How to use

parseLookaheadOperator

method

in

org.matheclipse.parser.client.Parser

private final ASTNode parsePrefixOperator(final PrefixOperator prefixOperator) {
  getNextToken();
  final ASTNode temp = parseLookaheadOperator(prefixOperator.getPrecedence());
  if ("PreMinus".equals(prefixOperator.getFunctionName()) && temp instanceof NumberNode) {
    // special cases for negative numbers
    ((NumberNode) temp).toggleSign();
    return temp;
  }
  return prefixOperator.createFunction(fFactory, temp);
}

private final ASTNode parseInfixOperator(ASTNode lhs, InfixOperator infixOperator) {
  ASTNode rhs;
  rhs = parseLookaheadOperator(infixOperator.getPrecedence());
  lhs = infixOperator.createFunction(fFactory, lhs, rhs);
  String infixOperatorString = infixOperator.getOperatorString();
  while (fToken == TT_OPERATOR && infixOperator.getGrouping() == InfixOperator.NONE
      && infixOperatorString.equals(fOperatorString)) {
    getNextToken();
    if (";".equals(infixOperatorString)) {
      if (fToken == TT_EOF || fToken == TT_ARGUMENTS_CLOSE || fToken == TT_LIST_CLOSE
          || fToken == TT_PRECEDENCE_CLOSE || fToken == TT_COMMA) {
        ((FunctionNode) lhs).add(fFactory.createSymbol("Null"));
        break;
      }
    }
    while (fToken == TT_NEWLINE) {
      getNextToken();
    }
    rhs = parseLookaheadOperator(infixOperator.getPrecedence());
    ((FunctionNode) lhs).add(rhs);
  }
  return lhs;
}

private ASTNode parsePrimary() {
  if (fToken == TT_OPERATOR) {
    if (fOperatorString.equals(".")) {
      fCurrentChar = '.';
      return getNumber(false);
    }
    final PrefixOperator prefixOperator = determinePrefixOperator();
    if (prefixOperator != null) {
      getNextToken();
      final ASTNode temp = parseLookaheadOperator(prefixOperator.getPrecedence());
      if (prefixOperator.getFunctionName().equals("PreMinus")) {
        // special cases for negative numbers
        if (temp instanceof NumberNode) {
          ((NumberNode) temp).toggleSign();
          return temp;
        }
      }
      return prefixOperator.createFunction(fFactory, temp);
    }
    throwSyntaxError("Operator: " + fOperatorString + " is no prefix operator.");
  }
  return getPart();
}

/**
 * Parses the primary.
 * 
 * @return the AST node
 */
private ASTNode parsePrimary() {
  if ( fToken == TT_OPERATOR ) {
    final PrefixOperator prefixOperator = determinePrefixOperator();
    if ( prefixOperator != null ) {
      getNextToken();
      final ASTNode temp = parseLookaheadOperator( prefixOperator.getPrecedence() );
      if ( prefixOperator.getFunctionName().equals( "PreMinus" ) ) {
        // special cases for negative numbers
        if ( temp instanceof NumberNode ) {
          ((NumberNode) temp).toggleSign();
          return temp;
        }
      }
      return prefixOperator.createFunction( fFactory, temp );
    }
    throwSyntaxError( "Operator: " + fOperatorString + " is no prefix operator." );
  }
  return getPart();
}

rhs = parseLookaheadOperator( oper.getPrecedence() );
lhs = fFactory.createFunction( fFactory.createSymbol( oper.getFunctionName() ), lhs, rhs );
lhs = parseArguments( lhs );
if ( infixOperator.getPrecedence() >= min_precedence ) {
  getNextToken();
  rhs = parseLookaheadOperator( infixOperator.getPrecedence() );
  lhs = infixOperator.createFunction( fFactory, lhs, rhs );
  lhs = parseArguments( lhs );

rhs = parseLookaheadOperator(oper.getPrecedence());
lhs = fFactory.createFunction(fFactory.createSymbol(oper.getFunctionName()), lhs, rhs);
lhs = parseArguments(lhs);
if (infixOperator.getPrecedence() >= min_precedence) {
  getNextToken();
  rhs = parseLookaheadOperator(infixOperator.getPrecedence());
  lhs = infixOperator.createFunction(fFactory, lhs, rhs);
  lhs = parseArguments(lhs);

rhs = parseLookaheadOperator(oper.getPrecedence());
lhs = fFactory.createFunction(fFactory.createSymbol(oper.getFunctionName()), lhs, rhs);
continue;