Add expression evaluation

cclox_src/error_handler.cc

@@ -14,6 +14,11 @@ void ErrorHandler::error(Token token, const std::string &message) {
   }
 }
 
+void ErrorHandler::runtime_error(const RuntimeException &exception) {
+  std::cout << "RuntimeException [" << exception.token.line << "]: " << exception.what() << '\n';
+  had_runtime_error = true;
+}
+
 void ErrorHandler::report(int line, const std::string &where, const std::string &message) {
   std::cout << "[line " << line << "] Error" << where << ": " << message << '\n';
   had_error = true;

cclox_src/error_handler.hh

@@ -2,15 +2,29 @@
 #define ERROR_HANDLER_HH
 
 #include "tokenizer.hh"
+#include <exception>
 #include <string>
 
+struct RuntimeException : public std::exception {
+  RuntimeException(Token token, const std::string& message) : token{token}, message{message} {}
+  const char* what() const noexcept override {
+    return message.c_str();
+  }
+
+  Token token;
+private:
+  std::string message;
+};
+
 struct ErrorHandler {
   ErrorHandler() : had_error{false} {};
   void error(int line, const std::string &message);
   void error(Token token, const std::string &message);
+  void runtime_error(const RuntimeException &exception);
   void report(int line, const std::string &where, const std::string &message);
 
   bool had_error;
+  bool had_runtime_error;
 };
 
 #endif

cclox_src/interpreter.cc

@@ -35,6 +35,9 @@ void run_file(const char *path) {
     if (error_handler.had_error) {
       exit(EX_DATAERR);
     }
+    if (error_handler.had_runtime_error) {
+      exit(EX_SOFTWARE);
+    }
   }
 }
 
@@ -45,6 +48,7 @@ void run_prompt() {
     run(line);
     std::cout << PROMPT;
     error_handler.had_error = false;
+    error_handler.had_runtime_error = false;
   }
 }
 
@@ -55,8 +59,13 @@ void run(const std::string &code) {
   Parser parser{tokens};
   std::optional<Expr> expression = parser.parse();
 
+  static AstInterpreter interpreter{};
+
+  if (error_handler.had_error) {
+    return;
+  }
+
   if (expression) {
-    AstPrinter printer{};
-    std::cout << printer.print(*expression) << '\n';
+    interpreter.interpret(*expression);
   }
 }

cclox_src/parser.cc

@@ -4,5 +4,6 @@
 #include "parser/expr.cc"
 #include "parser/printer.cc"
 #include "parser/parser.cc"
+#include "parser/interpreter.cc"
 
 #endif

cclox_src/parser.hh

@@ -4,5 +4,6 @@
 #include "parser/expr.hh"
 #include "parser/printer.hh"
 #include "parser/parser.hh"
+#include "parser/interpreter.hh"
 
 #endif

cclox_src/parser/interpreter.cc

@@ -0,0 +1,168 @@
+#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;
+  }
+}

cclox_src/parser/interpreter.hh

@@ -0,0 +1,21 @@
+#ifndef AST_INTERPRETER_HH
+#define AST_INTERPRETER_HH
+
+#include "expr.hh"
+#include "../tokenizer.hh"
+#include <string>
+
+struct AstInterpreter {
+  void interpret(const Expr &expression);
+
+private:
+  Object evaluate(const Expr &expr);
+  Object evaluate_binary_expression(const Expr &expr);
+  Object evaluate_grouping_expression(const Expr &expr);
+  Object evaluate_literal_expression(const Expr &expr);
+  Object evaluate_unary_expression(const Expr &expr);
+  bool is_truthy(const Object &object);
+  bool is_equal(const Object &left, const Object &right);
+};
+
+#endif

cclox_src/scanner/object.cc

@@ -21,6 +21,35 @@ std::string Object::to_string() {
   }
 }
 
+bool Object::operator==(const Object &other) {
+  if (type != other.type) {
+    return false;
+  }
+
+  switch (type) {
+    case ObjectType::NIL: return true;
+    case ObjectType::BOOL: {
+      bool left  = std::get<bool>(value);
+      bool right = std::get<bool>(other.value);
+
+      return left == right;
+    }
+    case ObjectType::IDENTIFIER:
+    case ObjectType::STRING_LIT: {
+      std::string left  = std::get<std::string>(value);
+      std::string right = std::get<std::string>(other.value);
+
+      return left == right;
+    }
+    case ObjectType::NUMBER: {
+      double left  = std::get<double>(value);
+      double right = std::get<double>(other.value);
+
+      return left == right;
+    }
+  }
+}
+
 std::ostream &operator<<(std::ostream &os, const ObjectType &type) {
   switch (type) {
     case ObjectType::NIL:
@@ -64,3 +93,7 @@ std::ostream &operator<<(std::ostream &os, const Object &obj) {
 
   return os;
 }
+
+bool Object::operator!=(const Object &other) {
+  return !operator==(other);
+}

cclox_src/scanner/object.hh

@@ -30,6 +30,8 @@ struct Object {
       },
       value{std::move(value)} {};
   std::string to_string();
+  bool operator==(const Object &other);
+  bool operator!=(const Object &other);
 
   ObjectType type;
   std::variant<std::monostate, std::string, double, bool> value;