crafting-interpreters/cclox_src/parser/interpreter.cc

#include "interpreter.hh"
#include "expr.hh"
#include "../error_handler.hh"
#include "../tokenizer.hh"
#include <memory>
#include <string>
#include <cassert>
#include <iostream>

extern ErrorHandler error_handler;

void AstInterpreter::interpret(const Expr &expression) {
  try {
    Object value = evaluate(expression);
    std::cout << value.to_string() << '\n';
  } catch (RuntimeException e) {
    error_handler.runtime_error(e);
  }
}

Object AstInterpreter::evaluate(const Expr &expr) {
  switch (expr.type) {
    case ExprType::BINARY:
      return evaluate_binary_expression(expr);
    case ExprType::GROUPING:
      return evaluate_grouping_expression(expr);
    case ExprType::LITERAL:
      return evaluate_literal_expression(expr);
    case ExprType::UNARY:
      return evaluate_unary_expression(expr);
  }
}

Object AstInterpreter::evaluate_binary_expression(const Expr &expr) {
  std::shared_ptr<_Binary> ptr = std::get<std::shared_ptr<_Binary>>(expr.value);
  assert(ptr != nullptr);

  Object left  = evaluate(ptr->left);
  Object right = evaluate(ptr->right);

  if (left.type == ObjectType::NUMBER && right.type == ObjectType::NUMBER) {
    double left_val = std::get<double>(left.value);
    double right_val = std::get<double>(right.value);

    switch (ptr->op.type) {
      case TokenType::PLUS:  return left_val + right_val;
      case TokenType::MINUS: return left_val - right_val;
      case TokenType::STAR:  return left_val * right_val;
      case TokenType::SLASH: {
        if (right_val == 0) {
          throw RuntimeException{ptr->op, "Division by zero."};
        }
        return left_val / right_val;
      }

      case TokenType::GREATER:       return left_val > right_val;
      case TokenType::GREATER_EQUAL: return left_val >= right_val;
      case TokenType::LESS:          return left_val < right_val;
      case TokenType::LESS_EQUAL:    return left_val <= right_val;

      case TokenType::BANG_EQUAL:  return left_val != right_val;
      case TokenType::EQUAL_EQUAL: return left_val == right_val;

      default: throw RuntimeException{ptr->op, "Operator " + ptr->op.lexeme + " is not supported for numbers."};
    }
  }

  if (left.type == ObjectType::STRING_LIT) {
    right = Object{StringObjectType::LITERAL, right.to_string()};
  }

  if (right.type == ObjectType::STRING_LIT) {
    left = Object{StringObjectType::LITERAL, left.to_string()};
  }

  if (left.type == ObjectType::STRING_LIT && right.type == ObjectType::STRING_LIT) {
    std::string left_val = std::get<std::string>(left.value);
    std::string right_val = std::get<std::string>(right.value);

    switch (ptr->op.type) {
      case TokenType::PLUS: return Object{StringObjectType::LITERAL, left_val + right_val};

      case TokenType::BANG_EQUAL:  return left_val != right_val;
      case TokenType::EQUAL_EQUAL: return left_val == right_val;

      default: throw RuntimeException{ptr->op, "Operator " + ptr->op.lexeme + " is not supported for strings."};
    }
  }

  if (left.type == ObjectType::BOOL && right.type == ObjectType::BOOL) {
    bool left_val = std::get<bool>(left.value);
    bool right_val = std::get<bool>(right.value);

    switch (ptr->op.type) {
      case TokenType::BANG_EQUAL:  return left_val != right_val;
      case TokenType::EQUAL_EQUAL: return left_val == right_val;

      default: throw RuntimeException{ptr->op, "Operator " + ptr->op.lexeme + " is not supported for booleans."};
    }
  }

  if (left.type == ObjectType::NIL && right.type == ObjectType::NIL) {
    switch (ptr->op.type) {
      case TokenType::BANG_EQUAL:  return false;
      case TokenType::EQUAL_EQUAL: return true;

      default: throw RuntimeException{ptr->op, "Operator " + ptr->op.lexeme + " is not supported for null."};
    }
  }

  if (left.type == ObjectType::NIL) {
    switch (ptr->op.type) {
      case TokenType::BANG_EQUAL:  return true;
      case TokenType::EQUAL_EQUAL: return false;

      default: break;
    }
  }

  throw RuntimeException{ptr->op, "Operator " + ptr->op.lexeme + " is not supported for operands " + left.to_string() + " and " + right.to_string() + "."};
}

Object AstInterpreter::evaluate_grouping_expression(const Expr &expr) {
  std::shared_ptr<_Grouping> ptr = std::get<std::shared_ptr<_Grouping>>(expr.value);
  assert(ptr != nullptr);
  return evaluate(ptr->expr);
}

Object AstInterpreter::evaluate_literal_expression(const Expr &expr) {
  std::shared_ptr<_Literal> ptr = std::get<std::shared_ptr<_Literal>>(expr.value);
  assert(ptr != nullptr);
  return ptr->value;
}

Object AstInterpreter::evaluate_unary_expression(const Expr &expr) {
  std::shared_ptr<_Unary> ptr = std::get<std::shared_ptr<_Unary>>(expr.value);
  assert(ptr != nullptr);

  Object right = evaluate(ptr->right);

  switch (ptr->op.type) {
    case TokenType::MINUS: {
      switch (right.type) {
        case ObjectType::NUMBER: {
          double value = std::get<double>(right.value);
          return -value;
        }
        default: throw RuntimeException{ptr->op, "Operand to unary operator - must be a number."};
      }
    }
    case TokenType::BANG:
      return !is_truthy(right);
    default: break;
  }

  return Object{};
}

bool AstInterpreter::is_truthy(const Object &object) {
  switch (object.type) {
    case ObjectType::NIL: return false;
    case ObjectType::BOOL: {
      bool value = std::get<bool>(object.value);
      return value;
    }
    default: return true;
  }
}