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Interpreter.h
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Interpreter.h
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#pragma once
#include <any>
#include <iostream>
#include <memory>
#include <stdexcept>
#include <string>
#include <vector>
#include <utility> // std::move
#include "Environment.h"
#include "Error.h"
#include "Expr.h"
#include "RuntimeError.h"
#include "Stmt.h"
class Interpreter: public ExprVisitor,
public StmtVisitor {
std::shared_ptr<Environment> environment{new Environment};
public:
void interpret(const std::vector<
std::shared_ptr<Stmt>>& statements) {
try {
for (const std::shared_ptr<Stmt>& statement : statements) {
execute(statement);
}
} catch (RuntimeError error) {
runtimeError(error);
}
}
private:
std::any evaluate(std::shared_ptr<Expr> expr) {
return expr->accept(*this);
}
void execute(std::shared_ptr<Stmt> stmt) {
stmt->accept(*this);
}
void executeBlock(
const std::vector<std::shared_ptr<Stmt>>& statements,
std::shared_ptr<Environment> environment) {
std::shared_ptr<Environment> previous = this->environment;
try {
this->environment = environment;
for (const std::shared_ptr<Stmt>& statement : statements) {
execute(statement);
}
} catch (...) {
this->environment = previous;
throw;
}
this->environment = previous;
}
public:
std::any visitBlockStmt(std::shared_ptr<Block> stmt) override {
executeBlock(stmt->statements,
std::make_shared<Environment>(environment));
return {};
}
std::any visitExpressionStmt(
std::shared_ptr<Expression> stmt) override {
evaluate(stmt->expression);
return {};
}
std::any visitPrintStmt(std::shared_ptr<Print> stmt) override {
std::any value = evaluate(stmt->expression);
std::cout << stringify(value) << "\n";
return {};
}
std::any visitVarStmt(std::shared_ptr<Var> stmt) override {
std::any value = nullptr;
if (stmt->initializer != nullptr) {
value = evaluate(stmt->initializer);
}
environment->define(stmt->name.lexeme, std::move(value));
return {};
}
std::any visitAssignExpr(std::shared_ptr<Assign> expr) override {
std::any value = evaluate(expr->value);
environment->assign(expr->name, value);
return value;
}
std::any visitBinaryExpr(std::shared_ptr<Binary> expr) override {
std::any left = evaluate(expr->left);
std::any right = evaluate(expr->right);
switch (expr->op.type) {
case BANG_EQUAL: return !isEqual(left, right);
case EQUAL_EQUAL: return isEqual(left, right);
case GREATER:
checkNumberOperands(expr->op, left, right);
return std::any_cast<double>(left) >
std::any_cast<double>(right);
case GREATER_EQUAL:
checkNumberOperands(expr->op, left, right);
return std::any_cast<double>(left) >=
std::any_cast<double>(right);
case LESS:
checkNumberOperands(expr->op, left, right);
return std::any_cast<double>(left) <
std::any_cast<double>(right);
case LESS_EQUAL:
checkNumberOperands(expr->op, left, right);
return std::any_cast<double>(left) <=
std::any_cast<double>(right);
case MINUS:
checkNumberOperands(expr->op, left, right);
return std::any_cast<double>(left) -
std::any_cast<double>(right);
case PLUS:
if (left.type() == typeid(double) &&
right.type() == typeid(double)) {
return std::any_cast<double>(left) +
std::any_cast<double>(right);
}
if (left.type() == typeid(std::string) &&
right.type() == typeid(std::string)) {
return std::any_cast<std::string>(left) +
std::any_cast<std::string>(right);
}
// break;
throw RuntimeError{expr->op,
"Operands must be two numbers or two strings."};
case SLASH:
checkNumberOperands(expr->op, left, right);
return std::any_cast<double>(left) /
std::any_cast<double>(right);
case STAR:
checkNumberOperands(expr->op, left, right);
return std::any_cast<double>(left) *
std::any_cast<double>(right);
}
// Unreachable.
return {};
}
std::any visitGroupingExpr(
std::shared_ptr<Grouping> expr) override {
return evaluate(expr->expression);
}
std::any visitLiteralExpr(std::shared_ptr<Literal> expr) override {
return expr->value;
}
std::any visitUnaryExpr(std::shared_ptr<Unary> expr) override {
std::any right = evaluate(expr->right);
switch (expr->op.type) {
case BANG:
return !isTruthy(right);
case MINUS:
checkNumberOperand(expr->op, right);
return -std::any_cast<double>(right);
}
// Unreachable.
return {};
}
std::any visitVariableExpr(
std::shared_ptr<Variable> expr) override {
return environment->get(expr->name);
}
private:
void checkNumberOperand(const Token& op,
const std::any& operand) {
if (operand.type() == typeid(double)) return;
throw RuntimeError{op, "Operand must be a number."};
}
void checkNumberOperands(const Token& op,
const std::any& left,
const std::any& right) {
if (left.type() == typeid(double) &&
right.type() == typeid(double)) {
return;
}
throw RuntimeError{op, "Operands must be numbers."};
}
bool isTruthy(const std::any& object) {
if (object.type() == typeid(nullptr)) return false;
if (object.type() == typeid(bool)) {
return std::any_cast<bool>(object);
}
return true;
}
bool isEqual(const std::any& a, const std::any& b) {
if (a.type() == typeid(nullptr) && b.type() == typeid(nullptr)) {
return true;
}
if (a.type() == typeid(nullptr)) return false;
if (a.type() == typeid(std::string) &&
b.type() == typeid(std::string)) {
return std::any_cast<std::string>(a) ==
std::any_cast<std::string>(b);
}
if (a.type() == typeid(double) && b.type() == typeid(double)) {
return std::any_cast<double>(a) == std::any_cast<double>(b);
}
if (a.type() == typeid(bool) && b.type() == typeid(bool)) {
return std::any_cast<bool>(a) == std::any_cast<bool>(b);
}
return false;
}
std::string stringify(const std::any& object) {
if (object.type() == typeid(nullptr)) return "nil";
if (object.type() == typeid(double)) {
std::string text = std::to_string(
std::any_cast<double>(object));
if (text[text.length() - 2] == '.' &&
text[text.length() - 1] == '0') {
text = text.substr(0, text.length() - 2);
}
return text;
}
if (object.type() == typeid(std::string)) {
return std::any_cast<std::string>(object);
}
if (object.type() == typeid(bool)) {
return std::any_cast<bool>(object) ? "true" : "false";
}
return "Error in stringify: object type not recognized.";
}
};