ExpressionParser2.h

/*
 * GDevelop Core
 * Copyright 2008-present Florian Rival ([email protected]). All rights
 * reserved. This project is released under the MIT License.
 */
#ifndef GDCORE_EXPRESSIONPARSER2_H
#define GDCORE_EXPRESSIONPARSER2_H
 
#include <memory>
#include <utility>
#include <vector>
 
#include "ExpressionParser2Node.h"
#include "GDCore/Extensions/Metadata/ExpressionMetadata.h"
#include "GDCore/Extensions/Metadata/MetadataProvider.h"
#include "GDCore/Extensions/Metadata/ObjectMetadata.h"
#include "GDCore/Project/Layout.h"  // For GetTypeOfObject and GetTypeOfBehavior
#include "GDCore/String.h"
#include "GDCore/Tools/Localization.h"
#include "GDCore/Tools/MakeUnique.h"
#include "GrammarTerminals.h"
namespace gd {
class Expression;
class ObjectsContainer;
class Platform;
class ParameterMetadata;
class ExpressionMetadata;
}  // namespace gd
 
namespace gd {
 
using namespace gd::GrammarTerminals;
 
class GD_CORE_API ExpressionParser2 {
 public:
  ExpressionParser2();
  virtual ~ExpressionParser2(){};
 
  std::unique_ptr<ExpressionNode> ParseExpression(
      const gd::String &expression_) {
    expression = expression_;
 
    currentPosition = 0;
    return Start();
  }
 
  static size_t WrittenParametersFirstIndex(const gd::String &objectName,
                                            const gd::String &behaviorName) {
    // By convention, object is always the first parameter, and behavior the
    // second one.
    return !behaviorName.empty() ? 2 : (!objectName.empty() ? 1 : 0);
  }
 
 private:
  std::unique_ptr<ExpressionNode> Start() {
    size_t expressionStartPosition = GetCurrentPosition();
    auto expression = Expression();
 
    // Check for extra characters at the end of the expression
    if (!IsEndReached()) {
      auto op = gd::make_unique<OperatorNode>(' ');
      op->leftHandSide = std::move(expression);
      op->rightHandSide = ReadUntilEnd();
      op->rightHandSide->parent = op.get();
 
      op->rightHandSide->diagnostic = RaiseSyntaxError(
          _("The expression has extra character at the end that should be "
            "removed (or completed if your expression is not finished)."));
 
      op->location = ExpressionParserLocation(expressionStartPosition,
                                              GetCurrentPosition());
      return std::move(op);
    }
 
    return expression;
  }
 
  std::unique_ptr<ExpressionNode> Expression() {
    SkipAllWhitespaces();
 
    size_t expressionStartPosition = GetCurrentPosition();
    std::unique_ptr<ExpressionNode> leftHandSide = Term();
 
    SkipAllWhitespaces();
 
    if (IsEndReached()) return leftHandSide;
    if (CheckIfChar(IsExpressionEndingChar)) return leftHandSide;
    if (CheckIfChar(IsExpressionOperator)) {
      auto op = gd::make_unique<OperatorNode>(GetCurrentChar());
      op->leftHandSide = std::move(leftHandSide);
      op->leftHandSide->parent = op.get();
      op->diagnostic = ValidateOperator(GetCurrentChar());
      SkipChar();
      op->rightHandSide = Expression();
      op->rightHandSide->parent = op.get();
 
      op->location = ExpressionParserLocation(expressionStartPosition,
                                              GetCurrentPosition());
      return std::move(op);
    }
 
    leftHandSide->diagnostic = RaiseSyntaxError(
        "More than one term was found. Verify that your expression is "
        "properly written.");
 
    auto op = gd::make_unique<OperatorNode>(' ');
    op->leftHandSide = std::move(leftHandSide);
    op->leftHandSide->parent = op.get();
    op->rightHandSide = Expression();
    op->rightHandSide->parent = op.get();
    op->location =
        ExpressionParserLocation(expressionStartPosition, GetCurrentPosition());
    return std::move(op);
  }
 
  std::unique_ptr<ExpressionNode> Term() {
    SkipAllWhitespaces();
 
    size_t expressionStartPosition = GetCurrentPosition();
    std::unique_ptr<ExpressionNode> factor = Factor();
 
    SkipAllWhitespaces();
 
    // This while loop is used instead of a recursion (like in Expression)
    // to guarantee the proper operator precedence. (Expression could also
    // be reworked to use a while loop).
    while (CheckIfChar(IsTermOperator)) {
      auto op = gd::make_unique<OperatorNode>(GetCurrentChar());
      op->leftHandSide = std::move(factor);
      op->leftHandSide->parent = op.get();
      op->diagnostic = ValidateOperator(GetCurrentChar());
      SkipChar();
      op->rightHandSide = Factor();
      op->rightHandSide->parent = op.get();
      op->location = ExpressionParserLocation(expressionStartPosition,
                                              GetCurrentPosition());
      SkipAllWhitespaces();
 
      factor = std::move(op);
    }
 
    return factor;
  };
 
  std::unique_ptr<ExpressionNode> Factor() {
    SkipAllWhitespaces();
    size_t expressionStartPosition = GetCurrentPosition();
 
    if (CheckIfChar(IsQuote)) {
      std::unique_ptr<ExpressionNode> factor = ReadText();
      return factor;
    } else if (CheckIfChar(IsUnaryOperator)) {
      auto unaryOperatorCharacter = GetCurrentChar();
      SkipChar();
 
      auto operatorOperand = Factor();
 
      auto unaryOperator = gd::make_unique<UnaryOperatorNode>(
          unaryOperatorCharacter);
      unaryOperator->diagnostic = ValidateUnaryOperator(
          unaryOperatorCharacter, expressionStartPosition);
      unaryOperator->factor = std::move(operatorOperand);
      unaryOperator->factor->parent = unaryOperator.get();
      unaryOperator->location = ExpressionParserLocation(
          expressionStartPosition, GetCurrentPosition());
 
      return std::move(unaryOperator);
    } else if (CheckIfChar(IsNumberFirstChar)) {
      std::unique_ptr<ExpressionNode> factor = ReadNumber();
      return factor;
    } else if (CheckIfChar(IsOpeningParenthesis)) {
      size_t expressionStartPosition = GetCurrentPosition();
      SkipChar();
 
      // The expression inside the parentheses excluding them.
      auto expression = Expression();
 
      // The expression and its parentheses.
      auto factor = gd::make_unique<SubExpressionNode>(std::move(expression));
 
      if (!CheckIfChar(IsClosingParenthesis)) {
        factor->diagnostic =
            RaiseSyntaxError(_("Missing a closing parenthesis. Add a closing "
                               "parenthesis for each opening parenthesis."));
      }
      SkipIfChar(IsClosingParenthesis);
      factor->location = ExpressionParserLocation(expressionStartPosition,
                                                  GetCurrentPosition());
 
      return std::move(factor);
    } else if (CheckIfChar(IsAllowedInIdentifier)) {
      return Identifier();
    }
 
    std::unique_ptr<ExpressionNode> factor = ReadUntilWhitespace();
    return factor;
  }
 
  std::unique_ptr<IdentifierOrFunctionCallOrObjectFunctionNameOrEmptyNode>
  Identifier() {
    auto identifierAndLocation = ReadIdentifierName();
    gd::String name = identifierAndLocation.name;
    auto nameLocation = identifierAndLocation.location;
 
    SkipAllWhitespaces();
 
    // We consider a namespace separator to be allowed here and be part of the
    // function name (or object name, but object names are not allowed to
    // contain a ":"). This is because functions from extensions have their
    // extension name prefix, and separated by the namespace separator. This
    // could maybe be refactored to create different nodes in the future.
    if (IsNamespaceSeparator()) {
      SkipNamespaceSeparator();
      SkipAllWhitespaces();
 
      auto postNamespaceIdentifierAndLocation = ReadIdentifierName();
      name += NAMESPACE_SEPARATOR;
      name += postNamespaceIdentifierAndLocation.name;
      ExpressionParserLocation completeNameLocation(
          nameLocation.GetStartPosition(),
          postNamespaceIdentifierAndLocation.location.GetEndPosition());
      nameLocation = completeNameLocation;
    }
 
    if (CheckIfChar(IsOpeningParenthesis)) {
      ExpressionParserLocation openingParenthesisLocation = SkipChar();
      return FreeFunction(name, nameLocation, openingParenthesisLocation);
    } else if (CheckIfChar(IsDot)) {
      ExpressionParserLocation dotLocation = SkipChar();
      SkipAllWhitespaces();
      return ObjectFunctionOrBehaviorFunctionOrVariable(
          name, nameLocation, dotLocation);
    } else if (CheckIfChar(IsOpeningSquareBracket)) {
      return Variable(name, nameLocation);
    } else {
      auto identifier = gd::make_unique<IdentifierNode>(name);
      identifier->location = ExpressionParserLocation(
          nameLocation.GetStartPosition(), GetCurrentPosition());
      identifier->identifierNameLocation = identifier->location;
      return std::move(identifier);
    }
  }
 
  std::unique_ptr<VariableNode> Variable(const gd::String &name, gd::ExpressionParserLocation nameLocation) {
    auto variable = gd::make_unique<VariableNode>(name);
 
    if (CheckIfChar(IsOpeningSquareBracket) || CheckIfChar(IsDot)) {
      variable->child = VariableAccessorOrVariableBracketAccessor();
      variable->child->parent = variable.get();
    }
 
    variable->location = ExpressionParserLocation(
        nameLocation.GetStartPosition(), GetCurrentPosition());
    variable->nameLocation = nameLocation;
    return std::move(variable);
  }
 
  std::unique_ptr<VariableAccessorOrVariableBracketAccessorNode>
  VariableAccessorOrVariableBracketAccessor() {
    size_t childStartPosition = GetCurrentPosition();
 
    SkipAllWhitespaces();
    if (CheckIfChar(IsOpeningSquareBracket)) {
      SkipChar();
      auto child = gd::make_unique<VariableBracketAccessorNode>(Expression());
      child->expression->parent = child.get();
 
      if (!CheckIfChar(IsClosingSquareBracket)) {
        child->diagnostic =
            RaiseSyntaxError(_("Missing a closing bracket. Add a closing "
                               "bracket for each opening bracket."));
      }
      SkipIfChar(IsClosingSquareBracket);
 
      SkipAllWhitespaces();
      if (CheckIfChar(IsOpeningSquareBracket) || CheckIfChar(IsDot)) {
        child->child = VariableAccessorOrVariableBracketAccessor();
        child->child->parent = child.get();
      }
      child->location =
          ExpressionParserLocation(childStartPosition, GetCurrentPosition());
 
      return std::move(child);
    } else if (CheckIfChar(IsDot)) {
      auto dotLocation = SkipChar();
      SkipAllWhitespaces();
 
      auto identifierAndLocation = ReadIdentifierName(/*allowDeprecatedSpacesInName=*/ false);
      auto child =
          gd::make_unique<VariableAccessorNode>(identifierAndLocation.name);
      if (identifierAndLocation.name.empty()) {
        child->diagnostic = RaiseSyntaxError(_("A name should be entered after the dot."));
      }
 
      SkipAllWhitespaces();
      if (CheckIfChar(IsOpeningSquareBracket) || CheckIfChar(IsDot)) {
        child->child = VariableAccessorOrVariableBracketAccessor();
        child->child->parent = child.get();
      }
      child->nameLocation = identifierAndLocation.location;
      child->dotLocation = dotLocation;
      child->location =
          ExpressionParserLocation(childStartPosition, GetCurrentPosition());
 
      return std::move(child);
    }
 
    // Should never happen, unless a node called this function without checking if the current character
    // was a dot or an opening bracket - this means there is an error in the grammar.
    auto unrecognisedNode = gd::make_unique<VariableAccessorOrVariableBracketAccessorNode>();
    unrecognisedNode->diagnostic = RaiseSyntaxError(_("A dot or bracket was expected here."));
    return std::move(unrecognisedNode);
  }
 
  std::unique_ptr<FunctionCallNode> FreeFunction(
      const gd::String &functionFullName,
      const ExpressionParserLocation &identifierLocation,
      const ExpressionParserLocation &openingParenthesisLocation) {
    // TODO: error if trying to use function for type != "number" && != "string"
    // + Test for it
 
    auto function =
        gd::make_unique<FunctionCallNode>(functionFullName);
    auto parametersNode = Parameters(function.get());
    function->parameters = std::move(parametersNode.parameters);
    function->diagnostic = std::move(parametersNode.diagnostic);
 
    function->location = ExpressionParserLocation(
        identifierLocation.GetStartPosition(), GetCurrentPosition());
    function->functionNameLocation = identifierLocation;
    function->openingParenthesisLocation = openingParenthesisLocation;
    function->closingParenthesisLocation =
        parametersNode.closingParenthesisLocation;
 
    return std::move(function);
  }
 
  std::unique_ptr<IdentifierOrFunctionCallOrObjectFunctionNameOrEmptyNode>
  ObjectFunctionOrBehaviorFunctionOrVariable(
      const gd::String &parentIdentifier,
      const ExpressionParserLocation &parentIdentifierLocation,
      const ExpressionParserLocation &parentIdentifierDotLocation) {
    auto childIdentifierAndLocation = ReadIdentifierName(/*allowDeprecatedSpacesInName=*/ false);
    const gd::String &childIdentifierName = childIdentifierAndLocation.name;
    const auto &childIdentifierNameLocation =
        childIdentifierAndLocation.location;
 
    std::unique_ptr<gd::ExpressionParserError> emptyNameError = childIdentifierName.empty() ?
      RaiseSyntaxError(_("A name should be entered after the dot.")) : nullptr;
 
    SkipAllWhitespaces();
 
    if (IsNamespaceSeparator()) {
      ExpressionParserLocation namespaceSeparatorLocation =
          SkipNamespaceSeparator();
      SkipAllWhitespaces();
      auto behaviorFunction = BehaviorFunction(parentIdentifier,
                              childIdentifierName,
                              parentIdentifierLocation,
                              parentIdentifierDotLocation,
                              childIdentifierNameLocation,
                              namespaceSeparatorLocation);
 
      if (emptyNameError) behaviorFunction->diagnostic = std::move(emptyNameError);
      return std::move(behaviorFunction);
    } else if (CheckIfChar(IsOpeningParenthesis)) {
      ExpressionParserLocation openingParenthesisLocation = SkipChar();
 
      auto function = gd::make_unique<FunctionCallNode>(
          parentIdentifier,
          childIdentifierName);
      auto parametersNode = Parameters(function.get(), parentIdentifier);
      function->parameters = std::move(parametersNode.parameters),
      function->diagnostic = emptyNameError ? std::move(emptyNameError) : std::move(parametersNode.diagnostic);
 
      function->location = ExpressionParserLocation(
          parentIdentifierLocation.GetStartPosition(), GetCurrentPosition());
      function->objectNameLocation = parentIdentifierLocation;
      function->objectNameDotLocation = parentIdentifierDotLocation;
      function->functionNameLocation = childIdentifierNameLocation;
      function->openingParenthesisLocation = openingParenthesisLocation;
      function->closingParenthesisLocation =
          parametersNode.closingParenthesisLocation;
      return std::move(function);
    } else if (CheckIfChar(IsDot) || CheckIfChar(IsOpeningSquareBracket)) {
      auto variable = gd::make_unique<VariableNode>(parentIdentifier);
      variable->diagnostic = std::move(emptyNameError);
 
      auto child =
          gd::make_unique<VariableAccessorNode>(childIdentifierName);
      child->child = VariableAccessorOrVariableBracketAccessor();
      child->child->parent = child.get();
      child->nameLocation = childIdentifierNameLocation;
      child->dotLocation = parentIdentifierDotLocation;
      child->location = ExpressionParserLocation(
          parentIdentifierDotLocation.GetStartPosition(), GetCurrentPosition());
      variable->child = std::move(child);
      variable->child->parent = variable.get();
 
      variable->location = ExpressionParserLocation(
          parentIdentifierLocation.GetStartPosition(), GetCurrentPosition());
      variable->nameLocation = parentIdentifierLocation;
 
      return std::move(variable);
    }
 
    auto node = gd::make_unique<IdentifierNode>(
        parentIdentifier, childIdentifierName);
    node->location = ExpressionParserLocation(
        parentIdentifierLocation.GetStartPosition(), GetCurrentPosition());
    node->identifierNameLocation = parentIdentifierLocation;
    node->identifierNameDotLocation = parentIdentifierDotLocation;
    node->childIdentifierNameLocation = childIdentifierNameLocation;
    node->diagnostic = std::move(emptyNameError);
    return std::move(node);
  }
 
  std::unique_ptr<FunctionCallOrObjectFunctionNameOrEmptyNode> BehaviorFunction(
      const gd::String &objectName,
      const gd::String &behaviorName,
      const ExpressionParserLocation &objectNameLocation,
      const ExpressionParserLocation &objectNameDotLocation,
      const ExpressionParserLocation &behaviorNameLocation,
      const ExpressionParserLocation &behaviorNameNamespaceSeparatorLocation) {
    auto identifierAndLocation = ReadIdentifierName();
    const gd::String &functionName = identifierAndLocation.name;
    const auto &functionNameLocation = identifierAndLocation.location;
 
    SkipAllWhitespaces();
 
    if (CheckIfChar(IsOpeningParenthesis)) {
      ExpressionParserLocation openingParenthesisLocation = SkipChar();
 
      auto function = gd::make_unique<FunctionCallNode>(
          objectName,
          behaviorName,
          functionName);
      auto parametersNode =
          Parameters(function.get(), objectName, behaviorName);
      function->parameters = std::move(parametersNode.parameters);
      function->diagnostic = std::move(parametersNode.diagnostic);
 
      function->location = ExpressionParserLocation(
          objectNameLocation.GetStartPosition(), GetCurrentPosition());
      function->objectNameLocation = objectNameLocation;
      function->objectNameDotLocation = objectNameDotLocation;
      function->behaviorNameLocation = behaviorNameLocation;
      function->behaviorNameNamespaceSeparatorLocation =
          behaviorNameNamespaceSeparatorLocation;
      function->openingParenthesisLocation = openingParenthesisLocation;
      function->closingParenthesisLocation =
          parametersNode.closingParenthesisLocation;
      function->functionNameLocation = functionNameLocation;
      return std::move(function);
    } else {
      auto node = gd::make_unique<ObjectFunctionNameNode>(
          objectName, behaviorName, functionName);
      node->diagnostic = RaiseSyntaxError(
          _("An opening parenthesis was expected here to call a function."));
 
      node->location = ExpressionParserLocation(
          objectNameLocation.GetStartPosition(), GetCurrentPosition());
      node->objectNameLocation = objectNameLocation;
      node->objectNameDotLocation = objectNameDotLocation;
      node->objectFunctionOrBehaviorNameLocation = behaviorNameLocation;
      node->behaviorNameNamespaceSeparatorLocation =
          behaviorNameNamespaceSeparatorLocation;
      node->behaviorFunctionNameLocation = functionNameLocation;
      return std::move(node);
    }
  }
 
  // A temporary node that will be integrated into function nodes.
  struct ParametersNode {
    std::vector<std::unique_ptr<ExpressionNode>> parameters;
    std::unique_ptr<gd::ExpressionParserError> diagnostic;
    ExpressionParserLocation closingParenthesisLocation;
  };
 
  ParametersNode Parameters(
      FunctionCallNode *functionCallNode,
      const gd::String &objectName = "",
      const gd::String &behaviorName = "") {
    std::vector<std::unique_ptr<ExpressionNode>> parameters;
    gd::String lastObjectName = "";
 
    bool previousCharacterIsParameterSeparator = false;
    while (!IsEndReached()) {
      SkipAllWhitespaces();
 
      if (CheckIfChar(IsClosingParenthesis) && !previousCharacterIsParameterSeparator) {
        auto closingParenthesisLocation = SkipChar();
        return ParametersNode{
            std::move(parameters), nullptr, closingParenthesisLocation};
      }
      bool isEmptyParameter = CheckIfChar(IsParameterSeparator)
          || (CheckIfChar(IsClosingParenthesis) && previousCharacterIsParameterSeparator);
      auto parameter = isEmptyParameter ? gd::make_unique<EmptyNode>() : Expression();
      parameter->parent = functionCallNode;
      parameters.push_back(std::move(parameter));
 
      SkipAllWhitespaces();
      previousCharacterIsParameterSeparator = CheckIfChar(IsParameterSeparator);
      SkipIfChar(IsParameterSeparator);
    }
 
    ExpressionParserLocation invalidClosingParenthesisLocation;
    return ParametersNode{
        std::move(parameters),
        RaiseSyntaxError(_("The list of parameters is not terminated. Add a "
                           "closing parenthesis to end the parameters.")),
        invalidClosingParenthesisLocation};
  }
 
  std::unique_ptr<ExpressionParserError> ValidateOperator(
      gd::String::value_type operatorChar) {
    if (operatorChar == '+' || operatorChar == '-' || operatorChar == '/' ||
        operatorChar == '*') {
      return std::unique_ptr<ExpressionParserError>(nullptr);
    }
    return gd::make_unique<ExpressionParserError>(
        gd::ExpressionParserError::ErrorType::InvalidOperator,
        _("You've used an operator that is not supported. Operator should be "
          "either +, -, / or *."),
        GetCurrentPosition());
  }
 
  std::unique_ptr<ExpressionParserError> ValidateUnaryOperator(
      gd::String::value_type operatorChar,
      size_t position) {
    if (operatorChar == '+' || operatorChar == '-') {
      return std::unique_ptr<ExpressionParserError>(nullptr);
    }
 
    return gd::make_unique<ExpressionParserError>(
        gd::ExpressionParserError::ErrorType::InvalidOperator,
        _("You've used an \"unary\" operator that is not supported. Operator "
          "should be "
          "either + or -."),
        position);
  }
 
  ExpressionParserLocation SkipChar() {
    size_t startPosition = currentPosition;
    return ExpressionParserLocation(startPosition, ++currentPosition);
  }
 
  void SkipAllWhitespaces() {
    while (currentPosition < expression.size() &&
           IsWhitespace(expression[currentPosition])) {
      currentPosition++;
    }
  }
 
  void SkipIfChar(
      const std::function<bool(gd::String::value_type)> &predicate) {
    if (CheckIfChar(predicate)) {
      currentPosition++;
    }
  }
 
  ExpressionParserLocation SkipNamespaceSeparator() {
    size_t startPosition = currentPosition;
    // Namespace separator is a special kind of delimiter as it is 2 characters
    // long
    if (IsNamespaceSeparator()) {
      currentPosition += NAMESPACE_SEPARATOR.size();
    }
 
    return ExpressionParserLocation(startPosition, currentPosition);
  }
 
  bool CheckIfChar(
      const std::function<bool(gd::String::value_type)> &predicate) {
    if (currentPosition >= expression.size()) return false;
    gd::String::value_type character = expression[currentPosition];
 
    return predicate(character);
  }
 
  bool IsNamespaceSeparator() {
    // Namespace separator is a special kind of delimiter as it is 2 characters
    // long
    return (currentPosition + NAMESPACE_SEPARATOR.size() <= expression.size() &&
            expression.substr(currentPosition, NAMESPACE_SEPARATOR.size()) ==
                NAMESPACE_SEPARATOR);
  }
 
  bool IsEndReached() { return currentPosition >= expression.size(); }
 
  // A temporary node used when reading an identifier
  struct IdentifierAndLocation {
    gd::String name;
    ExpressionParserLocation location;
  };
 
  IdentifierAndLocation ReadIdentifierName(bool allowDeprecatedSpacesInName = true) {
    gd::String name;
    size_t startPosition = currentPosition;
    while (currentPosition < expression.size() &&
           (CheckIfChar(IsAllowedInIdentifier)
            // Allow whitespace in identifier name for compatibility
            || (allowDeprecatedSpacesInName && expression[currentPosition] == ' '))) {
      name += expression[currentPosition];
      currentPosition++;
    }
 
    // Trim whitespace at the end (we allow them for compatibility inside
    // the name, but after the last character that is not whitespace, they
    // should be ignore again).
    if (!name.empty() && IsWhitespace(name[name.size() - 1])) {
      size_t lastCharacterPos = name.size() - 1;
      while (lastCharacterPos < name.size() &&
             IsWhitespace(name[lastCharacterPos])) {
        lastCharacterPos--;
      }
      if ((lastCharacterPos + 1) < name.size()) {
        name.erase(lastCharacterPos + 1);
      }
    }
 
    IdentifierAndLocation identifierAndLocation{
        name,
        // The location is ignoring the trailing whitespace (only whitespace
        // inside the identifier are allowed for compatibility).
        ExpressionParserLocation(startPosition, startPosition + name.size())};
    return identifierAndLocation;
  }
 
  std::unique_ptr<TextNode> ReadText();
 
  std::unique_ptr<NumberNode> ReadNumber();
 
  std::unique_ptr<EmptyNode> ReadUntilWhitespace() {
    size_t startPosition = GetCurrentPosition();
    gd::String text;
    while (currentPosition < expression.size() &&
           !IsWhitespace(expression[currentPosition])) {
      text += expression[currentPosition];
      currentPosition++;
    }
 
    auto node = gd::make_unique<EmptyNode>(text);
    node->location =
        ExpressionParserLocation(startPosition, GetCurrentPosition());
    return node;
  }
 
  std::unique_ptr<EmptyNode> ReadUntilEnd() {
    size_t startPosition = GetCurrentPosition();
    gd::String text;
    while (currentPosition < expression.size()) {
      text += expression[currentPosition];
      currentPosition++;
    }
 
    auto node = gd::make_unique<EmptyNode>(text);
    node->location =
        ExpressionParserLocation(startPosition, GetCurrentPosition());
    return node;
  }
 
  size_t GetCurrentPosition() { return currentPosition; }
 
  gd::String::value_type GetCurrentChar() {
    if (currentPosition < expression.size()) {
      return expression[currentPosition];
    }
 
    return '\n';  // Should not arise, unless GetCurrentChar was called when
                  // IsEndReached() is true (which is a logical error).
  }
 
  std::unique_ptr<ExpressionParserError> RaiseSyntaxError(
      const gd::String &message) {
    return std::move(gd::make_unique<ExpressionParserError>(
        gd::ExpressionParserError::ErrorType::SyntaxError, message,
        GetCurrentPosition()));
  }
 
  std::unique_ptr<ExpressionParserError> RaiseTypeError(
      const gd::String &message, size_t beginningPosition) {
    return std::move(gd::make_unique<ExpressionParserError>(
        gd::ExpressionParserError::ErrorType::MismatchedType, message,
        beginningPosition, GetCurrentPosition()));
  }
 
  gd::String expression;
  std::size_t currentPosition;
 
  static gd::String NAMESPACE_SEPARATOR;
};
 
}  // namespace gd
 
#endif  // GDCORE_EXPRESSIONPARSER2_H