public object Visit(Expr.Super expr)
{
if (currentClass == ClassType.None)
{
Lox.Error(expr.keyword, "Cannot use 'super' outside of a class.");
}
else if (currentClass != ClassType.Subclass)
{
Lox.Error(expr.keyword, "Cannot use 'super' in a class with no superclass.");
}
ResolveLocal(expr, expr.keyword);
return(null);
}
private Expr Primary()
{
Expr expr = null;
if (Match(TokenType.False))
{
expr = new Expr.Literal(false);
}
else if (Match(TokenType.True))
{
expr = new Expr.Literal(true);
}
else if (Match(TokenType.Nil))
{
expr = new Expr.Literal(null);
}
else if (Match(TokenType.Number, TokenType.String))
{
expr = new Expr.Literal(Previous().literal);
}
else if (Match(TokenType.Super))
{
Token keyword = Previous();
Consume(TokenType.Dot, "Expect '.' after 'super'.");
Token method = Consume(TokenType.Identifier, "Expect superclass method name.");
expr = new Expr.Super(keyword, method);
}
else if (Match(TokenType.This))
{
expr = new Expr.This(Previous());
}
else if (Match(TokenType.Identifier))
{
expr = new Expr.Variable(Previous());
}
else if (Match(TokenType.LeftParen))
{
expr = Expression();
Consume(TokenType.RightParen, "Expect ')' after expression.");
expr = new Expr.Grouping(expr);
}
else
{
throw Error(Peek(), "Expect expression.");
}
return(expr);
}
public object Visit(Expr.Super expr)
{
int distance = locals[expr];
LoxClass superclass = (LoxClass)environment.GetAt(distance, "super");
// "this" is always one level nearer than "super"'s environment;
LoxInstance obj = (LoxInstance)environment.GetAt(distance - 1, "this");
LoxFunction method = superclass.FindMethod(obj, expr.method.lexeme);
if (method == null)
{
throw new RuntimeError(expr.method, "Undefined property '" + expr.method.lexeme + ".");
}
return(method);
}
