorNext();
          return;

        case '`':
          $this->T_value = '';
          //TODO: code below is not robust enough
          while($this->cursor_char != '`') 
          {
            $this->T_value .= $this->cursor_char;
            $this->_cursorNext();
          }
          $this->T = self::T_RawStringConstant;
          $this->_cursorNext();
          return;

        case '/':
          if($this->cursor_char == '/') 
          {
            $this->_cursorNext();
            //@phpstan-ignore-next-line
            while($this->cursor_char != '' && $this->cursor_char != "\n") 
              $this->_cursorNext();
            //@phpstan-ignore-next-line
            break;
          }

        case '#':
          while($this->cursor_char != '' && $this->cursor_char != "\n")
            $this->_cursorNext(); 
          break;

        case '@':
          $start = $this->cursor_pos - 1;
          while(ctype_alnum($this->cursor_char) || $this->cursor_char == '_')
            $this->_cursorNext(); 

          $this->T = self::T_Prop;
          $this->T_value = substr($this->source, $start, $this->cursor_pos - $start);
          return;

        default:

          //symbols
          if(ctype_alpha($c))
          {
            //collect all chars of an identifier
            $start = $this->cursor_pos - 1;
            while(ctype_alnum($this->cursor_char) || $this->cursor_char == '_')
              $this->_cursorNext();
            $this->T_value = substr($this->source, $start, $this->cursor_pos - $start);

            if(isset($this->symbol2T[$this->T_value]))
              $this->T = $this->symbol2T[$this->T_value];
            else //otherwise it's assumed to be a user defined symbol
              $this->T = self::T_UserSymbol;

            return;
          }
          //digits
          else if(ctype_digit($c) || $c == '-')
          {
            $start = $this->cursor_pos - 1;
            while(ctype_digit($this->cursor_char)) 
              $this->_cursorNext();
            if($this->cursor_char == '.')
            {
              $this->_cursorNext();
              while(ctype_digit($this->cursor_char)) 
                $this->_cursorNext();
              // see if this float has a scientific notation suffix. Both JSON
              // and C++ (through strtod() we use) have the same format:
              //@phpstan-ignore-next-line
              if($this->cursor_char == 'e' || $this->cursor_char == 'E') 
              {
                $this->_cursorNext();
                if($this->cursor_char == '+' || $this->cursor_char == '-') 
                  $this->_cursorNext();
                while(ctype_digit($this->cursor_char)) 
                  $this->_cursorNext();
              }
              $this->T = self::T_FloatConstant;
            }
            else
              $this->T = self::T_IntegerConstant;
            $this->T_value = substr($this->source, $start, $this->cursor_pos - $start);
            return;
          }

          $this->_error("Illegal character '$c'");
      }
    }
  }

  private function _cursorNext()
  {
    ++$this->cursor_pos;
    $this->cursor_char = substr($this->source, $this->cursor_pos, 1);
    if($this->cursor_char === "\n") 
      $this->line++;
    //EOF
    if($this->cursor_char === '' || 
      //keeping BC with substr(..) before php 8.0 
      //@phpstan-ignore-next-line
      is_bool($this->cursor_char))
    {
      $this->cursor_char = '';
    }
  }

  private function _nextIf(int $t) : bool
  {
    $yes = $t === $this->T;
    if($yes)
      $this->_nextT();
    return $yes;
  }

  private function _checkThenNext(int $t)
  {
    if($t !== $this->T)
      $this->_error("Expecting '" . $this->_toStr($t) . "' instead got '" . $this->_toStr($this->T) . "'");
    $this->_nextT();
  }

  private function _toStr(int $t) : string
  {
    if($t < self::T_NonOrdMark)
      return chr($t);
    return $this->T2descr[$t];
  }

  private function _error(string $msg)
  {
    throw new Exception($msg . " ('{$this->T_value}', {$this->T})");
  }
}